Nanocomposite silver/poly(ethylene oxide)-like plasma polymers
prepared by plasma-assisted vacuum evaporation and magnetron
sputtering
Dmitry Arzhakov1, Ivan Gordeev1, Andrei Choukourov1, Anna Artemenko1, Ondřej Kylián1, Jaroslav Kousal1,
Oleksandr Polonskyi1, Josef Pešička2, Danka Slavínská1 , Hynek Biederman1
1
Charles University in Prague, Faculty of Mathematics and Physics, Department of Macromolecular Physics, V
Holešovičkách 2, 180 00 Prague, Czech Republic
2
Charles University in Prague, Faculty of Mathematics and Physics, Department of Physics of Materials, Ke
Karlovu 5, 121 16 Prague, Czech Republic
Abstract: Nanocomposite Ag/poly(ethylene oxide)-like plasma polymers were
prepared by simultaneous vacuum thermal degradation of poly(ethylene oxide)
(PEO) and RF magnetron sputtering of silver. At constant discharge power,
nanocomposites with different silver content were fabricated by varying the
evaporation rate of PEO. Chemical composition, structure, optical and
bioadhesive properties of Ag/PEO-like nanocomposites were studied by XPS,
FTIR, UV-Vis, QCM and TEM techniques. Obtained filling factors ranged from
0.8 % to 28.0 % whereas relative fraction of ether groups in polymeric phase
varied between 79% and 54%. In general, the increase of silver content led to
reduced retention of the PEO structure and as a consequence to the loss of nonfouling properties. Structural changes were also studied upon the contact of the
nanocomposites with water. Nanoparticles of silver were found to diffuse within
the polymeric matrix with following coalescence and formation of larger metallic
structures.
Keywords: Poly(ethylene oxide), plasma polymer, nanocomposite, magnetron
sputtering
1. Introduction
Nowadays, there is a growing interest in plasmadeposited thin films which show biocompatibility
and are able to prevent microbial adhesion. Different
approaches to inhibit bacteria growth have been
proposed [1]. PEO is one of the most well-known
biocompatible materials [2]. Several methods have
been used to obtain the non-fouling films from PEO.
Recently, glow discharge-based methods have been
given a thorough consideration for fabrication of
PEO-like plasma polymers [3-7]. On the other hand,
silver is one of conventional antibacterial reagents. It
is believed that Ag can prevent bacterial enzyme
activity [8, 9]
Several research groups have focused their attention
on plasma deposition of nanocomposite Ag/PEOlike plasma polymers [10-14] with motivation to
combine the non-fouling properties of PEO with the
anti-bacterial properties of silver. For maintaining
the non-fouling nature of plasma-deposited PEO-like
films it is necessary to reach the highest retention of
the C-O-C groups in plasma polymer. It is usually
achieved when small discharge power of several
watts is used. For magnetron sputtering, however,
higher powers are favourable to ensure sufficient
supply of silver. On the other hand, the higher power
may deteriorate the retention of the C-O-C groups.
This work presents a method of obtaining Ag/PEOlike plasma polymers by simultaneous magnetron
sputtering of Ag and vacuum evaporation of
conventional PEO. The possibility to fabricate the
films with different filling factors of silver, yet with
high retention of the PEO structure is discussed.
measurements by using pre-defined values of
deposition rates of pure silver and PEO plasma
polymers. The deposition parameters are
summarized in Table 1.
2. Experimental setup
3. Results and Discussion
The experimental arrangement was described in
detail in [15-16]. Granules of conventional PEO
were loaded into a copper crucible, which was
heated by electric current. The crucible was placed 4
cm above a magnetron equipped with a silver target
(figure 1). A radio frequency (Dressler Ceasar
13.56MHz) generator was used to deliver power to
the magnetron. A quartz crystal microbalance
(QCM) was placed in plane with the substrates 10
cm above the crucible to control the deposition rate.
The vacuum chamber was brought to a base pressure
of 2х10-3 Pa by rotary and diffusion pumps. The
experiments were performed with argon used as a
working gas. The pressure of 1 Pa and 5 cm3 (STP)
min-1 flow rate were used. The discharge power was
kept constant at 15 W. To obtain the films with
different content of Ag, the deposition rate of PEO
was varied by varying the temperature of the
crucible. Volume fraction of silver, also called
filling factor f, was determined from the QCM
Table 1. Deposition parameters and filling factor of silver in the
nanocomposite Ag/PEO-like plasma polymer films.
Process
Power
W
QCM,
frequency
shift Hz/min
Deposition
rate
nm/min
Ag
15
5
0.3
Ag
PEO
+
QCM,
filling
factor
vol. %
100.0
15
17
2.4
28.0
15
25
5.1
13.0
15
60
20.0
2.0
15
100
38.0
0.8
COC
54 %
CC/CH 31 %
Fill factor = 13,0 %
COC
61 %
CC/CH 25 %
Fill factor = 2,0 %
COC
75 %
CC/CH 15 %
Fill factor = 0.8 %
COC
79 %
CC/CH 14 %
CPS
Figure 1. Experimental setup: Q – quartz crystal microbalance,
C– crucible with PEO; M – magnetron; T– silver target.
