Effect of Ultrasound on Hydrogen Bond
Breaking Appeared in Aqueous Polymers
(水溶性高分子の水素結合切断を誘発する超音波効果に関する研究 )
Venegas-Sánchez Josué Addiel
(ベネガスサンチェスホスエアヂィエル)
Energy and Environmental Science
Nagaoka University of Technology
June 2013
II
Acknowledgments
I wish to express my deepest gratitude to Prof. Dr, Takaomi Kobashi
in Department of
Material Science and Technology, Nagaoka University of Technology, Nagaoka, Japan,
for his invaluable guidance, encouragement and support through my study during the
period from September 2009 to June 2013.
Furthermore, I am grateful to Prof. Yoshio Nosaka, Prof. Minoru Umeda and Prof.
Imakubo Tatsurou in Nagaoka University of Technology and Prof. Kazunori Murayama
in Nagaoka National College of Technology for their for their comments and
suggestions to evaluate my thesis.
I would like to thank Assist. Prof. Motohiro Tagaya for his kindly support, comments
and suggestions during doctoral program.
My most sincere gratitude is to Japanese Government, Ministry of education, Science,
Sport and Culture for financial support for my doctoral program.
Last but not least, my special thanks and gratitude to my parents Jose Venegas and
Blanca Sanchez, Anchalee Saengsai, aunts, uncles and all the international friends I did.
Their support and encouragement were the inspiration and motivation for my, through
this road of life.
Josué Addiel Venegas Sanchez
June 2013
III
IV
Table of Contents
1 Chapter 1 Introduction ............................................................................................... 1
1.1 Introduction on ultrasound ...................................................................................... 1
1.2 General scope on sonoprocess ................................................................................ 1
1.2.1 Sonochemistry and sonoprocessing .................................................................. 2
1.2.2 Basic background of US technology using for sonoprocess ............................ 7
1.3 Research in sonoprocess ....................................................................................... 11
1.3.1 Research examples in sonoproces .................................................................. 11
1.3.2 Sonoprocessing applied to polymeric materials. ............................................ 13
1.3.3 Sonoprocessing research in Nagaoka ............................................................. 14
1.4 Scope of present investigation .............................................................................. 18
2 Chapter 2 Ultrasound Effect Used as External Stimulus for Viscosity Change of
Aqueous Carrageenans ................................................................................................ 25
2.1 Introduction ........................................................................................................... 26
2.2 Experimental ......................................................................................................... 29
2.2.1 Materials ......................................................................................................... 29
2.2.2 Measurements of shear viscosity of aqueous polysaccharides. ...................... 29
2.2.3 Determination of US effect on FT-IR spectra of the polysaccharide
solutions ................................................................................................................... 32
2.3 Results and discussion .......................................................................................... 34
2.3.1 Effect of ultrasound on shear viscosity of polysaccharides solutions ............ 34
V
2.3.2 Measurement of US effect on FT-IR spectra of polysaccharide solutions ..... 37
2.4 Conclusion ............................................................................................................ 51
3 Chapter 3 Ultrasound Stimulus Inducing Change in Hydrogen Bonded
Crosslinking of Aqueous Polyvinyl Alcohols ............................................................. 55
3.1 Introduction ........................................................................................................... 55
3.2 Experimental ......................................................................................................... 58
3.2.1 Materials and sample solution preparation ..................................................... 58
3.2.2 Ultrasound equipment and its evaluation. ...................................................... 58
3.2.3 Shear viscosity measurement of PVA aqueous solutions............................... 62
3.2.4 Measurements of US effects on FT-IR spectra of the aqueous PVA
solutions ................................................................................................................... 63
3.3 Results and discussion .......................................................................................... 63
3.3.1 Change in the shear viscosity of aqueous PVA during US exposure ............. 63
3.3.2 Effect of US absorption on the PVA aqueous medium .................................. 65
3.3.3 Change in FT-IR spectra observed at different times ..................................... 74
3.4 Conclusion ............................................................................................................ 91
4 Chapter 4 Effect of Ultrasound on Changing Aqueous Viscosity of Several Water
Soluble Polymers .......................................................................................................... 97
4.1 Introduction ........................................................................................................... 98
4.2 Experimental ....................................................................................................... 100
4.2.1 Materials and sample solution preparation ................................................... 100
4.2.2 Shear viscosity measurements of the water-soluble polymers ..................... 100
VI
4.2.3 Measurements of the US effect on the FT-IR spectra of the aqueous
solutions. ................................................................................................................ 102
4.3 Results and discussion ........................................................................................ 103
4.3.1 Effect of ultrasound on shear viscosity of water soluble polymers. ............. 103
4.3.2 Effect of US absorption on the aqueous polymer medium. .......................... 105
4.3.3 Effect of ultrasound on change in FT-IR spectra of water soluble
polymers. ............................................................................................................... 109
4.4 Conclusion .......................................................................................................... 132
5 Chapter 5 Sono-respond on Thermosensitive Polymer Microgels Based on
Cross-linked Poly(N-isopropylacrylamide-co-acrylic acid) .................................... 139
5.1 Introduction ......................................................................................................... 140
5.2 Experimental ....................................................................................................... 142
5.3 Results and discussion ........................................................................................ 148
5.3.1 US influenced thermo-sensitivity of microgels ............................................ 148
5.3.2 FT-IR spectroscopic study for US effect on thermo-sensitive microgels .... 153
5.4 Conclusion .......................................................................................................... 159
6 Chapter 6 Summary ................................................................................................ 163
1 List of Achievements ............................................................................................... 167
2 International and National Conference Proceeding ............................................. 168
VII
VIII
1 Chapter 1 Introduction
1.1 Introduction on ultrasound
Ultrasound (US) is a technology that has been described for first time in 19th century,
when the first whistle for the production of sound has been developed by Francis Galton
for investigation to human threshold of the human earing. Years later, Paul Langevin
invented the first echo-sounder. Eventually his invention became the underwater
SONAR for submarine detection during 2nd World War. Then, this innovation was
used to apply for medical spot in clinical treatment in order to take body inside imagine
by US and enable the detection of different tissue structures in patient body for medical
diagnosis. In this case, high frequency US in the range of 2 to 10 MHz was utilized
primarily as its application. Using shorter US frequencies could be possible to detect
much smaller areas of phases changes. The first industrial application of US was an
ultrasonic flaw detection system, later know as an ―inspecto-scope‖ in construction
industry. It was known that this system was used for locating flaws in materials and for
measuring the thickness of materials which only one face was available [1, 2].
1.2 General scope on sonoprocess
As introduce above, the US technology has been developing in several fields. It can be
summarized that the US frequency range is able to be divided into two parts (Figure
1
Chapter 1 Introduction
1-1). Power US which is capable of influencing chemistry and processing and is mainly
in the frequency range between 20 kHz and 100 kHz. Diagnostic US which does not
have enough power to produce cavitation, is at very high frequencies (above 5 MHz)
and is used in for example in fetal scanning [3].
Figure 1-1 Frequency ranges of sound
1.2.1 Sonochemistry and sonoprocessing
Sonochemistry is the application of US energy to chemical reactions. US is transmitted
through a medium using pressure waves by including vibrational motion of the
molecules which alternately compress and stretch the molecular structure of the medium
due to a time-varying pressure (Figure 1-2). The distances among the molecules vary as
the molecules oscillate around their mean position. If the intensity of US is increased in
2
Chapter 1 Introduction
Figure 1-2 Sound motion in a medium
a liquid, a point is reached at which the intramolecular forces are no able to hold the
molecular structure intact. Consequently, it breaks down and cavitation bubbles are
created. This process is called cavitation and the point at which it starts is known as the
cavitation threshold [4]. Cavitation phenomenon was first identified and reported in
1895 by Sir John Thorneycroft and Sidney Barnaby. When they observed in the
propeller of their submarine, became to be pitted and eroded over a relatively short
operation period. Then, the result introduced to cavitation bubbles. Lord Rayleigh
produced a seminar work in the field of cavitation, when it was confirmed that the
cavitation effects were due to the enormous turbulence, heat and pressure in US medium.
Here, the temperature was around 5000 K and pressures of the order of 2000 atm, when
cavitation imploded on or near to the propeller surface of the bubbles [1-3]. The
chemical effects of US are diverse and included as dramatic improvements at
3
Chapter 1 Introduction
sonochemistry for both stoichiometric and catalytic reactions. The current major areas
of sonochemistry in the research are included in Table 1-1.
Ultrasonic processing is based on the adequate exploitation of the nonlinear effects
associated to the high-intensity ultrasonic waves. The most relevant nonlinear effects
related to high-amplitude waves are followed in: wave distortion, radiation pressure,
acoustic streaming, cavitation in liquids and the formation and motion of dislocation
loops in solids. As a consequence of these effects, a series of mechanisms may be
activated by the ultrasonic energy such as heat, agitation, diffusion, interface
instabilities, friction, mechanical rupture, chemical effects, etc. Such mechanisms can
be employed to produce or to enhance a wide range of processes that depend well on the
irradiated medium [5]. On the other hand, industrial and commercial applications of US
have been reviewed [6, 7]. Applications employing higher powers generally rely on
compound vibration-induced phenomena occurring in the object or in material irradiated.
These phenomena include as following phenomenon, cavitation and microstreaming in
liquids, heating and fatiguing in solids, and induction of surface in stability at
liquid-liquid and liquid-gas inter faces. Some of the more common applications of high
power US are shown in Tabla 1-2. This also provides a description of the application
4
Chapter 1 Introduction
Table 1-1 Major research fields in Sonochemistry
Application of
Sonochemistry
Description
Synthesis
(Green
Chemistry)
The use of less hazardous chemicals and environmentally friendly
solvents.
Developing reaction conditions to increase the selectivity for the
product.
Minimizing the energy consumption for chemical transformations.
Continuous cleaning and activation of the electrode surfaces
Degassing which limits gas bubble accumulation on the electrode
Electrochemistry surface
Agitation (via cavitation) which disturbs and reduces the thickness of
the diffusion layer
In water treatment, the destruction/transformation of organic
compounds is the prime objective of fundamental and applied
investigations.
Processes such as ozonation with US or an integrated
Environmental
protection
ultrasonic/biological treatment can significantly improve process
efficiency and economy.
The violent collapse of cavitation bubbles in water produces shear
forces that can disrupt cell membranes and kill bacteria.
The hydroxyl radical produced during cavitation can also assist
disinfection.
Preparation and modification of nanoparticles:
(a) The ability to produce the nanomaterials in the amorphous state
which is due to the very high cooling rates (>1011 K/s) obtained in
the collapsing cavitation bubble during sonochemistry.
(b) Sonication generally results in shorter reaction times.
(c) Insertion and coating processes.
Material science
Surface modification of materials used in electronics manufacturing:
Traditional manufacturing techniques for surface modification often
use hazardous chemicals (hot alkaline permanganate for polymer
composites and hydrofluoric acid for ceramics). Recently, it have been
explored the use of power US and water without added chemicals to
produce similar surface modification.
5
Chapter 1 Introduction
Table 1-2 Industrial applications of high power US.
Application
Description
Frequency [kHz]
Intensity Range
Usually below 10
Cavitated cleaning solution
Cleaning and degreasing
18 – 100
W/cm2 but up to
scrubs parts
100W power
Displacement of oxide film
Soldering and braising
to accomplish bonding
Around 30
2 - 200 W/cm2
without flux
Usually 20 – 30
Welding soft and rigid
Plastic welding
20-60
W/cm2 but power
plastic
below 1000W output
Welding similar /
Metal welding
10 – 60
Up to 10,000 W/cm2
Around 20
About 500 W/cm2
20 – 30 000
Up to 800W
Around 27
30 W
Around 20
About 150W
dissimilar metals
Extracting perfume, juices,
Extraction
chemicals from f lowers,
plants
Fuel atomization to
improve combustion
Atomization
efficiency and reduce
pollution
Emulsification ,dispersion,
Mixing and homogenizing
and homogenization
of liquids, slurries, creams
Separation of foam and
Defoaming and degassing
gas from liquid
Increases plating rates and
Electroplating
produces denser, more
uniform deposit
Drying heat sensitive
Drying
powders, food - stuff,
pharmaceuticals
Cutting small holes in
Cutting
ceramics, glass and
semi-conductors
6
Chapter 1 Introduction
and US frequency and power or intensity range used, where these parameters are known.
One notes that the most practical frequency range for these applications is 20-100 kHz.
Most of industrial uses of US is produced using electrostrictive or magnetostrictive
transducers, where the elements change their physical dimensions in response to an
applied electric or magnetic field.
1.2.2 Basic background of US technology using for sonoprocess
Sonochemistry and sonoprocessing are based on chemical and physical phenomena in
ultrasonic field applied with cavitation behavior and other sonic effects. Here, the
cavitation becomes very important to consider sonochemistry. There are two different
types of cavitation occurred in the US field. One is inertial cavitation and non-inertial
cavitation for the sonochemistry. Inertial cavitation is occurred, when a micro-bubble
rapidly expands and violently collapses in a liquid medium. Inertial cavitation generally
is observed at higher acoustic pressures. Non-inertial cavitation is taken place at lower
acoustic pressures. Contrary to inertial cavitation, collapse of the microbubbles shows
and happens without violent [8, 9]. It is known that shock waves are produced when a
bubble is exposed to high acoustic pressures in conjunction with higher amplitudes and
nonlinear oscillations in bubble volume. As the bubble contracts from its maximum to
minimum radius, the surrounding fluid may gain momentum. The rising pressure within
7
Chapter 1 Introduction
the bubble is unable to resist the fluid coming in the microbubbles. The radius of the
bubble decreases rapidly and collapses. This is called ―inertial collapse‖ because the
inertia from the fluid dominates this motion. During an inertial collapse, the speed of
the gas-liquid interface may become very high. In extreme cases, it may be supersonic
in the liquid. These supersonic motions produce shock waves within the bubble and
surrounding fluid. The shock in the surrounding fluid will propagate outward [10, 11].
Knorr et al. used US combined with direct steam injection for the inactivation of
different lactobacillus. Results showed that the total energy requirements for
inactivation of micro-organisms suggests that ultrasound assisted thermal processing of
liquid foods can be achieved at lower temperature and can result in further quality
advantages [12]. Patist et al. has been reported that using the effect of shock waves
results in the formation of very fine, highly stable emulsions. This has been well
commercialized in the petrochemical, polymer, chemical, textile, cosmetics and
pharmaceutical industries and is now being developed in-line for food products such as
fruit juices, mayonnaise and tomato ketchup [13]. In addition with the effect of shock
wave, there is free radicals occurred at high temperatures. So the surrounding water has
the ability to dissociate. High temperatures may occur, when a bubble undergoes inertial
collapse. There is a brief time when the bubble is at its minimum radius and at this time,
8
Chapter 1 Introduction
the pressure in the bubble may increase to hundreds or thousands of mega Pascal.
Consequently the temperature may reach thousands of Kelvin. The interior of a bubble
contains mostly water vapor and high temperatures may lead to the formation of free
radicals, such as H• and OH• by dissociation of water. Free radicals are chemically
reactive and are potentially very damaging to any tissue they come in contact with [14].
It was known as sonoreaction that Ashokkumar et al. studied fenol in a model of food
compound, since phenolic compounds are ingredients in many food materials. The
results showed that selective hydroxylation of certain food chemicals using the
cavitation generated hydroxyl radicals may enhance their functional properties. The
sonochemical hydroxylation of phenolic compounds seems to be a viable process for
enhancing their antioxidant properties, in the area food extraction/processing as
applications [15]. Riener et al. investigated US induced off-flavour in milk. The results
of the study showed that the rubbery aroma was less intense on reducing the sonication
power from 400 to 100 W, however could not be totally eliminated. Still work is
required to see if it is possible to remove adverse aspects of sonication of milk [16]. On
the other hand, microstreaming occurs when oscillating bubbles in a sound field
produce a vigorous circulatory motion (Figure 1-3). These oscillating bubbles can be
pushed by an acoustic force produced from the traveling wave. A non-circulatory
9
Chapter 1 Introduction
shearing flow may result in the surrounding fluid. The fluid velocity is greatest near the
bubble surface and decreases with increasing distance from the bubble. Because of this
velocity change with respect to distance from the bubble surface, a gradient exists in the
region of fluid around the bubble [17]. Mason et al. found that US could be applied for
biological decontamination of water. In their research, US was applied using two
flow-through systems a pull-push system and a sonoxide system, decontamination does
occur but not very rapidly. However, that apparatus of this type would normally be used
in a closed loop to bring down contamination to an acceptable low level over a period of
time [18]. As well, Suri et al. observed that due to microstreaming, the mixing speed
increases with the applied power, then, reaches a plateau value. Using two transducers
in the same direction can significantly reduce the mixing time. Considering the
simplicity of a mixer which does not contain moving parts. It is certain that the
Figure 1-3 Microstreaming pattern near a pulsating hemisphere bubble trapped
10
Chapter 1 Introduction
development and industrial application of such a device would offer several advantages
over presently used mixers [19].
1.3 Research in sonoprocess
Scheme 1-1 shows some of the major researches areas in sonochemistry and
sonoprocess.
1.3.1 Research examples in sonoproces
The application of US to chemical process can be seen as sonoprocesses. In this case,
acoustic field needs be controlled not only by both US frequency and intensity, but also
the shape and size of sonochemical reactor including US equipment. Li et al. and
Ruecroft et al. studied US application in the crystallization [20, 21]. Other application
of US relates in processing for food drying by Fuente-Blanco et al. Their work was
reported that using US at 20 kHz was applied in a prototype of ultrasonic drying system
having US power in the range of 0 - 100 W. As the frequency was kept with constants,
the intensity increased the sample weight to be decreased especially at 100 W. Other
parameters such as temperature, flow rate suction, also were kept constant in the
sonoprosses [22]. Riera-Franco et al. explored the application of US for separation of
fluid/solid particles. It was noted that when US enhanced the agglomeration of particle
removal from coal combustion fumes. The ultrasonic energy was demonstrated to be
11
Chapter 1 Introduction
Scheme 1-1 Sonochemistry and Sonoprocess researches fields
12
Chapter 1 Introduction
very useful in assisting the dewatering of high-concentrated suspensions of fine
particles such as slurries and sludges [23].
1.3.2 Sonoprocessing applied to polymeric materials.
It has been mentioned that different application of US is widely known and used to be
external stimuli for US in some soft maters. In recent years, such US has been
recognized to be a new kind of stimuli to control material nature for polymeric systems.
In these cases, low US frequency was applied to encapsulated drugs and the
hydrophilicity and high permeability of the materials improved the penetration of water
[24, 25]. Rapoport studied US responsive drug delivery systems with tumor targeting
property. Their results showed that US irradiation could enhance the intracellular drug
uptake of the tumor cells and trigger localized drug release from nanoparticles via
perturbing tumor cell membranes [26]. Naota et al. reported that US releases the
self-lock in different dipeptides to cleave the intramolecular -stacking interactions of
the complexes, inducing rapid and spontaneous aggregation. The increase in the
duration of sonication accelerate the gelation rates and formation of higher-order
nanostructures with heat-resistant properties [27].
13
Chapter 1 Introduction
1.3.3 Sonoprocessing research in Nagaoka
Previous works on sonoprocessing in our laboratory at Nagaoka are shown as following
examples. It was studied the effect of US in TiO2 nano-sized powders preparation for
photodegradation of rhodamine 640 dye (Rh-640 Scheme 1-2 ). The results showed that
powders prepared US effect in the presence of a reflection plate (RP) has smaller
particle size that in those synthesized without RP. The photodegradation of Rh-640 by
the powder under synthesized with RP and low frequency were strongly activated to
decompose the Rh-640 dye in addition to high adsorptivity of the dye [28].
Scheme 1-2 Chemical structure of Rhodamine 640 dye
Copolymer microgels of N-isopropylacrylamide (NIPAM) and acrylic acid (AA) using
methylenebisacrylamide as a croslinker (Scheme 1-3) showed US responded behavior
in spherically polymer microgels. This was because that the hydrodynamic diameter of
14
Chapter 1 Introduction
microgel was shifted toward larger regions and the volume phase transition was also
elevated toward higher temperature side by US exposure [29].
In addition a significant change of the shear viscosity was observed in
Al2O3/polyacrylic acid (PAA) slurry (Scheme 1-4). This technology would be very
useful to decrease industrial slurry preparation since sometimes the slurry viscosity is
extremely high in high contents of inorganic powders. As demonstrated in similar
behavior in NIPAM copolymers, P(NIPAM-co-AA) with PAA showed sonorespond
behavior in aqueous medium (Scheme 1-5) [30, 31]. But, the increase of the shear
viscosity was also observed when the US exposure was stopped. These variations were
explicable by the breaking of hydrogen bonding of their polymers in the environment,
when the US exposure was performed in the medium. In addition, FT-IR measurements
of the aqueous solution strongly supported that carboxylic group in the
Al2O3/polyacrylic acid (PAA) slurry and NIPAM copolymers had breakage of the
hydrogen bonding by the US exposure. Since the behavior was observed cyclically with
and without US, the US exposure acted as a stimulating force to the change in the shear
viscosity of the solutions. Therefore, what will be needed in research of sonoprocess as
uses of US stimuli in the US effect on aqueous polymer systems. The demand in the
15
Chapter 1 Introduction
a)
b)
Scheme 1-3 a) chemical struture and b) SEM picture of NIPAM-AA-MBAA microgel
16
Chapter 1 Introduction
future research will be to represent the analysis of US on the absorption behavior in the
medium and on the detail for the US stimulation. On the basis of these pointed views,
studied sonoprocess for hydrogen bond breakage in aqueous polymer systems.
O
O
O H
H
H
H
H
O
O
H
O
O H
H
H
O
O
O
H
H
H
H
OH
O
H
H
H
H
O
O
chain
O
OH
P
O
O
O
OH
P
chain
O H
H
H
H
ithout
lO
O
HO
H
OH
OH
H
O
O
O
OH
H
H
O
O
O H
ith
O
O
OH
OH
H
O
O
OH
lO
O
OH
O
O
HO
H
OH
O
OH
O
O
O
Scheme 1-4 Influence of US upon hydrogen bond networks between Al2O3 and PAA.
Scheme 1-5 Chemical structure of NIPAM-co-AA
17
Chapter 1 Introduction
1.4 Scope of present investigation
In the present thesis, in order to clarify US effect on hydrogen bond crosslinking
polymers in aqueous medium, the analyzed results are summarized by following
chapters. Here is scope of the present investigation listed the chapter with a brief
description of the thesis contents. Chapter 1 has presented a brief introduction to
ultrasound applied in chemistry. Here are introduced concepts of ultrasound and
techniques used for the investigation in this thesis, especially for sonoprocess related
with polymer with soft matters. Besides, author has explained the importance of the US
as an external stimulus in in the chemical process. In Chapter 2, US effect in natural
polymers containing hydrogen bond crosslinkage in aqueous polymer solutions is
mentioned. Here polysaccharides such as agar, -carrageenan and -carrageenan are
used to analyze their aqueous viscosities before and after US exposure. The results
demonstrate that hydrogen bonds crosslinkage of the polysaccharides solutions can be
reduced by the US exposure. When the US stimulus is stopped, hydrogen bond can
re-from in the polymer. This is especially significant at the US frequency of 45 kHz.
The US effect is also proved with FT-IR analysis of the aqueous carrageenan medium.
Chapter 3 shows that Polyvinyl alcohol (PVA) having different molecular weights and
hydrolysis degrees is applied for US stimuli. It is found that physical and chemical
properties of PVA are highly related with the hydrogen bond in PVA aqueous solution.
18
Chapter 1 Introduction
The US frequency at 43 kHz shows inflently absorb in to the PVA solution. Therefore
new US absorption model is proposed in order to describe the US effect on the aqueous
PVA solution. It is observed that as increasing the molecular weight of the polymer is
observed, the US effect is more significant. Here, new US absorption model is applied
to anayze such US stimuli effect. In Chapter 4, it is investigated that the effect of
polymer functional group on viscosity of water soluble polymers, PAA, PVA and PEG
is studied. It is found that these polymers form hydrogen bond crosslinkage in aqueous
medium but the US especially at 43 kHz frequency makes a change in the shear
viscosity due to breaking hydrogen bonds by efficient ultrasound absorption. These
behavior also are supported by the explanation of the US absorption model for each
polymer system. In Chapter 5, US effect on thermo-sensitive PNIPAM/AA hydrogel is
investigated. The slightly crosslinked PNIPAM/AA hydrogels having sub-microsized
diameter exhibits the two step volumetric shrinking at around 24 ˚C and 36 ˚C.
However, after exposing the US, their shrinking temperatures are significantly changed
to be higher temperature side at 30 ˚C and 40 ˚C, respectively. FT-IR measurements in
the mixture of hydrogel and water are demonstrated that such change of the
intermolecular hydrogen bonding happened with in the US irradiation, since US can
break the hydrogen bonds between NIPAM and AA segments. In final Chapter 6,
19
Chapter 1 Introduction
conclusion of my doctoral thesis is summarized in addition with suggestions for future
works addressed by the US technology.
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Chapter 1 Introduction
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Chapter 1 Introduction
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use of ultrasound for improved industrial crystallization Org. Process Res. Dev., 9, 923–
932 (2005).
[22] S. de la Fuente-Blanco, E. Riera-Franco de Sarabia, V.M. Acosta-Aparicio, A.
Blanco-Blanco, J.A. Gallego-Juarez, Food drying process by power ultrasound,
Ultrasonics, 44 (2006) e523–e527.
[23] E. Riera-Franco de Sarabia, J.A. Gallego-Juarez, G. Rodrıguez-Corral, L.
Elvira-Segura, I. Gonzalez-Gomez, Application of high-power ultrasound to enhance
fluid/solid particle separation processes, Ultrasonics, 38 (2000) 642–646.
[24] Hyun-Jong Kim, H. Matsuda, H. Zhou, I, Honma, Ultrasound-triggered smart
drug release from a Poly(dimethylsiloxane)–Mesoporous silica composite Adv. Mater.,
18 (2006) 3083–3088.
22
Chapter 1 Introduction
[25] B. G. De Geest, A. G. Skirtach, A. A. Mamedov, A. A. Antipov, N. A. Kotov, S.
C. De Smedt, G. B. Sukhorukov, Ultrasound-Triggered release from multilayered
capsules Small, 3 (2007) 804 – 808.
[26] N Rapoport, Combined cancer therapy by micellar-encapsulated drug and
ultrasound. International Journal of Pharmaceutics, 277 (2004) 155-162.
[27] Isozaki, K., Takaya, H. and Naota, T., Ultrasound-Induced Gelation of Organic
Fluids with Metalated Peptides. Angew. Chem. Int. Ed., 46 (2007) 2855–2857.
[28] K.K. Latt, T. Kobayashi, TiO2 nanosized powders controlling by ultrasound sol–
gel reaction Ultrason. Sonochem., 15 (2008) 484–491.
[29] D. Huo, T. Kobayashi, Sonoresponsive volume phase-transition behavior of
crosslinked poly(N-isopropylacrylamide-co-acrylic acid). Microgel. Chem. Lett., 35
(2006), 776-777.
[30] N. L. Ngoc, T. Kobayashi, Ultrasound stimuli on viscometric change of aqueous
copolymers having acrylic acid and N-isopropyl acrylamide for thermo-sensitive
segments, Ultrason. Sonochem., 18, (2011) 1185-1192.
[31] N. L. Ngoc, T. Kobayashi, Ultrasound stimulus effect on hydrogen bonding in
networked alumina and polyacrylic acid slurry, Ultrason. Sonochem., 17, (2010)
186-192.
23
Chapter 1 Introduction
24
2 Chapter 2 Ultrasound Effect Used as External Stimulus for
Viscosity Change of Aqueous Carrageenans
Abstract
Ultrasound (US) serves as a stimulus to change shear viscosity of aqueous
polysaccharides of -carrageenan, -carrageenan, and agar. The US effect was
compared in their aqueous solutions at 60 ˚C for the US frequency of 23, 45, and 83
kHz. Under the US condition with 50 W at 45 kHz, the shear viscosity of each aqueous
solution was decreased significantly. Subsequently, when the US was stopped, the shear
viscosity returned back to the original value. In addition, the US showed different
effects of the US frequency over the viscosity change in the three kinds of
polysaccharides. When the US frequency was changed, the US effects were less at 83
kHz and 28 kHz for the shear viscosity change. In addition, as NaCl was present in the
aqueous solution, the viscosity change decreased by the US exposure. These results
suggest that the US effect on the viscosity reduction was influenced by the condition of
polymer coil conformation, which was expanded or shrank by electrostatic repulsion of
the SO3- groups. FT-IR analysis supported that the hydrogen bonds of carrageenans
were broken during the US exposure. Using Fourier self-deconvolution for the FT-IR
25
Chapter 2 Ultrasound effect on aqueous carrageenans
spectra without and with US exposure suggests that the US influenced the hydrogen
bonds of water and the OH group of polysaccharides.
2.1 Introduction
It has been well known that ultrasound (US) technique is applied in various fields such
as engineering, medicine and other processes. Generally, US resource becomes to be
mainly used to dissolve substances or homogenize mixtures at low-frequency. Therefore,
US technique has earned interest in their operations [1, 2]. Especially in sono-process,
US irradiation related to the extraction in food engineering [3, 4] and separation process
like a membrane [5, 6]. Also, few studies of smart materials have been developed in
ultrasound sensitive materials as external trigger, although sensitive external trigger
such as light, heat or electricity has been found [7]. In this case, US could behave as a
stimulus in volume phase-transition of copolymer microgels of N-isopropyl acrylamide
(NIPAM) and acrylic acid (AA) [8]. In addition, US irradiation significantly decreased
the shear viscosity of the copolymer aqueous solutions [9], indicating the breaking of
hydrogen bonding networks of the aqueous copolymer by lower frequency of US. In
similar behavior of the low frequency US, hydrogen bonds in aqueous PAA/Al2O3
slurry were influenced by the US exposure [10]. These might be due to US absorption
into the aqueous medium of hydrogen bonded polymers.
26
Chapter 2 Ultrasound effect on aqueous carrageenans
In contrast to these studies, the present work described US effect on aqueous viscosity
for industrial applications of carrageenans and agar. These are kind of linear
polysaccharides obtained from red seaweeds [11]. These polysaccharides exhibit a
gelation behavior at 30-45 ˚C. Therefore, there are many industrial uses for example in
jellies pudding of food industry and biotechnology. Especially -carrageenan and agar
are important polysaccharides, when the medium temperature increases they became in
viscous solutions [11−14] at over 60 ˚C. As shown in Scheme 2-1, chemical structure of
agar
consists
in
(1,3)-linked
β-galactopyranose
and
(1,4)-linked
(3,6)-anhydro-α-galactopyranose unit. In the case of -carrageenan, the repeated unit
consists
of
(1,3)-linked
galactopyranose
4-sulphate
and
(1,4)-linked
3,6-anhydrogalactopyranose residues and -carrageenan differs in the number of SO3group [11]. It is known that both carrageenans were widely used as food additives to
produce emulsion systems. Therefore, viscosity control of the viscous solution becomes
an important process in their industries and it was very beneficial to apply US for
decreasing viscous condition of polymer systems. Therefore, the advanced effect of US
would be important in such industrial fields, but, such US effect on aqueous
polysaccharides has not been known well yet. So, aqueous carrageenans and agar were
used to study the US effect on the viscosity changes in aqueous solution. The US effect
27
Chapter 2 Ultrasound effect on aqueous carrageenans
Scheme 2-1 Chemical structures of a) -carrageenan, b) -carrageenan, and c) agar.
28
Chapter 2 Ultrasound effect on aqueous carrageenans
compared polysaccharides in their aqueous solution,  and  carrageenans and agar was
measured, for this study using US at different frequencies of 28, 45 and 83 kHz.
2.2 Experimental
2.2.1 Materials
Polysaccharides such as -carrageenan and -carrageenan were purchased from TCI Co.,
Ltd (Japan) and agar from Nacalai Tesque Co., Ltd (Japan). All the chemicals were used
without further purification. Each polysaccharide was used to prepare aqueous solutions
dissolving in hot water at 80 ˚ and the powdered sample was continuously stirred by a
magnetic stirrer.
queous solutions of κ-carrageenan, ι-carrageenan, and agar were
prepared with 3 wt. % concentration in a glass vessel (diameter: 40 mm, height: 120
mm, and thickness of 0.14 mm) and used for the measurements of the shear viscosity.
Water used to prepare solutions was distilled and purified using an ion exchange
column.
2.2.2 Measurements of shear viscosity of aqueous polysaccharides.
Figure 2-1shows the measure setup of ultrasonic bath (Ultrasonic Multi Cleaner W115,
Honda Electronics Co., Ltd 30×30×30 cm3) with seven piezoelectric pieces of 3 cm of
diameter on the side wall. The bath was connected to a controller, which can produce
different frequencies 28, 45, and 83 kHz with an input power in the range of 200-300
W.
29
Chapter 2 Ultrasound effect on aqueous carrageenans
The temperature was measured with a Digital Thermo Hygrometer (Custom, CTH-1365)
and controlled through whole experiments in the water bath by using a type immersion
heater (Hakko, Japan). Then, the voltage was controlled with an alternate current
voltage adjustment machine (Tokyo-Rikosha Co. LTD., Slide Transform RSA・RSC
Series) was calibrate to give a temperature out of 60 ˚ in the submergible heater.
A calorimetric study was carried out to determine the dissipated power in the water bath
[15]. The dissipate power of each frequency was controlled at 50 W in the water bath.
All of the experiments were carried out at 60 °C in order to get a viscous aqueous
solution. The shear viscosity was measured before and after the US operation by a
Brookfield viscometer rotating cylinder (Tokyo Keiki Inc.). The sample vial containing
the aqueous carrageenan or agar solution was set in the ultrasonic bath before the US
irradiation for about an hour at 60 ˚ . The US exposure was carried out for 5 min and
then, the US was turned off. After US was stopped, immediately the shear viscosity was
measured with 1 min interval. Until, the value of the shear viscosity returned back to the
original value. Sample solutions were similarly exposed to the US during 5 min each at
frequency of 28, 45 and 83 kHz. The rotation of the Brookfield type viscometer was 60
rpm at 60 ˚C with rotor No 2. In order to confirm the US effect on the degradation of
polysaccharides, HPLC profiles were measured and compared before and after the US
30
Chapter 2 Ultrasound effect on aqueous carrageenans
Figure 2-1 Scheme of the experimental setting for the measurement of the shear
viscosity in polysaccharides solutions with US exposure.
31
Chapter 2 Ultrasound effect on aqueous carrageenans
exposure at different frequency. In the experiment, HPLC system (CCPS, Tosoh Corp),
equipped with UV detector (UV 800, system Instruments Co., Ltd) and TSKgel 5000
column was used. The polysaccharides profiles before and after the US exposure were
obtained without change in the chromatograms. This indicated that no degradation of
the polysaccharides was confirmed by the US exposure at 50 W for 5 min of exposure.
2.2.3 Determination of US effect on FT-IR spectra of the polysaccharide solutions
To determine chemical changes of the polysaccharides solutions, FT-IR spectra were
measured on a JASCO FT-IR/4100 spectrometer using two CaF2 plates with diameter
30 mm and thickness 2 mm (Pier Optics Co. Ltd.). As shown in the Scheme 2-2, on one
side of the plate, a small amount of polysaccharide solution with 3 wt. % concentration
was dropped. Then, the other plate was press to cover the dropped solution; thereby, a
thin layer of the polysaccharide was produced between the two plates. In order to
prevent water penetration into the sample layer, the CaF2 overlapping windows were
sealed with Teflon tape (0.1 mm×13 mm, Sanyo, Japan), and it were exposed to US in
the water bath. FT-IR spectra of the polysaccharides solutions were measured using
absorbance mode after 1, 3, and 5 min of US exposure. In the FT-IR spectra analysis for
the OH stretching band, the fixed positions were determined using Fourier self
deconvolution for curve fitting [16, 17]. These spectra on the wetting films were
32
Chapter 2 Ultrasound effect on aqueous carrageenans
Scheme 2-2 Preparation sample for FT-IR measurement and US exposure setting.
33
Chapter 2 Ultrasound effect on aqueous carrageenans
compared with those of the dry films. The dry films on the CaF2 windows were
prepared dropping a small amount of the aqueous solution and then dried with a dryer
until no change in the FT-IR spectra was observed.