Fill factor = 28,0 %
290
288
286
284
282
Binding Energy (eV)
Figure 2. The C1s XP spectra of Ag/PEO-like nanocomposites
prepared with different evaporation rate of PEO.
Figure 2 shows the C1s peaks of the XPS spectra of
the Ag/PEO-like plasma polymers with four
different filling factors of Ag. The C 1s peak was fit
by four components, namely C0 (C-H, C-C:
BE=285.0 eV), C1 (C-O-C: BE=286.5 eV), C2
(C=O: BE=287.8 eV), C3 (O-C=O: BE=289.2 eV).
The values of filling factors are also given for
clarity. Obviously, the amount of Ag and the
concentration of the C-O-C groups are related
inversely.
The relative fraction of the C-O-C species decreases
from 79 to 54 % with increasing silver content from
0.8 % to 28.0 %. The films with high silver content
(low evaporation rate of PEO) show the loss of the
PEO character because of the increased specific
power of the discharge, i. e. the power per mass unit
of the precursor. Such behavior is analogous to that
observed earlier in [10-14]
Transmittance (%)
100
rate of PEO. Increase of the silver content leads to
loss of non-fouling properties of coatings as
measured by QCM in terms of fibrinogen
adsorption.
0.8%
80
2%
60
13%
40
Pure Ag
28%
20
0
200
300
400
500
600
700
800
wavelength (nm)
Figure 3. The UV–Vis transmittance of the nanocomposite
Ag/PEO-like plasma polymers with different filling factors.
The UV-Vis transmission spectra given in Figure 3
show that the nanocomposite Ag/PEO-like plasma
polymer films are optically active in the visible area.
The strong absorption peaks can be seen which are
induced by the surface plasmon resonance (SPR)
effect.
This effect is
characteristic for
metal/dielectric nanocomposites when collective
resonant oscillations of electronic gas in metals
(plasmons) are excited upon interaction with
electromagnetic field. The increase of silver content
leads to intensification of the absorption.
The main motivation for fabrication of the Ag/PEOlike plasma polymer films is their possible use in
biomedical applications. Therefore, their behaviour
in contact with water is of a great importance and it
was also studied on example of the film with 13% of
Ag. Figure 4a shows the distribution of the silver
nanoparticles in plasma polymer matrix in a dry state
as observed by TEM. It can be seen that silver
nanoparticles tend to coalesce into bigger
agglomerates which indicates their ability to diffuse
in the bulk of the plasma polymer. Significant
degree of flexibility of the PEO molecular segments
can therefore be expected. The particles are of
spherical shape and their size distribution is rather
broad ranging from 2 nm to 45 nm.
Immersion into water for two days has tremendous
effect on the structure of the film (figure 4b). Silver
undergoes crystallographic transformations and form
larger monocrystalline structures of triangular shape.
Figure 5 shows the adsorption kinetics of fibrinogen
on the nanocomposite Ag/PEO-like plasma polymer
films, which were prepared at different evaporation
Figure 4. TEM images of the Ag/PEO-like nanocomposite with
13% of Ag before wetting a) and after wetting b).
In the case of high evaporation rate of PEO (0.8% of
Ag), the frequency of QCM does not change with
time. This proves that the surface possesses the nonfouling properties. It was shown previously that in
the case of PEO-like plasma polymers about 70%
retention of the C-O-C groups is required for the
film to behave non-fouling [18]. Here, the film with
2% of Ag adsorbs the protein even though the
concentration of the C-O-C groups in the plasma
polymer is still at 75%. Apparently, silver reveals
strong affinity to fibrinogen and introduction of as
low as several percent of silver overrides the nonfouling properties of the plasma polymer. Strong
adsorption of fibrinogen by the film with 28% of Ag
is therefore given by both high content of silver and
low content of the ether groups
79% COC
0.8 % Ag
-20
-40
-60
75% COC
2 % Ag
Protein Added
Delta Frequency (Hz)
0
[4] D. Beyer, W. Knoll, H. Ringsdorf, J.H. Wang,
R.B. Timmons, P. Sluka, J. Biomed. Mater. Res. 36
(1997), 181–189
54% COC
28 % Ag
-80
-100
0
20
40
60
Time (min)
Figure 5. Adsorption of fibrinogen on the Ag/PEO-like plasma
polymer nanocomposites.
4. Conclusions
Nanocomposite Ag/PEO-like plasma polymer films
were prepared by simultaneous vacuum thermal
degradation of polyethylene oxide and RF
magnetron sputtering of silver. This method was
shown to be good at obtaining nanocomposites with
different filling factor of silver and with more than
75% retention of the C-O-C groups in polymeric
phase. Nanoparticles of silver were found to be
relatively mobile and able to form large monocrystal
structures when in contact with water. Increasing
silver content leads to loss of non-fouling properties
of the nanocomposites.
5. Acknowledgements
The work was supported by the grant SVV-2011263305 and by Academy of Science of the Czech
Republic through the grant KAN 101120701.
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