2.3 Results and discussion
2.3.1 Effect of ultrasound on shear viscosity of polysaccharides solutions
Figure 2-2 shows time change of the shear viscosity of the polysaccharide aqueous
solution containing a) -carrageenan, b) -carrageenan and c) agar. The concentration of
each polysaccharide was fixed on 3wt% and temperature was 60 ˚C for the US
treatment. Before the sample was exposed to each US, the shear viscosity was measured
at time zero. The sample was exposed to the US for 5 min at different frequencies with
50 W. Figure 2-1 illustrates the experimental setting for the measurement of the US
water bath including B type viscometer. The measurements of the shear viscosity were
carried out after the US was stopped. Every minute, the values of shear viscosity value
were measured. It was observed that the shear viscosity significantly decreased after the
US exposure in each solution. However, the tendency of the decrease values of the shear
viscosity changed in the case of the polysaccharide. The case of -carrageenan showed
that only 45 kHz frequency was effective in the viscosity change. The others
frequencies of 28 and 83 kHz show no change in the shear viscosity after the US was
exposed. For -carrageenan, the 83 kHz US showed also no change in the shear
34
Chapter 2 Ultrasound effect on aqueous carrageenans
viscosity, but both USs having 45 and 28 kHz showed a decline in the value of the shear
viscosity. It was noted that the chemical structure of  and  carrageenans showed
different contents of SO3- group in the polymer unit. Here, -carrageenan contained two
SO3- groups and k-carrageenan had one SO3- group in the chemical structure (Scheme
2-1). Therefore, we compared the aqueous agar solution with no SO3- groups in the
change of the shear viscosity (Figure 2-2 (c)). The decline degree of the shear viscosity
in the agar solution was observed in the order of 45, 28, and 83 kHz for each US
frequency. It was noted that the decreased values of the shear viscosity returned to its
original value after 5 minutes. When the US was stopped, the viscosity was measured
without US operation and the measurement of viscosity was continued for 5 min. After
the first cycle finished with the return to the original value, the US exposure was again
performed for 5 min. In each case, similar change of the shear viscosity was observed in
the second cycle. These meant that the US stimulated the change in the shear viscosity
of polysaccharides solutions and the change was occurred reversibly. In addition, the
US stimulation was influenced by the existent numbers of the of SO3- groups in the
chemical structure of the polysaccharide. Especially, carrageenans solutions showed
less effect of the US at 83 kHz. To study the effect of SO3- group on the viscosity, the
shear viscosity of the carrageenans and agar solution containing 1 wt% of NaCl
35
Chapter 2 Ultrasound effect on aqueous carrageenans
Figure 2-2 Shear viscosity without and with US exposure at 50 W for a) -carrageenan,
b) -carrageenan and c) agar.
36
Chapter 2 Ultrasound effect on aqueous carrageenans
concentration was determined similarly. Figure 2-3 shows changes in the shear viscosity
for each polysaccharide in presence of NaCl. Here, the salt can shield the electrostatic
repulsion of SO3- groups of the carrageenan segments to expand the polymer chains
[18-20]. When NaCl was present in the aqueous carrageenans solution, the values of the
shear viscosity decreased from 540 cP to 490 cP and 500 cP to 480 cP, respectively, for
 and  carrageenans. But the shear viscosity of the aqueous agar was no change in the
absence and presence of the NaCl. The tendency of the shear viscosity on the US
exposure was similar to that observed in the salt-free solutions in the case of agar
solution. In these cases for NaCl systems, still no US changes in the shear viscosity for
-carrageenan at 28 and 83 kHz and -carrageenan at 83 kHz. But, in other cases the US
could make viscosity changes in the aqueous solution containing NaCl. These
comparisons indicate that the US effect on the viscosity also influenced the polymer coil
conformation. Results suggest that the aqueous carrageenan solution absorb US power,
this could be due the sound energy in the polymer molecules might break hydrogen
bonds of the polymers especially at 45 kHz.
2.3.2 Measurement of US effect on FT-IR spectra of polysaccharide solutions
It is known that FT-IR spectrometry can provide useful information of polymeric
37
Chapter 2 Ultrasound effect on aqueous carrageenans
Figure 2-3 Shear viscosity without and with US exposure at 50 W for a) -carrageenan,
b) -carrageenan, and c) agar in presence of NaCl. (Dot line 45 kHz without NaCl).
38
Chapter 2 Ultrasound effect on aqueous carrageenans
hydrogen bond network [21]. Thus, aqueous polysaccharide solution affected by US,
the FT-IR spectra of the -carrageenan -carrageenan and agar solution were measured
and compared before and after the US exposure. Figure 2-4 shows the FT-IR spectra of
dried film and aqueous film of -carrageenan, -carrageenan, and agar. The FT-IR
spectra showed the distinctive bands appeared in the region of 3000−3800 cm-1 for the
OH stretching bands [22]. In the wide stretching band, the non-hydrogen bond or free
hydroxyl group could absorb strongly in the 3700-3400 cm-1 region and hydrogen bond
interactions appeared in 3400-3000 cm-1. The band detected in 3000-2800 cm-1 denoted
the stretching C-H for the alkyl groups of the carrageenans. The band at 1700-1400 cm-1
corresponded to the carboxyl-methyl group. From the wavenumber region in 1400-1000
cm-1 the vibration band of the SO3- group was assigned. The peak at 1320 cm-1 and 1150
cm-1 corresponded to SO2 asymmetric stretching. The peak at 1170 cm-1 was assigned to
-COC-groups and the one at 1070 cm-1 was attributed to the glycosidic bonds [22-24]. It
was also seen that a small difference was also observed between the dry and wet film
for the region at 3800-2600 cm-1 region. Therefore, we analyzed the hydration
phenomenon of the polysaccharides by peak deconvolution in the FT-IR spectra. From
the data of the dried films and aqueous films, the peak positions were determined using
second derivative method. These spectra were decomposed into Gaussian components
39
Chapter 2 Ultrasound effect on aqueous carrageenans
Figure 2-4 FT-IR spectra of a) -carrageenan, b) -carrageenan and c) agar.
(Dot line dry film. Solid line wet film).
40
Chapter 2 Ultrasound effect on aqueous carrageenans
by curve fitting with fixed positions [16, 17]. The results of peak positions are presented
in Table 2-1. Here, the peaks 1, 2 and 3 were assigned to water molecules strongly
bonded with free OH group of the polysaccharide chain with intermolecular bonding,
and that of the chain bonding with another neighbor OH group, respectively [22, 25].
Peak 4 was assigned to free OH groups of the polysaccharides chains. Peaks 5 and 6
were assigned to weak bonds of water and free water molecules respectively [25].
Scheme 2-3 shows the illustration of the OH group of the polysaccharides. As shown in
Figure 2-5, the peak position of the dried films and aqueous films included the
deconvolution data for the hydration phenomenon. It was observed that after a little
water drop was placed in the film, the dry peak 1 increased its intensity for
-carrageenan and -carrageenan cases. However, in the case of agar for the wet sample
no significant change was observed. This indicated that the SO 3- groups in the
carrageenan enhanced water accessibility of the polysaccharides films. Also, the
intensity of the peak 2 it seemed to decrease in all the cases. As a consequence of the
water addition, the intermolecular hydrogen bonding of the OH group of the
polysaccharide was broken. The band intensity of the peaks 1 and 3 increased. For the at
45 kHz US exposure. It was observed that the after US exposure for 1, 3 and, 5 min, the
intense of the OH band became higher. In case b) for the results of deconvolution of
41
42
Dry -c
3219
3301
3410
3514
3550
3601
Peak
index
1
2
3
4
5
6
3615
3567
3491
3395
3318
3214
Dry -c
3611
3512
3407
3321
3214
Dry Agar
3592
3522
3452
3380
3285
Wet -c
3616
3569
3509
3397
3314
3213
Wet -c
3615
3521
3392
3330
3200
Wet Agar
3611
3554
3487
3388
3289
3193
5 min -c
Table 2-1 Center of the peak wavenumber determined with Curve-fitting for the OH stretching band.
3620
3572
3499
3396
3315
3222
5 min -c
3641
3587
3545
3442
3276
3239
5 min
Agar
Chapter 2 Ultrasound effect on aqueous carrageenans
Scheme 2-3 Suggestible Structure of Hydration of a -carrageenan molecule.
Chapter 2 Ultrasound effect on aqueous carrageenans
43
Absorbance
3700
3600
6
3400
Wavenumber
3500
3
3100
3000
6
eagar ry Film
3200
0
3800
3700
3600
6
Wavenumber [cm-1]
3800 3700 3600 3500 3400 3300 3200 3100 3000
0
0.05
0.1
0.15
0.2
0.25
[cm -1 ]
3300
0.05
0.1
0.15
0.2
0.25
c-carragenan ry Film
3400
3300
Wavenumber [cm -1 ]
3500
3
Figure 2-5 Deconvolution of the OH stretching region of -carrageenan, -carrageenan, and agar
(a, c, and, e dry film for each case and b, d, and f wet film for each case).
0
3800
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Absorbance
44
Absorbance
a-carragenan ry Film
3200
3100
3000
Chapter 2 Ultrasound effect on aqueous carrageenans
Absorbance
0
3800
0.05
0.1
0.15
0.2
0.25
0.3
0.35
3700
3600
6
3400
3300
3200
3700
fagar
3800
0
0.05
0.1
0.15
0.2
0.25
Wavenumber [cm-1 ]
3500
3
Absorbance
et Film
3000
3600
3300
[cm-1]
Wavenumber
0
3800
3400
3500
et Film
3100
0.05
0.1
0.15
0.2
0.25
3200
3700
d-carragenan
Absorbance
b-carragenan
3100
3400
3
3300
Wavenumber [cm-1 ]
3500
3000
3600
6
et Film
3200
3100
3000
Chapter 2 Ultrasound effect on aqueous carrageenans
45
Chapter 2 Ultrasound effect on aqueous carrageenans
peak 3 was no change in the -carrageenan. But, for -carrageenan and agar, the band
intensity increased in the presence of water. In case a) for Figure 2-6, 2-7, and 2-8, the
changes of the FT-IR spectra were observed for -carrageenan, -carrageenan and agar
the OH band after 5 min of US exposure, the components of the peaks 1 and 3 appeared
in all polysaccharides used. It seems that the US enhanced the interactions between
water and polysaccharides by intramolecular hydrogen bonding. Although the peak 2
decreased, this meant that the US easily affected the intermolecular interactions. It was
noted for the peak 4 that the deconvoluted band intensity of the carrageenans increased
by the US exposure. Because the intermolecular interactions were broken by the US, the
water molecules were included in the polysaccharide molecules to interact in other ways.
On other hand, in Figure 2-8 (b), the agar spectra presented that the peak 3 was
enhanced by the US exposure. These comparisons of the deconvolution strongly
indicated that the presence of the SO3- group preferred to form free OH group of agar
by the US exposure. Figure 2-9 shows the relation of the OH intensity after the
exposure of US at different times for the FT-IR samples. It was noted that the OH band
intensity, It/IO, was observed to increase in each polysaccharide, when the exposure
times were increased from 1 min to min. This supported that the OH band intensity was
influenced by the US exposure. In addition, the 45 kHz US was effective for the
46
Chapter 2 Ultrasound effect on aqueous carrageenans
a
exposure
Absorbance
0.45
0.4
5 min of US
0.35
3 min of US
1 min of US
0.3
No US
0.25
0.2
0.15
0.1
0.05
0
3800
3400
3000
2600
2200
1800
1400
1000
3100
3000
Wavenumber [cm-1]
b
econvolution
0.45
min of
0.4
Absorbance
0.35
0.3
0.25
0.2
3
6
0.15
0.1
0.05
0
3800
3700
3600
3500
3400
3300
3200
Wavenumber [cm-1]
Figure 2-6 FT-IR spectra of -carrageenan at 45 kHz without and with US exposure.
a) Different time of US exposure. b) Deconvolution after 5 min of US exposure.
47
Chapter 2 Ultrasound effect on aqueous carrageenans
a
exposure
0.35
0.3
5 min of US
3 min of US
Absorbance
0.25
1 min of US
0.2
No US
0.15
0.1
0.05
0
3800
3400
3000
2600
2200
1800
1400
1000
Wavenumber [cm-1 ]
b econvolution
0.35
0.3
Absorbance
0.25
0.2
0.15
3
0.1
6
0.05
0
3800
3700
3600
3500
3400
3300
3200
3100
3000
Wavenumber [cm-1]
Figure 2-7 FT-IR spectra of -carrageenan at 45 kHz without and with US exposure.
a) Different time of US exposure. b) Deconvolution after 5 min of US exposure.
48
Chapter 2 Ultrasound effect on aqueous carrageenans
a
exposure
0.3
5 min of US
3 min of US
0.25
Absorbance
1 min of US
No US
0.2
0.15
0.1
0.05
0
3800
3400
3000
2600
Wavenumber
2200
1800
1400
1000
[cm-1]
b econvolution
0.35
min of
0.3
Absorbance
0.25
0.2
3
0.15
6
0.1
0.05
0
3800
3700
3600
3500
3400
3300
3200
3100
3000
Wavenumber [cm-1]
Figure 2-8 FT-IR spectra of agar at 45 kHz without and with US exposure. a) Different
time of US exposure. b) Deconvolution after 5 min of US exposure.
49
Chapter 2 Ultrasound effect on aqueous carrageenans
a-carragenan
1.2
45 kHz
It/I0
23 kHz
86 kHz
0.98
0
1
2
3
4
5
4
5
4
5
Time Exposure [min]
b-carragenan
1.2
45 kHz
23 kHz
It/I0
86 kHz
0.98
0
1
2
3
Time Exposure [min]
cagar
1.2
45 kHz
It/I0
23 kHz
86 kHz
0.98
0
1
2
3
Time Exposure [min]
Figure 2-9 Change in the OH stretching intensity with different US time exposure.
50
Chapter 2 Ultrasound effect on aqueous carrageenans
enhancement of the OH band related with hydrogen bonded networks of polysaccharide.
2.4 Conclusion
In the present work, the US effect was studied in aqueous carrageenan solutions
measuring the shear viscosity at 60 ˚C. The experiments focused in the hydrogen bond
interactions, and showed that the aqueous solution of polysaccharides responded to the
US stimulus. On other hand, the recovery of the shear viscosity was also observed,
when the US exposure stopped. This could be indicated reversible change by the US
exposure. In addition, the presence of SO3- groups in the polysaccharides suppressed the
US effect, especially in 23 and 83 kHz US for -carrageenan and 83 for -carrageenan.
FT-IR spectroscopy suggested that the US broke the hydrogen bonded networks of the
polysaccharides and then, water molecules were re-distributed into the OH groups of the
carrageenans.
References
[1] G. J. Price, In. Chemistry under extreme or non-classical conditions; Rvan Eldik,
E. D., Hubbard, C. C., New York: Wiley& Sons, (1996).
[2] T. J. Mason, J.P. Lorimer, Applied Sonochemistry, The uses of power ultrasound
in chemistry and processing, Wiley-VCH Verlag GmnH, Weinheim (2002)
[3] T. J. Mason, L. Paniwnyls, J. P. Lorimer, Ultrason Sonochem., 3(1996), pp.
s253-s260.
. Chermat, N. Hoarau, Ultrason. Sonochem., 11 (2004) pp. 257-260.
51
Chapter 2 Ultrasound effect on aqueous carrageenans
[5] K. K. Latt, T. Kobayashi, Ultrason. Sonochem., 13(2006) pp. 321-328.
[6] X Chai, T. Kobayashi, N. Fujii, J. of Membrane Science, 148 (1998) pp. 129-135.
[7] D. Roy, J. N. Cambre, B. S. Sumerlin, Progress in Polymer Science., 35 (2010) pp.
278–301.
[8] D. Huo, T. Kobayashi, Chem. Lett., 35 (2006) pp. 776-777.
[9] N. L. Ngoc, T. Kobayashi, Ultrason. Sonochem., 18 (2011) pp. 1185-1192
[10] N. L. Ngoc, T. Kobayashi, Ultrason. Sonochem., 17 (2010) pp. 186-192.
[11] Peter A. Williams, Handbook of Industrial Water Soluble Polymers, Blackwell
publishing, (2007).
[12] M. Toubal, B. Nongaillard, E. Radziszewski, P. Boulenguer, V. Langendorff,
Journal of Food Engineering, 58 (2003) pp. 1–4.
[13] M.Audebrand, J.L.Doublier, D.Durandl and J.R.Emeryl, Food Hydrocolloid, 9
(1995) pp 195-203.
[14] Jong-Rim Bae, Journal of the Korean Physical Society, 55 (2009) pp. 241624-19.
[15] Ratoarinoro, F. Contamine, A.M. Wilhelm, J. Berlan and H. Delmas, Ultrason.
Sonochem., 2 (1995) pp. s43–s47.
[16] H. Kitano, K. Ichikawa, M. Ide, M. Fukuda,
Langmuir, 17 (2001) pp.
1889-1895.
[17] H. Kitano, M. Ide, T. Motonaga,
Langmuir, 22 (2006) pp. 2422-2425.
[18] M. Watase, K. Nishinari, Rheol. Acta, 21 (1982) pp. 318-324.
[19] C. Michon, G. CuveIier, B. Launaya A. Parker, Carbohydrate Polymers, 331
(1996) pp. 161-169
[20] M. Watase, K. Nishinari, Colloid & Polymer Sci., 260 (1982) pp. 971-975.
52
Chapter 2 Ultrasound effect on aqueous carrageenans
[21] B. Stuart, Infrared Spectroscopy: Fundamentals and Applications. Wiley, New
York, 2004
[22] B. Matsuhiro, Hydrobiologia, 326/327 (1996) pp. 481-489.
[23] M. Kacurakova, R.H. Wilson, Carbohydrate Polymers 44 (2001) pp. 291-303.
[24] J. Prado-Fernández, J. . Rodrıguez-Vázquez, E. Tojo, J.M. Andrade, Analytica
Chimica Acta, 480 (2003) pp. 23-37.
[25] T. Singh, R. Meena, and A. Kumar, J. Phys. Chem., B113 (2009) pp. 2519–2525.
53
Chapter 2 Ultrasound effect on aqueous carrageenans
54
3 Chapter 3 Ultrasound Stimulus Inducing Change in
Hydrogen Bonded Crosslinking of Aqueous Polyvinyl
Alcohols
Abstract
The effect of ultrasound (US) stimulation on the shear viscosity of aqueous polyvinyl
alcohol (PVA) solution was studied when the solution was exposed to US at 23, 43, 96,
and 141 kHz. The US stimulus showed a marked decrease of the shear viscosity of the
solution in the order of 43>96>23>141 kHz, respectively, under US power dissipation
of 8.5 8.9, 8.9, and 8.8 W. Subsequently, when US exposure was stopped, the shear
viscosity of PVA reverted to its original value. The US stimulation was analyzed with
the US power transmitted through the PVA aqueous media. Furthermore, FT-IR spectra
measured at different durations of US exposure, suggest that hydrogen bonds in the
PVA segments were broken by the US exposure. We conclude that structural changes of
the hydrogen bonded crosslinks of PVA were induced to include water molecules for
the re-forming of crosslinks of aqueous PVA.
3.1 Introduction
Intelligent materials of many kinds have been developed with properties that can be
changed considerably by an external stimulus such as light, heat, or electricity.
55
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
Extension of these technologies to several applications has been reported [1], because
such materials can respond to external signals and can induce a distinct reaction to the
outer environment. The well-known ultrasound (US) technique has been applied in
various fields such as engineering and medicine. The US transmitted through any
substance, influences several properties of materials. Low-frequency US, which shows
effectiveness with common applications, is used mainly to dissolve substances or to
homogenize mixtures. In addition, US has earned interest for use in various operations
for de-gasification and particle size reduction [2, 3]. For food engineering [4, 5],
sonochemical effects of high-frequency US have been applied to degradation of organic
material [6]. Using US triggers, our previous works have demonstrated that US can
serve as an external stimulus in copolymer microgels of N-isopropylacrylamide
(NIPAM) and acrylic acid (AA) using methylenebisacrylamide as a crosslinker [7]. The
exposure of spherically polymeric microgels to US changed the hydrodynamic diameter
in water medium and also the volume phase-transition temperature of NIPAM
microgels. In addition, under the US environment, a perceptible change of the shear
viscosity was observed in Al2O3/ polyacrylic acid (PAA) slurry and NIPAM copolymers
with PAA in each aqueous medium [8, 9]. These were attributable to the breaking of
hydrogen bonding crosslinks of their polymers under US exposure in aqueous medium.
56
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
Regarding the decrease of shear viscosity from US exposure, US absorption might have
induced polymer change, especially in hydrogen-bonded crosslinks. To date, absorption
coefficients and velocities for different non-ionic polymers solutions such as
poly(ethylene glycol(PEG)) and PAA have been reported for high-frequency US of
2–130 MHz [10-15]. However, reports have described no results for lower frequency. It
remains unclear, whether a substantial decrease of the shear viscosity was induced by
US exposure to aqueous medium or not, because US could affect the aqueous polymeric
systems which contain hydrogen bonding. The present study examined the viscosity
properties of polyvinyl alcohol (PVA) after exposure to US with different frequencies.
In fact, PVA is one of the most widely water soluble polymers used in the industry and
also widely study, because their properties can be approach in many fields such as
emulsifier, stabilizer for colloid suspensions, coating in the textile, and as an adhesive.
Its mechanical properties are strongly linked to the molecular weight and the degree of
hydrolysis, the reason of its behavior is due to the hydrogen bond interactions [16-20].
Therefore, US effects observed in this study are expected to be meaningful for industrial
applications. For this study, PVA of four molecular weights were chosen to analyze US
effects on the shear viscosity of the aqueous solution using US stimulus of 23, 43, 96,
57
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
and 141 kHz. The US effects on the PVA aqueous solution were observed using FT-IR
spectroscopy and observations of shear viscosity.
3.2 Experimental
3.2.1 Materials and sample solution preparation
The following detailed information is related to all PVAs used in experiments. The four
PVAs showed different molecular weight of 13000–21000, 31000–50000, 8200–85000,
and 75000 named, respectively, PVA13, PVA31, PVA217, and PVA117. PVA13,
PVA31, and, PVA217 had similar hydrolysis degrees in the range 86–88%. PVA117
had a hydrolysis degree of 98-99%. PVA13 and PVA31 were purchased from
Sigma-Aldrich; PVA217 and PVA117 were supplied by Kuraray Co. Ltd. (Japan).
Water used to prepare PVA solutions was distilled and purified using an ion exchange
column. In the cases of PVA217 and PVA117, because their high molecular weights,
these solutions were heated at 60 ˚ to be totally dissolved and the obtained transparent
solutions were slowly cooled to room temperature and kept at this temperature for one
night to settle eliminate air bubbles. Each aqueous PVA solution was prepared with 15
wt% concentration.
3.2.2 Ultrasound equipment and its evaluation.
A sonoreactor device (HSR-305R; Honda Electronics Co. Ltd., Japan) was used.
Scheme 3-1 shows a side view of the sonoreactor. A stainless steel water bath
58
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
Scheme 3-1 US experimental setting for the measurement of the shear viscosity in
polymer solution.
59
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
(8.5×13.5×13 (cm3)) had a 3-cm-diameter transducer on the side wall. The US
frequencies were 23, 43, 96, and 141 kHz with different variable intensities of 10–50 W,
which were controlled with a wave factory (WF1943B multifunction synthesizer; NF,
Japan). A calorimetric study was carried out to calculate the power dissipated in the
water bath [21-23]. The temperature (T) was recorded against time (t) at 300 s intervals
using a thermocouple placed in the middle of the water bath. From the T versus t data,
the temperature rise at zero time, T/t, can be estimated by constructing a tangent to
the curve or by curve-fitting the data to a polynomial in t. The ultrasonic power
dissipated entering to the system was determined by substituting the value of T/t into
Equation (1).
(3.1)
where Cp is the heat capacity of water (4200 Jkg-1K-1); m represents the mass of the
solvent used (kg). Figure 3-1 shows the dissipated and input US power at different
frequencies of 23, 43, 96, and 141 kHz. These data show that the input power can be
adjusted by controlling the dissipated power between 10–50 W for almost zero to 6–25
W. Results show that the power dissipated in the US water bath was 8.5, 9, 8.7, and 8.8
W for respective power values of 50, 35, 35, and 25, respectively, for 23, 43, 96, and
141 kHz. We used 8.5–9 W for comparison of US effects of different frequencies.
60
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
30.00
Dissipated power [Watts]
25.00
141 kHz
20.00
96 kHz
43 kHz
15.00
23 kHz
10.00
5.00
0.00
0
5
10
15
20
25
30
35
40
45
50
55
Input Power [Watts]
Figure 3-1 Dissipated power for all of the US frequencies used.
61
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
3.2.3 Shear viscosity measurement of PVA aqueous solutions
The Scheme 3-1 shows the measurement setup, includes a Brookfield rotating
viscometer (Tokyo Keiki Inc.), which facilitates shear viscosity measurements in the
water bath after the aqueous PVA solution was exposed to US. The shear viscosities of
the aqueous solution obtained before and after the US exposure were compared by
measurement with rotor No. 2. Here, the concentrated PVA solution was put in a
cylindrical glass vessel (40 mm diameter, 120 mm height) and set into the sonoreactor
water bath. The water bath temperature was maintained at 25 °C by flowing water
during the experiments. Measurements of the shear viscosity of the aqueous solution
were taken with and without the US exposure. Sample solutions were exposed in the US
environment during 5 min for each frequency at fixed US power dissipated of 8.5, 8.9,
8.9, and 8.8 W, respectively, for 23, 43, 96, and 141 kHz. After the US was stopped,
viscosity measurements were carried out at every minute until the shear viscosity
reverted to the original value. A similar experiment was conducted twice using the same
solution. The concentrations of the PVA solution used for the experiments were chosen
base on the fact that the hydrogen bond interaction at dilute and semi dilute solution are
ruled for the intermolecular interaction, but at high concentration the PVA aqueous
solution could form intermolecular and intramolecular interaction [16-20]. For this
62
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
reason the study was performed at higher concentration, because hydrogen bond
interaction could be broken by the US.
3.2.4 Measurements of US effects on FT-IR spectra of the aqueous PVA solutions
To ascertain US effects on the chemical changes of the PVA solution, we also measured
FT-IR spectra (FT-IR 4100 series; Jasco Corp.) of the PVA solution using two CaF2
plates (30 mm diameter; thickness 2 mm; Pier Optics Co. Ltd.). On one side of the plate,
a small amount of PVA solution with 25 wt% concentrated was dropped. Then, the
other plate was press to cover the dropped solution, thereby producing a thin layer
between the two plates. To prevent water penetration into the sample layer in the water
bath, the CaF2 plates were sealed with parafilm when they were exposed to US. FT-IR
spectra of the PVA solutions were measured immediately using absorbance mode after
1, 3, and 5 min of US exposure. In FT-IR spectral analysis for the OH stretching band,
the fixed positions were determined from their second derivatives for curve fitting [24,
25] using Peak Fitting option from Origin 8.5 software.
3.3 Results and discussion
3.3.1 Change in the shear viscosity of aqueous PVA during US exposure
Using US at almost equal power dissipation, the aqueous PVA solution in the water
bath was exposed for 5 min. The shear viscosity of the solutions was measured
63
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
subsequently at 1 min intervals.
Figure 3-2 shows plots of the values of the shear
viscosity obtained after the exposures. Experiments were performed after US was
stopped. As shown there, after 43 kHz US exposure, the shear viscosities decreased
significantly from their original values of 142, 375, 7700 cp, and
21000 cp, for a)
PVA13, b) PVA31, c) PVA217, and d) PVA117, respectively, to 124.5, 344, 6550 cp,
and 16750 cp. After the US exposure, each value of the shear viscosity value returned to
their original values. Those cases using 43 kHz US took about 20–35 min for reversal to
the original value. After the shear viscosity reversion, the aqueous solution was exposed
similarly to the US with a second time for additional 5 min in each PVA case. The time
course of the shear viscosity change is shown on the right side in
Figure 3-2. Similar
behavior was observed in the viscosity changes. The shear viscosity change that
occurred the first and second times implied that the US exposure acted as a trigger to
induce the change of the PVA shear viscosity. At different US frequencies, observations
revealed that 43 kHz US was effective for decreasing the shear viscosity relative to
other cases this demonstrates that the order of the decline was 43, 96, 23, and 141 kHz.
Furthermore, the US effect on shear viscosity was more pronounced at higher molecular
weight of PVA, which might be true, because higher crosslinkage of the polymer chains
showed more viscous properties. Comparison of the viscosity change in each PVA
64
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
solution at the same frequency showed an enhanced tendency: for example, at 43 kHz,
the change from 7700 cp to 6550 cp was more prominent in the PVA217. Results
suggest that the highly viscous solution can absorb the US power to lower the viscous
condition.
As shown in
Figure 3-2 for d) PVA117, it was observed that the shear
viscosity has also noteworthy decreased, even for the 141 kHz. These might be
explained, because the full hydrolysis degree of the PVA. It could be concluded that as
the molecular weight and the hydrolysis degree increases, the US absorption also
increases. Through US experiment water was circulated by pumping in the sonoreactor
and kept at 25 ˚C. The present study reveals that the US absorption could be observed at
low frequencies 23-141 kHz. We measured the extent of the decline of US profiles
directly and compared conditions before and after the US passed through the viscous
PVA solution.
3.3.2 Effect of US absorption on the PVA aqueous medium
To analyze US absorption by the aqueous PVA, the transmittance of US through the
PVA solution was investigated using a US detector to measure the US intensity.
Figure 3-3 shows the time profiles monitored at 43 kHz US in the absence and the
presence of PVAs. Here, the US intensity was attenuated from I0 to IUS magnitude,
when US passed through the sample medium of the glass cell for L=30 mm with 60 ml
65
b P
Shear viscosity [Cp]
380
375
370
365
360
355
350
345
340
3
122
126
130
134
138
142
3
0
0
5
5
10
15
10
Time [min]
ycle
Time [min]
ycle
20
15
25
20
43 kHz
96 kHz
23 kHz
141 kHz
30
43 kHz
96 kHz
23 kHz
141 kHz
Shear viscosity [Cp]
380
375
370
365
360
355
350
345
340
122
126
130
134
138
142
0
0
5
5
10
15
10
Time [min]
ycle
Time [min]
ycle
20
15
25
20
43 kHz
96 kHz
23 kHz
141 kHz
30
43 kHz
96 kHz
23 kHz
141 kHz
Figure 3-2 Change of shear viscosity for the aqueous a) PVA13, b) PVA31, c) PVA217, and d) PVA117 with 15 % concentration.
The US power dissipated was 8.5-9.
Shear Viscosity [Cp]
66
Shear Viscosity [Cp]
a P
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
d P
Shear Viscosity [Cp]
Shear Viscosity [Cp]
0
0
5
5
10
15
20
25
25
30
16500
15
20
30
Time [min]
35
43 kHz
96 kHz
23 kHz
18500
17500
141 kHz
10
ycle
Time [min]
35
43 kHz
19500
20500
21500
6400
6600
96 kHz
23 kHz
7000
6800
141 kHz
7200
7400
7600
7800
ycle
Shear Viscosity [Cp]
Shear Viscosity [Cp]
c P
16500
17500
18500
19500
20500
21500
6400
6600
0
0
5
5
10
15
20
25
25
30
10
20
Time [min]
15
ycle
Time [min]
30
35
43 kHz
96 kHz
23 kHz
141 kHz
35
43 kHz
96 kHz
23 kHz
7000
6800
141 kHz
7200
7400
7600
7800
ycle
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
67
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
total volume of the aqueous PVA with different PVA concentrations. The US intensity
decreased from I0 to IUS in the aqueous PVA solutions respectively measured without
and with the PVA species. The peak heights of the US profiles were I0 and IUS, which
were observed before and after US transduction at each PVA solution concentration.
Transmittance t=IUS/I0 (1) was calculated. Figure 3-4 shows that the US intensity
decreased at each frequency when the PVA concentration was 200 g/L. Results shows
that the viscous PVA solution of PVA217 exhibited a higher tendency to show
decreased transmittance at each frequency. To examine US absorption to the PVA
solution, we defined US absorption, AUS as
( )
( ⁄
)
(3.2)
Figure 3-5 shows the respective relation between PVA concentration (g/L) and A US for
a) PVA13, b) PVA31, c) PVA217 and d) PVA117. The absorptivity of the US to the
solution is expected to increase continuously with the PVA in higher concentration. It
was noteworthy that the experimental data showed a linear relation between PVA
concentration and AUS. Therefore, the absorptivity of the US can be expressed as
A=LC (3), where the value of L is the glass cell length (30 mm), and  in the equation
is the slope and constant, meaning that the area of the US absorptivity of the solution
medium having unit weight (L/g-cm). Therefore, we were able to convert the
68
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
absorptivity, US, given in units of centimeters and grams per liter to be that of unit of
L/g-cm = 0.1 m2/g. This constant meant that the value of US is the US absorption area
for unit weight PVA. Consequently, equation (3) was rewritten as AUS=0.1 USLC. As
indicated by Figure 3-5, the values of AUS increased continuously with the increased
PVA concentration, suggesting that the absorbed US increased continuously with
increased PVA concentration. In addition, the degree of the slope in the relation became
higher in the cases of the 43 kHz US. The resultant US is presented in Table 3-1. The
tendency of 43>96>23>141 kHz was noted for all PVA samples used in the resultant
US. Furthermore, the absorption of the US increased continuously with the molecular
weight of the PVA used. For example, at 43 kHz, the values of US were, respectively,
4.3×10-5, 5.3×10-5, 1×10-4, and 9×10-5 m2/g for PVA13, PVA31, PVA217, and PVA117.
The PVA217 presented higher absorptivity relative to other PVAs, indicating that
viscous PVA solution could adsorbed more sound. On other hand in comparison of
PVA217 and PVA117 having higher hydrolysis degree, the PVAs showed similar
tendency in the plots of AUS and PVA concentration that mean the hydrolysis change in
PVA217 and PVA117 had no influence on the US absorptivity
69
c P
Intensity [V]
00 g L
00 g L
6
4
b P
d P
3
0 s
0 s
00 g L
00 g L
N
00 g L
00 g L
N
Profiles intensity of the US waves before and after pass through the glass cell at 43 kHz, for a) PVA13 b) PVA31, c)
PVA217, and d) PVA117.
-8
-6
-6
-8
-4
-2
0
2
4
6
8
10
8
6
4
2
0
-2
-4
-6
-8
-10
-4
-2
0
2
N
0 s
0 s
00 g L
00 g L
N
8
10
8
6
4
2
0
-2
-4
-6
-8
-10
3
Figure 3-3
Intensity [V]
Intensity [V]
70
Intensity [V]
a P
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
Figure 3-4 Transmittance (t=IUS/I0) of each frequency US through 15 wt% of aqueous PVA.
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
71
Figure 3-5 US absorptivity (AUS=LC) of aqueous PVAs solutions with different concentrations. The US power dissipated was
adjusted in 8.5 – 9 W.
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
72
3.0×10-5
5.3×10-5
4.3×10-5
2.0×10-5
2.3×10-5
4.3×10-5
3.0×10-5
1.0×10-5
23 kHz
43 kHz
43 kHz
141 kHz
3.7×10-5
7.3×10-5
1.0×10-4
5.3×10-5
PVA217
4.7×10-5
6.7×10-5
9.0×10-5
5.3×10-5
PVA1117
The power dissipated of the US exposure was 8.5, 9, 8.7, and 8.8 W respectively, for 23, 43, 96, and 141 kHz
PVA31
PVA13
Frequency
Table 3-1 US coefficient (m2/g) for PVAs at different frequencies.
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
73
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
3.3.3 Change in FT-IR spectra observed at different times
In our previous work for PAA/Al2O3 aqueous slurry [9], the US exposure induced
change in the FT-IR spectra, especially in the OH stretching band region, which implied
that the US changed the chemical structure of the aqueous slurry. To elucidate the
change of the shear viscosity and their US absorption in aqueous PVA by US
exposure .FT-IR spectra of aqueous PVA before and after US exposure were measured
and compared. To analyze the water addition in the PVA, comparison of FT-IR spectra
of dry film and aqueous film of PVA was carried out. As described, the aqueous PVA
dropped in the CaF2 windows and then, the sandwiched windows was placed in the
water bath of the sonoreactor to be exposed to US.
After the US was stopped, FT-IR
measurements were conducted immediately. Figure 3-6 shows differences of FT-IR
spectra of the dried film and the aqueous PVA for a) PVA13, b) PVA31, c) PVA217
and d) PVA117. The FT-IR spectra showed that typical bands of PVA appeared at
3500–3200 cm-1 for the O–H stretching band. The non-hydrogen bonded or free
hydroxyl group is absorbed strongly in the 3700–3500 cm-1 region. Intermolecular
hydrogen bonding appeared at 3550–3200 cm-1. The stretching band observed at 3000–
2800 cm-1 shows stretching C–H from alkyl groups of the PVA [26]. The wavenumber
region between 1750–1680 cm-1 and 1150–1085 cm-1 showed stretching C=O and
non-saponificated –OCOCH3 group in the PVA. Moreover, the difference in the dry and
74
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
aqueous samples is clear in the 2600–3800 cm-1 region, which suggests that the water
molecules strongly hydrated with the OH groups of the PVA. Comparison of hydration
phenomenon of dry and aqueous PVA was made by peak deconvolution for PVA13,
PVA31, PVA217 and PVA117 as shown in Fig. 3-7, Fig. 3-8, Fig. 3-9 and Fig. 3-10,
respectively in the region of 3800–3000 cm-1. From FT-IR spectra of the dry and
aqueous films, we compared peak positions, determined from their second derivatives.
These spectra were decomposed into five Gaussian components by curve fitting [24, 25].
Five peaks were chosen to fit the OH stretching curve, due to it have been reported that
the PVA and water molecules might interact between 5 or 6 different ways [26-29].
The results are presented in Table 3-2. Here, peaks 1, 2, and 3 were respectively
assigned with OH groups of PVA bonded strongly with water molecules, OH groups of
PVA to bond with intermolecular crosslinks of PVA, and intramolecular interaction
with another neighbor OH group. In the other hand peaks 4 and 5 were assigned to
non-hydrogen bonded OH from PVA and free OH form water molecules, respectively.
The peak fitting data of the PVAs showed that the high-molecular-weight PVA, which
contained free OH, appeared in 3450–3400 cm-1 (peak 4). When a small amount of
water was added to the PVA systems, each FT-IR spectra became broader in the OH
stretching band region, especially in 3700–3000 cm-1. The water addition intensified the
75
b P
0
4000
0.05
0.1
0.15
0.2
0.25
0.3
3
0
4000
0.1
0.2
0.3
0.4
0.5
3
3500
3500
3000
3000
[cm -1 ]
wavenumber [cm -1]
2500
Wavenumber
2500
Film
No US
2000
Film
No US
2000
1500
1500
1000
1000
Figure 3-6 FT-IR spectra of a) PVA13, b) PVA31, c) PVA217, and d) PVA117. (Dot line is for dry PVA and solid line for aqueous
PVA with 25 wt% concentration.
Absorbance
76
Absorbance
a P
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
Absorbance
d P
Absorbance
c P
3500
3000
2500
0
4000
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0
4000
0.05
0.1
0.15
3500
3000
Wavenumber
2500
[cm-1]
Wavenumber[cm-1]
No US
Film
2000
2000
Film
0.25
0.2
No US
0.3
0.35
1500
1500
1000
1000
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
77
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
Figure 3-7 Comparison of FT-IR spectra of a) dry, and b) aqueous PVA13 in
wavenumber range of 3000-3800cm-1. The deconvoluted peaks were assigned by
showing Scheme 3-2.
Peak 1
Peak 2
Peak 3
Peak 4
Peak 5.
78
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
Figure 3-8 Comparison of FT-IR spectra of a) dry, and b) aqueous PVA31 in
wavenumber range of 3000-3800cm-1. The deconvoluted peaks were assigned by
showing Scheme 3-2.
Peak 1
Peak 2
Peak 3
Peak 4
Peak 5.
79
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
Figure 3-9 Comparison of FT-IR spectra of a) dry, and b) aqueous PVA217 in
wavenumber range of 3000-3800cm-1. The deconvoluted peaks were assigned by
showing Scheme 3-2.
Peak 1
Peak 2
Peak 3
Peak 4
Peak 5.
80
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
Figure 3-10 Comparison of FT-IR spectra of a) dry, and b) aqueous PVA117 in
wavenumber range of 3000-3800cm-1. The deconvoluted peaks were assigned by
showing Scheme 3-2.
Peak 1
Peak 2
Peak 3
Peak 4
Peak 5.
81
82
3411
3
5
4
3297
2
3418
3298
3219
Dry
Dry
3241
PVA
31
PVA
13
1
Peak
Index
3477
3409
3308
3241
Dry
PVA
217
3401
3310
3227
Dry
PVA
117
3613
3519
3421
3319
3222
aqueous
PVA
13
3616
3515
3420
3313
3227
aqueous
PVA
31
3638
3576
3418
3287
3154
aqueous
PVA
217
3648
3591
3438
3335
3135
aqueous
PVA
117
3631
3529
3394
3253
3633
3578
3448
3313
3227
5 min
5 min
3185
PVA
31
PVA
13
Table 3-2 Centered peak wavenumber determined by Curve-fitting for the OH stretching band.
3633
3559
3445
3346
3211
5 min
PVA
217
3639
3578
3454
3312
3141
5 min
PVA
117
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
spectral change in the 3500–3600 cm-1 region, probably because of water bonding with
the OH groups of PVA. The band of the 3600 cm-1 for peak 5 was assigned by the free
water band in the PVA with increasing molecular weight of PVA. Thereby, water
molecules hydrated with the OH group of PVA. Possible structural changes due to
thedrying process, it could be attributed to the decrement of free water, affect the
polymer-polymer distance, assisted in the formation of hydrogen bonds between OH
groups of the PVA and microcrystals [30-33] enhanced the peak at 1141 which is
related with the formation of microcrystals. As present in Figures 3-11, 3-12, 3-13, and
3-14 no significant changes at the band 1141 cm-1 and 1040 cm-1 were observed.
Therefore we concluded that the dry process had less effect the spectral properties of the
PVA film. As shown in Figs. 3-11, 3-12, 3-13, and 3-14, FT-IR spectra of the aqueous
PVA were measured after 43 kHz US exposure for 1, 3, and 5 min. The effect of the 43
kHz US was especially intense in the OH band. For 1000–1800 cm-1, but no change was
observed as a result of the US exposure. In extended wavenumbers of 3000–3800 cm-1
components were strengthened by US exposure, which implied that the US exposure
enhanced the peak 3 intensity assigned to intramolecular OH groups linked by hydrogen
bonds. Those bonds were broken, creating interaction with water molecules in the PVA
medium (Scheme 3-2). However, the PVA217 showed enhancement of peak 1 and peak
83
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
a
exposure
0.6
min of
0.5
3 min of
min of
Absorbance
0.4
0 min of
0.3
0.2
0.1
0
4000
3500
3000
2500
2000
1500
1000
Wavenumber [cm-1 ]
b
econvolution
0.6
0.5
3
Absorbance
0.4
0.3
0.2
0.1
0
3800
3700
3600
3500
3400
Wavenumber
3300
3200
3100
3000
[cm-1 ]
Figure 3-11 FT-IR spectra of PVA13 for the 43 kHz US exposure for a) 1, 3, and 5 min
and b) containing deconvoluted curve fitting in the after 5 min US exposure.
84
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
a
exposure
0.4
min of
0.35
3 min of
Absorbance
0.3
min of
0.25
0 min of
0.2
0.15
0.1
0.05
0
4000
3500
3000
2500
Wavenumber
b
2000
1500
1000
[cm -1 ]
econvolution
0.4
0.35
Absorbance
0.3
0.25
3
0.2
0.15
0.1
0.05
0
3800
3700
3600
3500
3400
Wavenumber
3300
3200
3100
3000
[cm -1 ]
Figure 3-12 FT-IR spectra of PVA31 for the 43 kHz US exposure for a) 1, 3 and 5 min
and b) containing deconvoluted curve fitting in the after 5 min US exposure.
85
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
a
exposure
Absorbance
0.5
0.45
min of
0.4
3 min of
0.35
min of
0.3
0 min of
0.25
0.2
0.15
0.1
0.05
0
4000
3500
3000
2500
Wavenumber
b
2000
1500
1000
[cm-1 ]
econvolution
0.45
0.4
0.35
Absorbance
0.3
0.25
3
0.2
0.15
0.1
0.05
0
3800
3700
3600
3500
3400
3300
3200
3100
3000
Wavenumber[cm -1 ]
Figure 3-13 FT-IR spectra of PVA217 for the 43 kHz US exposure for a) 1, 3 and 5
min and b) containing deconvoluted curve fitting in the after 5 min US exposure.
86
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
a
exposure
0.5
min of
3 min of
0.4
Absorbance
min of
0 min of
0.3
0.2
0.1
0
4000
3500
3000
2500
2000
1500
1000
wavenumber [cm -1 ]
econvolution
0.5
0.45
0.4
0.35
Absorbance
b
3
0.3
0.25
0.2
0.15
0.1
0.05
0
3800
3700
3600
3500
3400
Wavenumber
3300
3200
3100
3000
[cm -1 ]
Figure 3-14 FT-IR spectra of PVA117 for the 43 kHz US exposure for a) 1, 3 and 5
min and b) containing deconvoluted curve fitting in the after 5 min US exposure.
87
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
4 when exposed to 43 kHz US. Consequently, the US exposure induced redistribution of
the water hydration of the PVA segments. The interaction between water–PVA for the
and PVA–PVA for the peak 2 were strengthened by the US exposure. The change
suggests that the PVA crosslinkage of the OH groups was broken by the US exposure.
shown by b) deconvolution, in each spectrum was for 5 min exposure. In the figures, the
dashed lines show deconvolution results. In PVA13 and PVA31, the peak 3 peak 1 the
Subsequently, the water molecules bonded again to the OH groups. Scheme 3-2 shows
that US decreased the shear viscosity of the aqueous PVA arising from the breakage
ofhydrogen bonded network by the US exposure. This US effect suggests that the
increased intensity of the OH band in the 3500–3200 cm-1 region for the peaks 1 and 2
was attributable to the increased presence of water and PVA conditions. After the US
exposure, the changed FT-IR spectra reverted to the original spectra in each PVA
system. Figure 3-15 presents the value of the ratio of the FT-IR peak intensity of IOH at
3500–3200 cm-1and ICH at 2937 cm-1. After US exposure was stopped, the peak ratio
values for each PVA increased from 3.1 to 3.4, 4.1, 6.7, and 6 for PVA13, PVA31, PVA
217, and PVA117,respectively. This increase resulted from the OH-stretching band
enhancement attributable to the US exposure. Later, when the US exposure was stopped,
the values of IOH/ICH decreased gradually, finally returning to their original values
88
Scheme 3-2 Illustration of US effect on hydrogen bond network of PVA.
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
89
Figure 3-15 Time change in the ratio of IOH/ICH intensity observed in FT-IR spectra of a) PVA13 (♦),
(● .
c) PVA 217 (▲ , and d P
b) PVA 31 (■),
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
90
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
(IOH/ICH=3.1) within 30 min for PVA13, 55 min for the PVA31, 60 min for the PVA217,
and 70 min for the PVA117. These results were reasonable in consideration of the
recovery of the shear viscosity data after the US was stopped. Consequently, the
restructuring of hydrogen bonds made that the aqueous PVA solution was again viscous.
Results show that the US exposure broke the hydrogen bonds of PVA by US absorption
and also show the subsequent re-forming of the hydrogen bond in PVA solutions
without US.
3.4 Conclusion
Efficient change in the shear viscosity of the PVA aqueous solution was noted at 23, 43,
96, and 141 kHz for power dissipated of 8.5–9 W. Significant change was observed at43
kHz for the PVA systems. Application of US absorption demonstrated that US was
absorbed at high PVA concentrations and the absorptivity of US was estimated as
4.3×10-5, 5.3×10-5, 1.0×10-4, and 9.0×10-5 respectively, for PVA13, PVA31, PVA217,
and PVA117 at the 43 kHz US. Furthermore, the FT-IR spectra showed that the US
exposure affected OH-stretching groups of the PVA segment, which broke the hydrogen
bond crosslinks. Then, without US, the crosslinks were re-formed in the aqueous PVA.
91
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
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Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
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[14] J. R. Bae, J. K. Kim, M. H. Yi, Ultrasonic absorption and velocity measurements
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[16] C.A Finch, Chemistry and technology of water-soluble polymers. Plenum Press:
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[17] B. Briscoe, P. Luckham, S. Zhu, The effects of hydrogen bonding upon the
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[29] G. E. Walrafen, Raman Spectral Studies of the Effects of Temperature on Water
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95
Chapter 3 Ultrasound stimulus on aqueous polyvinyl alcohols
96
4 Chapter 4 Effect of Ultrasound on Changing Aqueous
Viscosity of Several Water Soluble Polymers
Abstract
The effect of ultrasound (US) on the shear viscosity of water-soluble polymers, poly
vinyl alcohol (PVA), polyethylene glycol (PEG), and poly acrylic acid (PAA), was
studied in aqueous solutions with US exposure of 23 kHz, 43 kHz, 96 kHz, and 141 kHz
for an 8.5-9 W US. The US exposure significantly decreased the shear viscosity of the
solutions in this order: 43 kHz > 23 kHz > 96 kHz > 141 kHz. When US exposure was
stopped, the shear viscosities of the aqueous polymer solutions reverted to their original
values. US stimulation during the decrease in viscosity was supported by the ultrasonic
power transmitted through the aqueous polymer solution. Additionally, FT-IR spectra
obtained during US exposure showed that hydrogen bonds in the aqueous polymer
solution could be broken, especially at 43 kHz. We concluded that US exposure
influenced hydrogen bonding interactions between the OH groups of the polymer and
water molecules in the aqueous medium. This finding was supported by US absorption
of the aqueous polymer solution in the transmittance model, which shows the US
absorptivity, US, for each polymer system.
97
Chapter 4 US effect on aqueous viscosity
4.1 Introduction
Ultrasound (US) has been widely applied in different fields, such as medicine,
engineering, and biology [1]. Due to the advantages of US, it is widely used in
sono-chemical processes [2, 3] as well as in food engineering and separation processes
[4, 5]. Smart materials responded when external stimuli, such as heat, light, or magnetic
fields, were applied [6]. However, few studies of US have demonstrated the ability of
external stimuli to change material properties. Recently, it was reported that US could
be used as a new type of trigger in the drug delivery of polymeric composite materials.
In these cases, a low US frequency was applied to encapsulate drugs, and the
hydrophilicity and high permeability of the materials improved the penetration of water
[7, 8]. In our previous works, copolymer microgels of N-isopropylacrylamide (NIPAM)
and acrylic acid (AA) using methylenebisacrylamide as a crosslinker demonstrated
US-responsive behavior in spherical polymer microgels [9, 10]. In addition, a
significant change in the shear viscosity was observed in Al2O3/polyacrylic acid (PAA)
slurry [11], and similar behavior was observed in NIPAM copolymers with PAA in
aqueous media [12] and carrageenans [13]. These variations were explained by the
breaking of polymeric hydrogen bonds in the microenvironment when US exposure was
performed in aqueous medium.
98
Chapter 4 US effect on aqueous viscosity
Regarding the changes in shear viscosity during US exposure, US absorption might
induce polymer changes, particularly those related to hydrogen bonded species in the
aqueous polymers used. It was reported that ultrasonic adsorption to polymeric medium
was evaluated by absorption coefficients, sound velocities and viscosity, for different
non-ionic and ionic polymer solutions, such as polyethylene glycol (PEG), polyvinyl
alcohol (PVA), and PAA at high frequencies of 2-130 MHz [14-18]. However, no
results for US using lower frequencies have been reported.
Nevertheless, water soluble polymers possessing different chemical structures for PEG,
PVA, and PAA are widely used in different industries. These polymers are generally
used as stabilizers for aqueous colloidal suspensions, and their properties in aqueous
media are strongly related to the viscosity of their aqueous media [19-24]. Therefore, if
the viscosity could be controlled by US, such a technology would possess quite an
effective advantage. However, the effect of US in polymer systems has not been well
characterized when lower US frequencies are used. The present study, therefore,
investigated the shear viscosity properties of the aqueous polymers of PVA, PEG, and
PAA as a function of ultra-sonication at various low frequencies: 23 kHz, 43 kHz, 96
kHz, and 141 kHz. Additionally, the effects of US in aqueous solutions were studied
using a US absorption model and were also observed using FT-IR spectroscopy in
99
Chapter 4 US effect on aqueous viscosity
aqueous solutions. It was concluded that absorption of US altered hydrogen bonding in
the aqueous solution.
4.2 Experimental
4.2.1 Materials and sample solution preparation
Water-soluble polymers, PEG, PVA, and PAA, were purchased from Sigma Aldrich
Co., St. Louis, MO, USA. The molecular weight of PEG was 100 000 Mw; the weight
of PVA was 146 000-186 000 Mw with a degree of hydrolysis of approximately
86-88 %, and the weight of PAA was 450 000 Mv. An aqueous solution with a 10 wt%
concentration for each polymer was prepared in distilled water and then purified using
an ion exchange column. The polymer solutions were heated for 2 hours to allow for
full dissolution at 60 ˚ . The transparent solutions obtained were slowly cooled at room
temperature and stored at that temperature for one day to allow for settling and to
eliminate air bubbles.
4.2.2 Shear viscosity measurements of the water-soluble polymers
A sonoreactor device (HSR-305; Honda Electronics Co. Ltd., Toyohashi, Aichi, Japan)
was used for the experiments (Scheme 4-1). The sonoreactor could be operated at four
frequencies: 23 kHz, 43 kHz, 96 kHz, and 141 kHz. A calorimetric study was also
100
Chapter 4 US effect on aqueous viscosity
Scheme 4-1 US experimental setting for the measurement of the shear viscosity in
polymer solution.
101
Chapter 4 US effect on aqueous viscosity
performed to calculate the US power dissipated in the water bath [25, 26]. The power
dissipated into the aqueous solution was between 8.5 and 9 W. The measurement setup,
as shown in Scheme 4-1 includes a Brookfield rotating viscometer (Tokyo Keiki Inc.,
Ohta-Ku, Tokyo, Japan) to measure the shear viscosity of the aqueous solutions. The
sonoreactor temperature was fixed at
˚
for all experiments by flowing water
through the sonoreactor. It was confirmed that no increase in temperature was detected
during the experiments. The shear viscosity was measured both prior to and after US
exposure. The viscosity was measured with a No. 2 rotor. The viscous solution was put
into a cylindrical glass vessel with a diameter of 40 mm and height of 120 mm and was
placed in the US sonoreactor. The sample solution was exposed to US for 5 min at each
frequency. The shear viscosity was measured at 1-min intervals.
4.2.3 Measurements of the US effect on the FT-IR spectra of the aqueous solutions.
FT-IR spectroscopy is a useful technique to examine the hydrogen bonding of
polymeric materials. Accordingly, the US effect on chemical changes in water-soluble
polymer solutions was analyzed via FT-IR spectroscopy, which was measured using an
FT-IR 4100 series spectrometer (Jasco Corp. Hachioji Tokyo, Japan). Aqueous polymer
solutions with a concentration of 10 wt% were lightly dropped onto a CaF2 window (30
mm diameter, 2 mm thickness; Pier Optics Co. Ltd. Tatebayashi, Gunma, Japan).
102
Chapter 4 US effect on aqueous viscosity
Another window was placed on top to cover the drop of solution, which formed a thin
layer between the plates. To prevent penetration of water into the sample window, when
being placed into the US water bath, the CaF2 windows were sealed with Parafilm. The
windows had no effect on polymer adsorption and no influence on the resulting FT-IR
spectra. All experiments were performed three times and were shown to have similar
results within an experiment. The FT-IR spectra were measured immediately using
absorbance mode following 1, 3, and 5 min of US exposure. For the FT-IR spectra,
spectral analysis of the OH and CH stretching bands was deconvoluted using a method
similar to that in our previous report, and these stretching bands ranged from 2400 to
3800 cm-1 for PAA and from 3000 to 3800 cm-1 for both PEG and PVA [13]. When the
centers of the fixed peaks of the original OH and CH stretching bands were determined
in the spectral data, their bands were decomposed into Gaussian components with peak
centers and the curve was then fitted using OriginPro 8.5.1.
4.3 Results and discussion
4.3.1 Effect of ultrasound on shear viscosity of water soluble polymers.
The shear viscosity of the aqueous polymer solutions was measured after US exposure
at 8.5-9 W for 5 min, after which time ultrasonication was stopped and the shear
viscosity was measured at 1 min intervals. Figure 4-1 shows the change in shear
viscosity as a function of time for each aqueous solution of a) PEG, b) PVA, and c)
103
Chapter 4 US effect on aqueous viscosity
PAA at pH 3; d) PAA at pH 5; and e) PAA at pH 10. Here, PAA solutions were
prepared at three pH values, 3, 5, and 10, because the extent of dissociation of the
-COOH group of PAA depends on the pH. The concentration of each polymer was fixed
at 10 wt% for the viscosity measurements. As observed previously, the shear viscosity
apparently decreased from the original values following US exposure in each case.
When the viscosity returned to its original value, each sample was exposed to US a
second time for 5 min. It was noted that the change in the shear viscosity during the
second cycle appeared similar to that during the first cycle. Therefore, these results
indicated that the US exposure could respond to the change in the shear viscosity. The
results also indicated that the change in the shear viscosity was caused by the US
stimulus, which was used as a trigger to induce a change in shear viscosity. Overall, the
43 kHz frequency was the most effective stimulus for the shear viscosity comparison to
the other frequencies. The decrease in the shear viscosity occurred in increasing order of
43 kHz > 23 kHz > 96 kHz > 141 kHz. It would be interesting to consider that the
comparison of the chemical structures of each polymer is made based on the viscosity
change due to US. For the 43 kHz sample, the PEG solution prior to US exposure was
543 cp and after US exposure changed to 474 cp. For the PVA solution, a change in
viscosity was observed from 1690 to 1260 cp, following US exposure. For PAA, a
104
Chapter 4 US effect on aqueous viscosity
change was observed from 785 to 725 cp at pH 3 and from 1740 to 1550 cp at pH 5.
When the shear viscosity was measured at pH 10 for the PAA solution, a value of 2320
cp indicated that no change occurred in the shear viscosity upon US exposure. The
polymer condition at pH 10 could be explained by the presence of electrostatic
repulsions between the COO- groups of PAA, thus leading to a higher viscosity than the
other samples at pH 3 and pH 5. Therefore, the PAA polymer chains were considered to
be more extended and to have fewer hydrogen bonds at pH 10.
4.3.2 Effect of US absorption on the aqueous polymer medium.
Because these changes in the shear viscosity due to US were observed in aqueous
solutions of polymers with different chemical structures, the US intensity was
monitored both before and after transmittance of the US through the sample solution to
analyze US absorption by the aqueous polymer solutions. Here, the transmittance of US
through the aqueous solution was investigated using a US detector to measure US
intensity. Thus, the US intensity was attenuated from I0 to IUS when the US passed
through the sample medium in a glass cell having L=30 mm containing 60 ml total
volume of the aqueous polymer solution at different polymer concentrations. The US
intensity decreased from I0 to IUS when the experiments were performed without and
then with polymer in solution. The peak heights of the US profiles were measured by
105
Chapter 4 US effect on aqueous viscosity
ycle
ycle
550
550
535
535
520
141 kHz
505
96 kHz
23 kHz
43 kHz
490
Shear Viscosity [Cp]
Shear Viscosity [Cp]
a P
520
141 kHz
505
96 kHz
23 kHz
43 kHz
490
exposure
475
exposure
475
460
460
0
5
10
15
20
25
0
5
10
Time [min]
ycle
20
25
ycle
171 0
171 0
165 0
165 0
159 0
159 0
153 0
141 kHz
147 0
96 kHz
23 kHz
141 0
43 kHz
Shear Viscosity [Cp]
Shear Viscosity [Cp]
b P
15
Time [min]
135 0
153 0
141 kHz
147 0
96 kHz
23 kHz
141 0
43 kHz
135 0
129 0
129 0
exposure
exposure
123 0
123 0
0
5
10
15
20
25
30
35
40
Time [min]
0
5
10
15
20
25
30
35
40
Time [min]
Figure 4-1Change of shear viscosity for the aqueous a) PEO, b) PVA, c) PAA pH 3, d)
PAA pH 5, and e) PAA pH 10 with 10 wt% concentration. The US power dissipated
was 8.5-9.
106
Chapter 4 US effect on aqueous viscosity
at pH 3
ycle
ycle
790
790
780
780
770
760
141 kHz
96 kHz
750
23 kHz
43 kHz
740
Shear Viscosity [Cp]
Shear Viscosity [Cp]
c P
730
770
760
141 kHz
96 kHz
750
23 kHz
43 kHz
740
730
exposure
720
exposure
720
0
5
10
15
20
25
30
0
5
Time [min]
at pH
ycle
175 0
172 5
172 5
170 0
170 0
167 5
165 0
141 kHz
162 5
96 kHz
23 kHz
160 0
43 kHz
25
30
167 5
165 0
141 kHz
162 5
96 kHz
23 kHz
160 0
43 kHz
157 5
155 0
155 0
exposure
exposure
152 5
152 5
0
5
10
15
20
25
30
0
5
Time [min]
at pH 0
10
15
20
25
30
Time [min]
ycle
ycle
250 0
200 0
150 0
141 khz
100 0
96 kHz
23 kHz
exposure
500
43 kHz
0
Shear Viscosiry [Cp]
250 0
Shear Viscosiry [Cp]
20
ycle
175 0
157 5
e P
15
Time [min]
Shear Viscosity [Cp]
Shear Viscosity [Cp]
d P
10
200 0
150 0
141 khz
100 0
96 kHz
500
23 kHz
exposure
43 kHz
0
0
5
10
15
20
Time [min]
25
30
0
5
10
15
20
25
30
Time [min]
107
Chapter 4 US effect on aqueous viscosity
oscilloscope after the US intensity was received by the probe. Then, I0 and IUS were
observed both before and after US transduction at each aqueous polymer solution
concentration. The transmittance t=IUS/I0 (1) was calculated for different polymer
solutions. Results show that the polymer solution exhibited a tendency to show that I0 >
IUS, meaning that the US transmittance decreased at each frequency as a function of US
absorption. To examine the degree of US absorbed by the aqueous polymer solution, we
defined US absorption as AUS,
( )
( ⁄
) .
(4.2)
The absorptivity of the US in the solution is expected to increase continuously with
increasing polymer concentration. Notably, the experimental data showed a linear
correlation in each polymer system. Therefore, the absorptivity of the US can be
expressed as AUS=USLC, where L is the glass cell length (30 mm) and US is the
constant slope. The value US represents the area of US absorptivity in the solution
medium per unit weight at the transduced distance (L/g-cm). Therefore, we were able to
perform the following conversion of the absorptivity, US, given in units of centimeters
and grams per liter: L/g-cm = 0.1 m2/g. This unit constant indicates that the value of US
is the US absorption area for the unit weight of each polymer solution.
108
Chapter 4 US effect on aqueous viscosity
In Figure 4-2 the slope in the equation increased at a US of 43 kHz for PEG, PVA and
PAA at pH3. The resultant US is listed in Table 4-1.The trend increased in order of 43
kHz > 23 kHz > 96 kHz > 141 kHz for PEG, PVA, and PAA at pH 3. For example, at
43 kHz, the values of US were 7.6×10-5, 6.3×10-5, and 5.3×10-5 m2/g for PVA, PAA at
pH 3, and PEG, respectively. The value for PVA represented a higher absorptivity
relative to the others, indicating that PVA solutions could adsorb more US. However,
the PAA samples at pH 5 and pH 10 possessed different US absorptivities, even though
the same polymer solution was used at different pHs. Relative to the viscosity at pH 3, a
high value for viscosity was observed at pH 10. This outcome was due to the extension
of PAA chains because of the electrostatic effects of charged PAA. However, Figure
4-2 showed that the results for US were very low at pH 10 for the PAA solution. This
result seemed to suggest very low absorption of US in such a viscous solution as that of
charged PAA. Therefore, very little US absorption occurred in the dissociated PAA
without OH groups, although high viscosity was observed in the aqueous PAA solution
at pH 10.
4.3.3 Effect of ultrasound on change in FT-IR spectra of water soluble polymers.
To clarify the change in the shear viscosity and the level of US absorption in each
aqueous polymer solution both before and after US exposure, FT-IR spectra were
109
Chapter 4 US effect on aqueous viscosity
a P
0.3
43 kHz
Absortivity [AUS]
23 kHz
0.2
96 kHz
141 kHz
0.1
0
0
30
60
90
120
150
120
150
Concentration [g/L]
b P
43 kHz
Absortivity [AUS]
0.3
23 kHz
96 kHz
0.2
141 kHz
0.1
0
0
30
60
90
Concentration [g/L]
Figure 4-2 US absorptivity (AUS=LC) of aqueous polymer solutions with different
concentr ations. The US power was adjusted in 8.5 –9 W.
110
Chapter 4 US effect on aqueous viscosity
c P
at pH 3
0.3
Absortivity [AUS]
43 kHz
23 kHz
0.2
96 kHz
141 kHz
0.1
0
0
d P
30
60
90
120
150
120
150
Concentration [g/L]
at pH
0.3
Absortivity [AUS]
43 kHz
23 kHz
0.2
96 kHz
141 kHz
0.1
0
0
30
60
90
Concentration [g/L]
e P
at pH 0
0.15
Absortivity [AUS]
43 kHz
23 kHz
0.1
96 kHz
141 kHz
0.05
0
0
30
60
90
120
150
Concentration [g/L]
111
112
PVA
7.6×10-5
5.0×10-5
3.3×10-5
3.0×10-6
PEO
5.3×10-5
3.3×10-5
2.3×10-5
3.3×10-6
Frequency
43 kHz
23 kHz
96 kHz
141 kHz
3.0×10-6
3.0×10-5
4.3×10-5
6.3×10-5
PAA pH 3
Table 4-1 US coefficient (m2/g) for aqueous polymer solution at different frequencies.
3.0×10-6
2.3×10-5
2.6×10-5
3.0×10-5
PAA pH 5
3.3×10-7
3.0×10-6
3.0×10-6
3.0×10-6
PAA pH 10
Chapter 4 US effect on aqueous viscosity
Chapter 4 US effect on aqueous viscosity
obtained for the aqueous polymer solutions. The experimental method was similar to
previous reports for water soluble polysaccharides [13] and water-swelled hydrophilic
microgels [10]. In the present experiments, for PEG, PVA, and PAA, a small amount of
polymer solution was dropped onto the CaF2 windows, and the sandwiched windows
were then placed into the water bath of the sonoreactor to be exposed to US. FT-IR
measurements were performed immediately after US exposure was terminated. It was
confirmed that chemical adsorption of polymer to the CaF2 windows did not occur after
the FT-IR measurements were finished. This phenomenon was checked by washing the
windows after US exposure. Figure 4-3 shows the FT-IR spectra of the aqueous
polymers for a) PEG, b) PVA, c) PAA at pH 3, d) PAA at pH 5, and e) PAA at pH 10
both before and after various US exposures were performed for 1, 3, and 5 min. The
FT-IR spectra exhibited the characteristic bands for PEG and PVA at 3000-3800 cm-1
[27-29]. FT-IR peaks for PEG [27, 28] and PVA [29] in water were assigned at
3300-3500 cm-1 for OH stretching of the polymers and water molecules. For PAA, the
OH stretching band was noted at 2500-3800 cm-1 [30]. For the monomeric acid OH at
3500-3800 cm-1 and the hydrogen bonded acid OH at 2500-3500 cm-1, a characteristic
band for each polymer was observed in these regions [31]. A non-hydrogen bonded
peak for the polymer chain and water molecules appeared in the 3400-3800 cm-1 region,
113
Chapter 4 US effect on aqueous viscosity
a P
0.7
min of
0.6
3 min of
min of
Absorbance
0.5
0 min of
0.4
0.3
0.2
0.1
0
4000
3500
3000
2500
Wavenumber
2000
1500
1000
1500
1000
[cm-1]
b P
0.5
min of
3 min of
0.4
Absorbance
min of
0 min of
0.3
0.2
0.1
0
4000
3500
3000
2500
2000
Wavenumber [cm-1]
Figure 4-3 FT-IR spectra before and after US exposure at different times of a) PEO, b)
PVA, c) PAA pH 3, d) PAA pH 5, and e) PAA pH 10 with 10 wt% concentration
114
Chapter 4 US effect on aqueous viscosity
c P
at pH 3
0.6
min of
Absorbance
0.5
3 min of
0.4
min of
0.3
0 min of
0.2
0.1
0
4000
3500
3000
2500
2000
1500
1000
1500
1000
1500
1000
Wavenumber [cm-1]
d P
at pH
0.35
min of
Absorbance
0.3
3 min of
0.25
min of
0.2
0 min of
0.15
0.1
0.05
0
4000
3500
3000
2500
Wavenumber
e P
at pH 0
0.5
min of
3 min of
0.4
Absorbance
2000
[cm-1]
min of
0.3
0 min of
0.2
0.1
0
4000
3500
3000
2500
2000
Wavenumber [cm-1]
115
Chapter 4 US effect on aqueous viscosity
and strong interactions between the polymer chain and water were observed in the
3000-3400 cm-1 region due to hydrogen bonding. In the 2500-2600 cm-1 region, Jean et
al. reported that the carboxylic acid groups are hydrogen bonded to water [32], which is
indicated by ‗X‘ in the spectra in Figure 4-3(c) and (d). Furthermore, carboxylic dimers
display an OH stretching band in the region of 2500-3300 cm-1, which is generally
centered near 3000 cm-1 [33]. Similar results for inter- and intra-hydrogen bonded bands
for PAA were reported [31-34]. In addition, a band observed at 2800-3000 cm-1 was
attributed to CH stretching from alkyl groups [28, 31]. The wavenumber region between
1500 cm-1 and 1800 cm-1 corresponded to a C=O group, and the peak at 1640 cm-1
corresponded to OH bending. In PAA at pH 3, the carbonyl band was centered at 1710
cm-1. When PAA was tested at pH 5, there were two peaks centered at 1710 cm-1 and
1540 cm-1 for the carbonyl bands [35, 36]. This result indicated that the carboxylic acid
group was partially dissociated: -COOH  -COO- + H+. For PAA at pH 10, it was
interesting to note that the OH band shifted toward a lower wavenumber region of
3200-3400 cm-1 (Figure 4-4). Nevertheless, the spectral change caused by US exposure
was less than that of the PAA solution at pH 3. For PAA solutions at pH 3 and 5, dimer
formation of –COOH groups was observed in the 2400-2700 cm-1 region (Figure 4-5).
However, for PAA at pH 10, no dimer formation was indicated, thereby indicating
116
Chapter 4 US effect on aqueous viscosity
dissociation of -COOH  -COO- + H+. Additionally in Figure 4-5 the OH stretching
band changed for a) PEG, b) PVA, and c) PAA at pH 3. For further analysis, the FT-IR
spectra of these aqueous polymers were deconvoluted in the 2400-3800 cm-1 region to
compare their peak positions.
For PEG and PVA, OH and CH bands were found in the resulting FT-IR spectra.
Therefore, these spectra were deconvoluted to consider both stretching bands in the
wavenumber region. The spectra were decomposed into Gaussian components by curve
fitting [13, 27]. The peak center results are summarized in Table 4-2. Figue 4-4 displays
the fixed curve of the OH stretching of aqueous polymer without US exposure for a)
PEG, b) PVA and c) PAA at pH 3. In addition, the fixed curve of CH stretching was
included in the spectra. For the deconvoluted spectra, peak 1 was assigned to the CH
stretching bands [28, 31]. Peak 2 was assigned to the strong hydrogen bond interactions
between water and the OH groups from the polymer chain [27]. Here, for PEG and PVA,
peaks 3 and 4 were assigned to the strong hydrogen bond interactions between the
polymer and water molecules and to the weak hydrogen bond interactions between the
polymer and water molecules, respectively [28, 29]. Peaks 5 and 6 were assigned to free
OH groups from either the polymer or water molecules and to those from free water
molecules, respectively [29, 30, 40].
117
Chapter 4 US effect on aqueous viscosity
a P
0.4
3
Absorbance
0.3
0.2
6
0.1
0
3800
3600
3400
3200
3000
2800
2600
2400
2800
2600
2400
Wavenumber [cm-1]
b P
0.4
Absorbance
0.3
3
0.2
0.1
6
0
3800
3600
3400
3200
3000
Wavenumber [cm-1]
Figure 4-4 Comparison of deconvoluted OH stretching band of a) PEO, b) PVA, c)
PAA pH 3, d) PAA pH 5, and e) PAA pH 10 without US exposure
118
Chapter 4 US effect on aqueous viscosity
c P
at pH 3
Absorbance
0.4
0.3
0.2
6
0.1
3
X
0
3800
3600
3400
3200
3000
Wavenumber
d P
2800
2600
2400
[cm-1]
at pH
Absorbance
0.3
0.2
6
0.1
3
X
0
3800
3600
3400
3200
3000
Wavenumber
e P
2800
2600
2400
2800
2600
2400
[cm-1]
at pH 0
Absorbance
0.4
0.3
6
0.2
0.1
3
0
3800
3600
3400
3200
3000
Wavenumber [cm-1]
119
Chapter 4 US effect on aqueous viscosity
a P
0.7
0.6
3
Absorbance
0.5
0.4
0.3
0.2
6
0.1
0
3800
3600
3400
3200
3000
Wavenumber
2800
2600
2400
2800
2600
2400
[cm-1]
b P
0.5
Absorbance
0.4
3
0.3
6
0.2
0.1
0
3800
3600
3400
3200
3000
Wavenumber
[cm-1]
Figure 4-5 Comparison of deconvoluted OH stretching band of a) PEO, b) PVA c)
PAA pH 3, d) PAA pH 5, e) PAA pH 10 after 5 minutes of US exposure.
120
Chapter 4 US effect on aqueous viscosity
c P
at pH 3
0.6
Absorbance
0.5
0.4
0.3
6
3
0.2
0.1
X
0
3800
3600
3400
3200
3000
2800
2600
2400
Wavenumber [cm-1]
d P
at pH
0.35
Absorbance
0.3
0.25
0.2
6
0.15
0.1
3
0.05
X
0
3800
3600
3400
3200
3000
2800
2600
2400
2600
2400
Wavenumber [cm-1]
e P
at pH 0
0.5
Absorbance
0.4
6
0.3
0.2
0.1
0
3800
3
3600
3400
3200
3000
Wavenumber
2800
[cm-1]
121
122
3613
3623
3608
3499
3615
3617
3522
6
3537
3534
3395
5
3384
3473
3430
3415
3249
4
3248
3338
3221
3092
Y
3242
3075
3243
3061
3
3068
3071
2
0 min
2927
2949
5 min
2921
2948
0 min
1
2919
5 min
3612
3453
3338
3249
3092
2927
2555
5 min
PAA at pH 3
2548
0 min
PVA
X
Peak
US
PEG
3633
3497
3390
3228
3048
2939
2546
0 min
3639
3473
3387
3239
3054
2939
2546
5 min
PAA at pH 5
Table 4-2 Centered peak wavenumber determined by Curve-fitting for the OH stretching band.
3630
3484
3365
3226
3080
2941
0 min
3591
3461
3368
3223
3080
2939
5 min
PAA at pH 10
Chapter 4 US effect on aqueous viscosity
Chapter 4 US effect on aqueous viscosity
For PAA, peaks 2 and X corresponded to the PAA dimer interactions, and an additional
overtone of approximately 2650 cm-1 and 2550 cm-1 [35] indicated the presence of
strong hydrogen bond interactions between -COOH groups. Peak Y was assigned to
weak hydrogen bond interactions [32, 36, 41]. Figure 4-5also contains the fixed curves
of a) PEG, b) PVA, c) PAA at pH 3, d) PAA at pH 5 and e) PAA at pH 10 for data
regarding US exposure. Comparison of a) PEG with Fig. 4 a) and Fig. 5 a) showed that
peak 1 for the CH band and peak 2 for the hydrogen bonding of water-OH group
underwent less change. However, the intensity of peak 5 decreased, whereas peak 4
became intense, after US exposure. The change in Figure 4-5 a) meant that free OH
groups of PEG could bind with water at the end of the polymer chain. For PVA having
side OH groups, it was similarly observed that the intensity of peak 5 decreased, while
peak 6 increased as a result of US exposure. This result could explain the US-enhanced
breakage of the interactions between water molecules and the OH groups of PVA.
In the case of c) PAA at pH 3, the band intensities of peaks 4 and 6 were intense
following US exposure. However, hydrogen bonds due to the –COOH group in the
dimer at approximately 3000-3200 cm-1 were significantly changed. This result
indicated that US was effective in breaking the –COOH dimers and increased the
population of free OH groups from –COOH or water molecules. At pH 5 and pH 10, the
123
Chapter 4 US effect on aqueous viscosity
population of each peak changed less before and after US exposure. The insignificant
change at pH 10 could be due to the full dissociation of carboxylic acid groups:
COOHCOO-+H+. Furthermore, the 1700 cm-1 band for C=O stretching contains
useful information about the hydrogen bonded and non-hydrogen bonded carboxyl
groups of PAA [36]. Therefore, analysis similar to that of the C=O band was performed
with the OH band in Figs 4 and 5. Figure 4-6 shows the FT-IR spectra observed near the
1700 cm-1 region. In the C=O stretching region, the curve fitting spectra of the linear
oligomer, cyclic dimer, side-on dimer and monomeric side chain carboxylic groups
were obtained for PAA at 1676 cm-1, 1692 cm-1, 1710 cm-1, and 1730 cm-1, respectively.
The peaks at 1648 cm-1 and 1622 cm-1 were assigned to water molecules interacting
with PAA [38, 39], and the peak at 1562 cm-1 corresponded to dissociation of
carboxylic acid groups [41]. Table 4-3 also lists each band in the FT-IR spectra both
without and with US exposure in the range of 1500-1800 cm-1. By increasing the US
exposure time from 1 to 5 min, the intensity of the 1690 cm-1 band increased. This result
indicated that water molecules could associate with the C=O group in PAA at pH 3
following US exposure. A similar tendency was observed in the spectrum at pH 5 for
partially dissociation of COO- in PAA as shown in Figure 4-3(b). A similar result was
also observed in PVA at 1675 cm-1 for the –O-C=O group, which remained intact
124
Chapter 4 US effect on aqueous viscosity
without hydrolysis of the acyl acetate group. Altogether, these data indicated that US
exposure enhanced water solvation to the –C=O group in the polymer (Scheme 4-2).
Figure 4-7 shows the change in the ratio of the IOH/ICH intensity as a function of time in
the FT-IR spectra for a) PEG; b) PVA; and c) PAA at pH 3, d) pH 5 and e) pH 10. After
US exposure ceased, the values of the peak ratios in the FT-IR spectra obtained at pH 3
and pH 5 increased. This outcome resulted from the attribution of the OH group to the
free COOH group or water molecule, as the during US exposure. Notably, the values of
IOH/ICH decreased gradually and returned to their original values within 60 min, when
US exposure ceased. However, no change occurred at pH 10, even though US exposure
occurred. Consequently, the hydrogen bonds were re-formed, and the aqueous polymer
solution became viscous again, as shown in Figure 4-1 It was reasonable to conclude
that US exposure disrupted the hydrogen bonds of the aqueous polymer solutions of
PEG, PVA and PAA at pH 3 and pH 5 due to US absorption and could enhance water
solvation into the polymer.
As mentioned, the present paper could provide the first results of the effect of US on
different chemical structures of water-soluble polymers, which exhibited similar
amounts of US absorption to form free OH groups in water following US exposure, as
shown in Scheme 4-2.
125
Chapter 4 US effect on aqueous viscosity
a P
without
0.2
Absorbance
0.15
e
0.1
d
c
f
b
0.05
a
0
1800
1750
1700
1650
Wavenumber
b P
1600
1550
1500
1550
1500
[cm-1]
for min
Absorbance
0.2
e
0.15
d
b
0.1
c
0.05
a
f
0
1800
1750
1700
1650
Wavenumber
1600
[cm-1]
Figure 4-6 Comparison of the deconvoluted C=O stretching bands of PVA, PAA at
pH 3 and PAA at pH 5 prior to and following 5 min of US treatment.
126
Chapter 4 US effect on aqueous viscosity
c P
at pH 3 without
0.4
Absorbance
0.3
f
0.2
d
b
g
0.1
c
a
e
0
1800
1750
1700
1650
1600
1550
1500
Wavenumber [cm-1]
d P
at pH 3 for min
0.4
Absorbance
0.3
f
0.2
g
b
d
0.1
e
c
a
0
1800
1750
1700
1650
Wavenumber
1600
1550
1500
[cm-1]
127
Chapter 4 US effect on aqueous viscosity
e P
at pH without
0.2
Absorbance
0.15
f
a
0.1
c
0.05
b
e
g
d
0
1800
1750
1700
1650
Wavenumber
f P
1600
1550
1500
[cm-1]
at pH for min
0.2
Absorbance
0.15
a
c
0.1
g
0.05
e
f
b
d
0
1800
1750
1700
1650
Wavenumber
128
1600
[cm-1]
1550
1500
1738
1731
1739
g
1672
1712
1714
1676
1642
1712
1675
d
1648
1623
f
1648
c
1623
1552
0 min
1694
1622
b
1561
5 min
e
1562
0 min
a
Peak
US
PVA
PAA pH 3
1728
1710
1692
1671
1643
1626
1552
5 min
Table 4-3 Centered peak wavenumber determined by curve fitting for the C=O stretching band.
1730
1710
1691
1676
1646
1623
1553
0 min
PAA pH 5
1728
1710
1696
1647
1626
1552
5 min
Chapter 4 US effect on aqueous viscosity
129
Chapter 4 US effect on aqueous viscosity
Figure 4-7 Time change in the ratio of IOH/ICH intensity observed in FT-IR spectra of a)
PEO (♦), b) PVA (▲), c) PAA pH 3 (■), d) P
pH (● and e P
pH 0 ().
130
Chapter 4 US effect on aqueous viscosity
Scheme 4-2 Hydrogen bond crosslinked structures of a) PEG, b) PVA, and c) PAA with
water.
131
Chapter 4 US effect on aqueous viscosity
4.4 Conclusion
The present paper concluded that US, especially at 43 kHz, induced a change in the
shear viscosity due to the disruption of hydrogen bonds by efficient US absorption by
the aqueous medium and to the formation of free water with OH groups and of OH
groups in the water-soluble polymers. We also evaluated the values of US absorptivity
for US, which were 5.3×10-5, 7.6×10-5, 6.3×10-5, 3.0×10-5, and 3.0×10-6, for PEG; PVA;
and PAA at pH 3, pH 5, and pH 10, respectively, at a frequency of 43 kHz. US exposure
disrupted the hydrogen bonds in the polymers, especially at the OH groups, and also
enhanced the solvation of water to each OH and C=O group.
Reference
[1] T. J. Mason, J.P. Lorimer, Applied sonochemistry: The uses of power ultrasound
in chemistry and processing. (Wiley-VCH Verlag GmbH, Weinheim, 2002.)
[2] G. J. Price, Current trends in sonochemistry; Cambridge, Royal society of
sonochemistry, (Thomas Graham House, Science Park, Cambridge, 1992.)
[3] R. Eldik, C.D. Hubbard, Chemistry under extreme or non-classical conditions,
(Wiley& Sons: New York, 1996.)
[4] T. J. Mason, L. Paniwnyls, J. P. Lorimer, The uses of ultrasound in food
technology, Ultrason. Sonochem., 3 (1996) s253-s260.
[5] F. Chermat, N. Hoarau, Hazard analysis and critical control point (HACCP) for an
ultrasound food processing operation, Ultrason Sonochem., 11 (2004) 257-260.
132
Chapter 4 US effect on aqueous viscosity
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137
Chapter 4 US effect on aqueous viscosity
138
5 Chapter 5 Sono-respond on Thermosensitive Polymer
Microgels Based on Cross-linked
Poly(N-isopropylacrylamide-co-acrylic acid)
Abstract
Ultrasound (US) exposure strongly influenced thermosensitivity of microgels attracted
with both N-isopropylacrylamide (NIPAM) and acrylic acid (AA) segments, due to that
hydrogen bonds of carboxylic acid segments in microgels were broken by US and then
the hydration with water occurred. US induced critical effects on the volume phase
transition temperature of the swelled NIPAM gel (PNAM). It was observed after the US
exposure that the particle size was increased and the phase transition of the microgels
shifted toward larger temperature regions of the hydrodynamic diameter. FT-IR
spectroscopic data of the swelled microgel showed that the free OH stretching band
intensity of the COOH segments was enhanced by the exposure, but the band intensity
returned to its original level without the US exposure. This meant that the US stimulus
broke hydrogen bonding of the microgel and induced hydration of water in the hydrogel
environment. Finally, regeneration of the hydrogen bonds in the microgel was occurred
after the US exposure.
139
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
5.1 Introduction
Environmentally sensitive polymers have attracted much attention in recent years as
smart polymers. Generally, the external stimuli that these materials respond can be
classified as temperature, light, pH, and mechanical force.
[1-7]
Stimuli-responsive
polymers are one of the most attractive among varieties of responsive materials.
Controlling their polymeric behavior offers technical interest for various applications in
the fields of engineering and biotechnology
[8-12]
. The photochromic polymers and the
electro-active polymers are representative examples of functional materials that have
attractive attention by researchers and engineers in the recent years. In the case of
temperature, it is well known that Poly(N-isopropylacrylamide) (PNIPAM) and related
copolymers are studied for their thermo-sensitive properties. There are many reports on
modifying the volume phase transition temperature (VPTT) of microgels by
incorporation of functional monomers
[13-17]
. For example, Kawaguchi et al. reported
that PNIPAM promoted the adsorption of proteins, when the thermosensitive surface of
microgel became to be hydrophobic above the lower critical solution temperature
(LCST)
[18]
. They found that such hydrogel allowed the release of hydrophilicity and
hydrophobicity behavior by changing temperature. Also, US was used in preparation of
poly(N-isopropylacrylamide-co-acrylic acid) P(NIPAM/AA) gels because of the
140
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
mass-transfer acceleration and cavitation effects caused by US [19], but no attention was
paid as external stimuli.
While there have been many examples of sensitive polymeric materials to respond to
such external stimulus, sound like ultrasound has reported very little. In 2006, we
reported that US stimulated the thermosensitivity of PNIPAM hydrogels having
carboxylic acid groups [20]. More recently, US stimulus effect on hydrogen bonding in
networked alumina and polyacrylic acid slurry demonstrated that US waves emitted
with three different frequencies of 28, 45, and 100 kHz showed stimulus effect on
viscosity change
[21]
. This was because of breakage of the hydrogen bonding networks
of alumina and PAA in the slurry solution. On the other hand, in previous report, the
thermosensitivity of NIPAM gels controlling their swelling/shrinking behavior was
examined. Although this report was the first example of using US as stimulus [20], it was
still wondered that the volume phase transition of the NIPAM gels responded to the
sound stimulation. Therefore, we have focused in the use of US as new stimulus for
the reversible deformation of polymers. In the present article, it would be emphasized
that US could be an efficient candidate as external stimuli for the microgel swelling. We
focused on the US influenced to the swelling/shrinking behavior of microgel of
poly(N-isopropylacrylamide-co-acrylic
acid)
(PNAM), which was terpolymerized
141
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
using N-isopropylacrylamide, acrylic acid,
and N,N’-methylenbisacrylamide by
surfactant free polymerization in water. The change in the volume phase transition of
high cross-linked PNAM microgel (Scheme 5-1) was examined after the US was
exposed. For the microgels, it was found that the swelling/shrinking behavior was
significantly different in the PNAM microgels having hydrophobic attraction of the
NIPAM segment and the hydrogen-bonding interaction between NIPAM and AA
segments
[9]
. In addition, PNAM microgel exposed with US showed thermo-responsive
swelling gelation behavior with a large hysteresis over a wide range of temperatures
around its phase-transition temperature. vidence was presented that the
influenced
the swelling/shrinking behavior of microgel as a function of temperature.
5.2 Experimental
All chemicals were obtained from Nakarai Tesque (Tokyo, Japan) unless otherwise
noted. N-isopropylacrylamide (NIPAM) and N,N’-methylenebisacrylamide (MBAA)
were purified by recrystallization from hexane and methanol, respectively. Potassium
persulfate (KPS) and acrylic acid (AA) were used as received without further
purification.
experiments.
142
eionized water with a resistivity of
8.
MΩ-cm was used in all
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
a)
b)
Scheme 5-1 Chemical structures of (a) PNAM and (b) PNM.
143
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
The microgels containing NIPAM, AA and MBAA cross-linker (Scheme 5-1) were
synthesized using surfactant-free emulsion polymerization procedure
[12]
. Here, the
microgel with acrylic acid group was named with PNAM. In order to prepare the
PNAM microgels, 17.7 mmol NIPAM, 4.3 mmol AA, and 2 mmol MBAA were
dissolved in 350 ml deionized water in a 500 ml round-bottomed flask equipped with a
condenser, a nitrogen inlet, a stirrer, and a thermometer. Nitrogen was bubbled into the
solution, and the polymerization system was kept at 70 ºC. After equilibrium, 0.26 g of
KP was dissolved in 0 ml deionized water and added into the flask to initiate the
polymerization. The reaction was continued for 6 h under 200 rpm stirring. After
polymerization, all of the prepared microgels were centrifuged at 13,000 rpm for 20 min
to separate them from the medium. Then, the precipitated microgel polymers were
re-dispersed in deionized water for 24 h. This purification procedure was repeated three
times to eliminate the unreacted monomers and free electrolytes. Also, crosslinked
PNM microgel without AA was prepared with same procedure from 22 mmol NIPAM
and 2 mmol MBAA.
The US device used in the experiment was an ultrasonic cleaner (Ultrasonic Multi
Cleaner W115; Honda Electronics Co., Ltd., Toyohashi, Japan). A stainless steel water
bath (30x30x30 cm3) was equipped with seven attached transducers with 3 cm diameter
144
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
in the side walls of the ultrasonic water bath, which were connected to the side wall of
the water bath. We confirmed that slight temperature elevation was observed in US
exposure. Therefore, the water bath temperature was maintained at 20 °C as described
in previous reports
[21]
. The US intensity in the ultrasonic water bath was estimated
using an immersion transducer probe (V301; Panametrics Japan Co., Ltd., Tokyo, Japan)
that was connected to a pulse receiver (Model 5058PR; Olympus Corporation, Tokyo,
Japan). The received US intensity was displayed as a function of time in an oscilloscope
and was adjusted to be same in each frequency. The relation between frequency and the
amplitude height was measured as previously reported.
[21]
The US frequencies used for
experiments were 28, 45, and 83 kHz with input power of 200 W, equivalents to output
power of 50 W which was determined by calorimetric method [22].
Before US exposure, each microgel was well dispersed for over 1 day in water at pH 5.
The solution pH was adjusted with dilute aqueous HCl and NaOH solutions. Then, this
microgel solution was provided to the US exposure with each frequency and exposure
time.
After the US was exposed, the phase transition behavior of microgel particles was
measured by using Laser diffraction particle distribution instrument (Wing-SALD-7000;
Shimadzu Corporation, Kyoto, Japan) with 405 nm laser beam. Sample aqueous
145
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
solution was put in quartz cell (180x40x10 mm3) equipped with Electronic digital
thermostat (Thermo eye U; Saginomiya Co., Ltd., Tokyo, Japan). The temperature was
continuously raised from 1 ºC per min and the hydrodynamic diameter was recorded at
each temperature by using the electronic digital thermostat.
The
FT-IR
spectra
of
the
microgels
were
measured
by a
FT-IR-8400s
spectrophotometer (IR-Prestige-21; Shimadzu Corporation, Kyoto, Japan). For the cases
the FT-IR spectra were analyzed at different temperatures. Here, temperature was
adjusted using a program temperature controller (TXN-700, ST Japan, INC.). The
FT-IR data of swelling microgels were determined using CaF2 windows (30 mm
diameter with 1 mm thickness). The microgel solution was swollen and placed in CaF2
window. Then, another CaF2 window was used to covered and form a sandwiched.
Teflon tape was used to prevent water penetration to the sample. Herein, weight ratio of
freeze-dried microgels and water was 1 by 1 in the microgel solution. The sealed CaF2
windows contained the microgel were set in the US water bath. As shown in Scheme
5-2, the localization of the sealed CaF2 windows was at center in the water bath. The flat
side of the windows was faced toward the transducer side with about 10 cm distance.
Then, the windows having sample solution was exposed to each US for 10 and 60 min.
146
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
Scheme 5-2 Preparation sample for FT-IR measurement and US exposure setting
147
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
After the US was exposed, each FT-IR spectrum was measured immediately within
about 15 seconds. The experiments were carried out 3 times at the same condition with
reproducibility.
5.3 Results and discussion
5.3.1 US influenced thermo-sensitivity of microgels
As shown in Figure 5-1, hydrodynamic diameter of the microgel particles in water was
measured at different temperature from
0 ˚
to
˚ . The measurements were
performed after the aqueous microgel solution was exposed to US in the US water bath
for 10 min to 60 min. For PNM (Figure 5-1-(b)), it was observed that the VPTT was
around 3 ˚ . In addition, there was no difference in the swelling behavior between the
PNM microgel with and without US treatment. Interestingly, PNAM microgel displayed
two-step volume phase transition (Figure 5-1-(a)). The transitions were laid on around
˚
and 36 ˚ . This was due to the presence of hydrogen bonding between >NH
group and –COOH group, indicating that the hydrogen bonding induced the initial
shrinking of the PNAM microgel
[12]
. Therefore, the US treatment of the PNAM
microgel was attributed to two-step phase transition behavior. In contrast to the PNM,
microgel hydrodynamic diameter of the PNAM microgel became slightly large size
from 490 nm to 540 nm before and after the US treatment. The result demonstrated that
148
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
Figure 5-1 Phase transition behaviors of (a) PNAM and (b) PNM (○ heating and (●
cooling without
. (□ heating and (■ cooling with 83 kHz
for 60 min.
149
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
the PNAM microgel could retain a larger amount of water and be swelled by the US
treatment. This was considered that internal hydrogen bonds between the carboxylic
acid and amide groups in the microgel were broken by the US treatment. The results of
the PNAM microgel suggested that the US treatment might break the hydrogen bonds
for de-solvation of water and then hydrophobic segments of NIPAM were gathered after
US treatment
[23]
. But, the PNM microgel having no carboxylic acid segments showed
less sensitive to the US exposure. As seen to the phase transition behaviors of the
PNAM microgel for the US treatment, initial and second shrinking temperatures were
significantly elevated from
˚
to 30 ˚
and from 36 ˚
to 0 ˚ , respectively,
relative to those without US. This phenomenon implied that more thermal energy was
needed to be de-solvation of the internal water from PNAM microgel, which was treated
with US.
It was noted that there was large difference in heating and cooling process, especially in
the PNAM microgel (Figure 5-1 (a)), for the hydrodynamic diameters without and with
the US treatment. This showed that the transition was made by breaking hydrogen
bonds at 20 ˚
and then, de-solvation of water molecules from the microgel was
occurred. It was known that the hydrogen bonding breaking and the de-solvation were
150
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
explained by Nur et al. [9] that the microgels had different water solvation and formation
of hydrogen bonds of the NH group and COOH group in cooling and heating processes.
As seen in Figure 5-1 (a), after the heating-cooling cycle was finished, the
hydrodynamic diameters at 20 ˚C were slightly different in 530 and 540 nm,
respectively, in heating and cooling systems. But, it was confirmed that the
hydrodynamic diameter of the microgel was returned to the original one after 24 hours
was passed after the US exposure. This demonstrated that although the swelling
condition was different in these cases without and with the US treatment, the microgel
could allow to return to their initial arrangement.
As mentioned above, it was clear that US treatment could influence the phase transition
behavior of the PNAM microgel. Therefore, the effect of US frequency and the
irradiation time on the phase transition behavior of the PNAM microgels was examined.
Figure 5-2 shows phase transition behaviors for the PNAM microgel exposed at 28, 45
and 83 kHz US for 1 h and without US. Here, for each US frequency the 50 W output
power was controlled in the water bath. From these results, the 28 and 45 kHz US could
influence the breakage of internal hydrogen bonds for the PNAM microgel at about 28
˚C and 30 ˚C, respectively. However, the 83 kHz US showed at 31 ˚C in the phase
transition temperature. In addition, increase in the hydrodynamic diameter was observed
151
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
Figure 5-2 Temperature effect of hydrodynamic diameters of PNAM microgel
irradiated with (▲) 83kHz US, (■ 5kHz US, (● 8kHz US and () without US.
152
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
in the 83 kHz case, relative to the 28 kHz and 45 kHz cases. This was due to the
hydrogen bonding between NH group and COOH group which was effectively broken
in the 83 kHz US. For the second transition which was attributed to the aggregation of
the NIPAM segments by de-solvation of water molecules from the microgel
environment, each phase transition appeared at higher temperature in the US treatment
but no US treatment was at 36 ˚C.
Figure 5-3. shows dependence of US irradiation time for the 83 kHz US in the range
from 10 to 60 min. The result presented that hydrodynamic diameter increased and
phase transition temperature gradually raised toward higher temperature depending on
the US irradiation time from 0 to 40 min. Then the similar phase transition behaviors of
the PNAM microgel having the 40 and 60 min exposures were observed. Therefore, the
equilibrium between breakage and reformation of hydrogen bonds was reached after the
83 kHz US was irradiated for 40 min.
5.3.2 FT-IR spectroscopic study for US effect on thermo-sensitive microgels
In order to examine the detail of US effect on thermo-sensitive microgels the
measurement of the FT-IR spectra of the water-swollen microgels was carried out, when
the 83 kHz US was irradiated at 20 ºC for 10 min and 60 min. As shown in Figure
5-4-(a), FT-IR spectra of the PNAM microgel in the presence of water displayed
153
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
Figure 5-3 Temperature effect of hydrodynamic diameters of PNAM US irradiation for
(△) 60min, (○ 0min, (□ 0min, (◊) 10min and () 0min.
154
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
considerable difference before and after the US exposure. Especially, hydrogen bonded
COO-H---N(C=O)H stretching broad band around 3860 cm-1 - 2600 cm-1 and >NH and
C=O stretching bands around 1650 cm-1 and 1550 cm-1, increased with the increases of
the US irradiation time from 0 to 60 min. In addition, the OH band intensity at 3400
cm-1 was decreased by the US exposure. This was precise evidence that the free OH
groups of the AA segments were solvated with water molecules by the US treatment.
Here, the free OH meant the presence of the COOH group without forming hydrogen
bonds between the OH group and the COOH group [21, 23] or COOH dimmers [24]. On the
other hand, in FT-IR spectra of the PNM microgel without AA segments, less change
with US exposure was observed as shown in Figure 5-4 (b).This suggested that in the
case of the PNAM microgel, the presence of the AA segments was influenced on the
formation of the hydrogen bond and water solvation.
It was noted that the FT-IR intensity at about 2800-2900 cm-1 was decreased with
increase of the US exposure as shown in Figure 5-4 (a) for PNAM. These bands could
attribute hydrogen bonds for COOH—H2O.
[21]
. However, the PNM microgel had no
change in these wavenumber regions. Therefore, the US was effective for breaking the
hydrogen bonds and then water solvation was occurred after US treatment for the
PNAM. Figure 5-5 shows FT-IR spectra of swollen PNAM microgel after irradiating in
155
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
Figure 5-4 FT-IR spectra of (a) PNAM and (b) PNM with US irradiation in the
presence of water.
156
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
the 83 kHz US for 60 min in the range of 20 ºC and 45 ºC. Here, increasing temperature
was 1 ºC per min. As seen, the FT-IR spectra of the PNAM microgel were less change
in the spectra at each temperature. Namely, the intensity of the OH stretching bands for
the hydrogen bonds of carboxylic acid groups with H2O (COO-H---H2O) in the range of
2000 cm-1 and 3300 cm-1 decreased with increase of the temperature. However, the OH
stretching bands for free H2O around 3420 cm-1 was also increased at
˚ . specially,
their intensity changes were remarkable over 30 ºC. It was noted that at these
temperatures, shrinking the microgel diameter was observed for the PNAM microgel.
The FT-IR spectroscopic data showed that US irradiated to the PNAM microgel could
barely release the internal H2O over the VPTT.
It was also confirmed that the 3400 cm-1 band intensity and other bands could be
returned to the original one after 24 hours. Similar phenomena was previously observed
in aqueous copolymers, P(NIPAM-co-AA)
[20]
in the phase transition behavior and
FT-IR spectra. The OH band intensity in the FT-IR spectra of the copolymers was
returned within 10 min and the behavior was faster than that of the PNAM microgel
which was taken about 24 hours. This difference might be due to the cross-linked gel
structure of the PNAM microgel showing less mobility of the polymer chains. In the
previous result the aqueous copolymers of the P(NIPAM-co-AA)s used for US effect
157
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
Figure 5-5 FT-IR spectra of PNAM with 83 kHz US irradiation for 60 min in the
presence of water with increasing temperature.
158
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
presented that when the US absorption occurred, breaking hydrogen bonds in the
copolymer was also happened and the phase transition appeared. It was considered that
cavitation might be contributed to the decomposition of polymer chains, because of
active chemical species produced with US making the damage. But, it was confirmed
that no decomposition of their polymer chains of the P(NIPAM-co-AA) [20] and another
[23, 25]
was observed by the similar US exposure in the 50 W output power. In addition,
there was no detection on soluble polymer segments in the present work for the PNAM
and PNM by measuring with the similar way. This confirmation indicated that the
contribution of cavitation was very low in the present work. Therefore, US absorption to
the microgel might induce the breakage of the hydrogen bonds in the microgel. The
detail is now progress and will be reported elsewhere in near feature.
5.4 Conclusion
US irradiation had a strong influence on thermal sensitive PNAM microgels. As US was
exposed the hydrodynamic diameter of the PNAM microgel was shifted toward larger
regions and the VPTT was also elevated toward higher temperature side. The FT-IR
spectroscopic data demonstrated that the number of free OH groups of the COOH group
in the microgel increased after US irradiation. Therefore, the effect of US causes that
the hydrogen bonds of the NH and COOH segments were broken, inducing the
159
Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
hydration of the PNAM microgels. Thus, the US exposure was strongly influenced in
the properties of the microgels and its temperature effect in the hydrodynamic diameter.
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Chapter 5 Sono-respond on Thermosensitive Polymer Microgels
162
6 Chapter 6 Summary
Ultrasound technology has been applied in different fields since 1950 when commercial
equipment has been available. From that time until now the application of US has won
importance especially in the chemistry and more recently in sonoprocessing. The
cavitation phenomena produced by US generate high pressure and temperatures inside a
material which could transport the sound wave.
In the present work, it has been studied that US is influenced on properties of aqueous
polymer solution having hydrogen bonded networks, which has influenced on shear
viscosity of the aqueous polymer solutions. After US was exposed to the solution,
several aqueous polymer showed the breakage of hydrogen bonds in the aqueous
solution. In this thesis, the significant decrease in the aqueous viscosity is due to the US
absorption.
Therefore, before demonstration of these interesting data, in Chapter 1 a brave
introduction of sonochemistry and sonoprocessing has been mentioned for
understanding US and its application.
In Chapter 2, it was showed that the US effect was investigated in the shear viscosity
of several natural polysaccharides such as -carrageenan, -carrageenan, and agar. It
163
Chapter 6 Summary
was observed that the US frequency had a significant influence in the change of the
shear viscosity. In addition, during the US exposure, it was noted that the shear
viscosity considerably changes, however after US exposure was stopped the shear
viscosity in each polysaccharides studied retuned to its original value. FT-IR analysis
supported that the hydrogen bonds of carrageenans were broken during the US exposure.
Using Fourier self-deconvolution for the FT-IR spectra without and with US exposure
suggests that the US influenced the hydrogen bonds of water and the OH group of
polysaccharides.
In Chapter 3 describes the study of US effect in aqueous solutions of PVA with
different molecular weight and degree of hydrolysis. The US stimulus showed a marked
decrease of the shear viscosity of the solutions. Subsequently, when US exposure was
stopped, the shear viscosity of PVA reverted to its original value. A new model of US
absorption was proposed on aqueous polymer solution for PVA. Also, FT-IR analyses
on the results of the spectra for the aqueous solution suggest that hydrogen bonding was
breakage in the aqueous polymers and the polymer medium effectively adsorbed US
especially at 43 kHz frequency.
Chapter 4 described that the effect of US on the shear viscosity of water-soluble
polymers such as PVA, PEG, and PAA was studied in aqueous solutions with US. The
164
Chapter 6 Summary
US exposure significantly decreased the shear viscosity of the solutions. When US
exposure was stopped, the shear viscosities of the aqueous polymer solutions reverted to
their original values. Additionally, FT-IR spectra obtained during US exposure showed
that hydrogen bonds in the aqueous polymer solution could be broken, especially at 43
kHz. It was concluded that US exposure influenced hydrogen bonding interactions
between the OH groups of the polymer and water molecules in the aqueous medium.
This finding was supported by US absorption model, which shows the US absorptivity,
US, for each polymer system.
Chapter 5 US irradiation had a strong influence on thermal sensitive PNAM microgels.
As US was exposed the hydrodynamic diameter of the PNAM microgel was shifted
toward larger regions and the VPTT was also elevated toward higher temperature side.
The FT-IR spectroscopic data demonstrated that the number of free OH groups of the
COOH group in the microgel increased after US irradiation. Therefore, the effect of US
causes that the hydrogen bonds of the NH and COOH segments were broken, inducing
the hydration of the PNAM microgels.
As general conclusion, US could be used as external stimuli for changing aqueous
properties of polymeric materials called water soluble polymers. As shown below, this
effect could be explained in the base of the breakage of hydrogen bonds in the aqueous
165
Chapter 6 Summary
polymers by the US absorption. The ability of such material to adsorbed US energy
could be measure by the US absorption model proposed in this thesis. In addition the
chemical changes stimulated with US could be analyzed by FT-IR spectroscopy for
hydrogen bonding breakage and re-forming their bonds in addition with water
absorption to the aqueous polymer systems
166
1 List of Achievements
Publication Papers
1. Ultrasonics Sonochemistry, 20 (2013), 1081–1091. Ultrasound Effect Used as
External Stimulus for Viscosity Change of Aqueous Carrageenans, Josue
Addiel Venegas-Sanchez, Motohiro Tagaya, Takaomi Kobayashi.
2. Ultrasonics Sonochemistry, 20 (2013), 1271–1275. Sono-respond on
Thermosensitive
Polymer
Microgels
Based
on
Cross-linked
Poly(N-isopropylacrylamide-co-acrylic acid), Josue Addiel Venegas-Sanchez;
Takayuki Kusunoki Minoru Yamamoto, Takaomi Kobayashi.
3. Polymer Journal, doi:10.1038/pj.2013.47, Effect of Ultrasound on Changing
Aqueous Viscosity of Several Water Soluble Polymers, Josue Addiel
Venegas-Sanchez; Motohiro Tagaya; Takaomi Kobayashi
Other Related Papers
1． Kazuki Nakasone, Venegas S. Josue Addiel, Motohiro Tagaya, Takaomi
Kobayashi, Ultrasound Effect of Interpenetrated Hydrogels Having
Hydrogen Bonding Networks in Poly(Vinylalcohol)/Poly(2-Hydroxyethyl
Methacrylate) by Using FT-IR Spectroscopy, Transactions on GIGAKU, 1
(2012) 01021/1-6.
167
2 International and National Conference Proceeding
1. The 19th Annual Meeting of JSS, Tokyo, Japan, Ultrasound absorption on
aqueous solution of non-ionic polymers constructing via hydrogen bond
Networks, Venegas Sanchez. Josue Addiel, Ngo Le Ngoc, Kobayashi Takaomi
(October 2010).
2. The 20th Annual Meeting of JSS & The International Workshop on Advanced
Sonochemistry,
Nagoya,
Japan,
Effect
of
ultrasound
on
acrylic
acid-N-hydroxyethylacrylamide copolymers containing hydrogen bond
networks, Venegas Sanchez Josue Addiel, Kobayashi Takaomi (November
2011).
168