Vol. 9 | No. 4 |588 - 596 | October - December | 2016
ISSN: 0974-1496 | e-ISSN: 0976-0083 | CODEN: RJCABP
http://www.rasayanjournal.com
http://www.rasayanjournal.co.in
SYNTHESIS AND CHARACTERIZATION OF SCHIFF BASE
LIQUID CRYSTALS WITH DISPERSED ZnO
NANOPARTICLES-OPTICAL PROPERTIES
1
P.Jayaprada1, M. Tejaswi1, G.Giridhar2, M.C.Rao3, V.G.K.M. Pisipati4
and R.K.N.R Manepalli1*
Department of Physics, The Hindu College, Krishna University, Machilipatnam-521001, India
2
Department of Nanotechnology, Acharya Nagarjuna University, Guntur-522510, India
3
Department of Physics, Andhra Loyola College, Vijayawada-520008, India
4
LCRC-R&D, Department of ECE, K. L. University, Guntur-522502, India
*E-mail: [email protected]
ABSTRACT
Liquid crystalline compounds exhibit more enhanced optical properties with dispersed ZnO nanoparticles. In the
present work 1wt% ZnO nanoparticles are dispersed in liquid crystalline Schiff base 10O.Om compounds (m=3,4
and 5). The Differential Scanning Calorimetry (DSC) technique is used to measure the phase transition
temperatures. The characterization of nanoparticles is carried out by various spectroscopic techniques like UltraViolet Visible Spectroscopy(UV), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier
Transform Infra Red Spectroscopy (FTIR). Textural determinations of the synthesized compounds are recorded by
using Polarizing Optical Microscope (POM) connected with hot stage and camera. The results show that the
dispersion of 1wt%ZnO nanoparticles in 10O.Om compounds exhibit NC phases as same as the pure compounds
with reduced clearing temperatures as expected and the nematic thermal ranges are increased slightly.
Keywords: Synthesis, POM, DSC, Nano dispersion, UV, XRD, SEM and FTIR.
© RASĀYAN. All rights reserved
INTRODUCTION
Liquid crystals (LCs) are partially ordered and physical anisotropic materials. These materials are very
sensitive to different external effects, for example electric, magnetic and thermal fields, surfaces,
boundary conditions, flow etc. Most applications of these materialism LCs technique and LCs technology
depend upon their thermo-optical, electro-optical and magneto-optical properties1–4. For the technical and
technological applications of LCs, information about the optical anisotropy, refractive and polarization
properties and also about their temperature behavior is important .Liquid crystalline materials appear as
perfect candidates for the synthesis and self-assembly of nanoscale materials as the liquid crystalline state
combines order and mobility at the molecular, nanoscale level. Composed of anisotropic molecules, LCs
respond to external fields and interact with surfaces, thus influencing their structure and properties5. In
recent years, liquid crystalnanoparticle (LCNP) composites have drawn significant attention and are now
one of the hot topics in LC research6-7. A broad area of research topics from fundamental physical,
biological and chemical phenomena to material science has been addressing by the scientific society at
the nanoscale8-10. The minute addition of nanoparticles (NPs) to LC materials has improved many special
characteristics in the form of frequency modulation response11, non-volatile memory effect12, fast electrooptic response13, low driving voltage14 and so on. In the present generation, nanoparticles of transition
metal oxides (TMOs) are the main areas of materials research due to their wide applications in many
areas. In spite of these TMOs, zinc oxide nanoparticles are used in numerous applications like UV
absorption, antibacterial treatment andso forth15–18. Zinc oxide, with its unique physical and chemical
properties, such as high chemical stability, high electrochemical coupling coefficient, broad range of
radiation absorption and high photo stability, is a multifunctional material19-20. The piezo and pyroelectric
SCHIFF BASE LIQUID CRYSTALS P. Jayapradaet al.
Vol. 9 | No. 4 |588 - 596 | October - December | 2016
properties of ZnO mean that it can be used as a sensor, converter, energy generator and photo catalyst in
hydrogen production21-22. The doping zinc oxide NPs to nematic liquid crystals considerably decreased
threshold voltage and this may help the lower energy consumption of liquid crystals devices23. Moreover,
zinc oxide NPs increased the thermal range of the LC nematic phase24 and enhanced orientation of liquid
crystals25. ZnO nanosystem may be of important relevance in the context of nanomedicine, where
targeted treatment of biological systems at molecular level is a necessity26.
EXPERIMENTAL
Synthesis of ZnO nanoparticles–High Pressure Combustion synthesis (High Pressure Autoclave)
Take a known amount (3 g) ofZnO dissolved in 10ml of conc. HNO3 solution and 10 ml H2O in 100 ml
RB flask. The solution is stirred at ambient temperature for 1hour. Then add Urea (reducing agent/fuel)
which decomposes macro-molecules into nanoparticles. Now add 10 mol% flux (Boric Acid) and stirred
the solution for 0.5hour. Later keep the entire solutions into high pressure reactor at 120-130oC
maintaining a pressure of 200 Kg/cm2 for 30min. At this stage urea decomposes the entire solution in to
ZnO nanoparticles. Then wash the resultant powder with methenol/water 5 to 10 times and dried and
finally ZnO nanoparticles of size nearly 80nm are obtained. These nanoparticles are further characterized
by UV-Visible Spectroscopy and SEM experimental techniques.
Synthesis of 10O.Om compounds
The synthesis of 10O.Om compounds are synthesized as follows. The respective p-ndecyloxybenzaldehyde and the corresponding alkoxyanilines are taken in equi-molar proportions in
absolute ethanol and refluxed for four hours in the presence of few drops of glacial acetic acid. After
refluxing the reactions for four hours, the solvent was removed by distillation under reduced pressure.
The crude sample was subjected to repeated re-crystallization from absolute ethanol in cold to give the
pure 10O.Om LC compound.
Dispersion of ZnO nanoparticles in 10O.Om compounds
After that the 10O.Om compounds which are proposed are dispersed with nanoparticles of zinc oxide,
obtained from Sigma Aldrich Laboratories and these are used without any furtherpurification. For
uniform dispersion of nanoparticles(ZnO) in to N-(p-n-decyloxybenzylidene) p-n-alkoxy anilines
(10O.Om) LC compounds, first dissolved in ethyl alcohol, stirred well about 45minutes and later
introduced in the isotropic state of mesogenic material in the ratio of 1wt%.
Where, m=3, 4 and 5
After cooling the ZnO dispersed N-(p-n-decyloxybenzylidene-)p-n-alkoxy anilines is subjected to study
the textural and phase transition temperatures using polarizing optical microscope with the hot stage in
which the substance is filled planar arrangement in 4 µm cells and these can be placed along with the
thermometer described by Gray27. DSC (Perkin Elmer Diamond DSC) is used to obtain the transition
temperatures and the enthalpy values before and after synthesis in exothermic as well as endothermic
regimes. FTIR is a powerful tool to identify the vibrational bands of various organic bonds with definite
frequencies. Along with the categorization, type of chemical bond in a molecule, organic and inorganic
chain links are also able to recognizable with the produced infrared transmission spectrum. XRD
technique is used to determine the size of ZnO nanoparticles which are dispersed in LC compounds and
also to confirm the crystalline structure of the as synthesized compound. The presence of ZnO
nanoparticles in 10O.Om LC compounds were studied by using SEM and EdS data.
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RESULTS AND DISCUSSION
Polarizing Microscope
The transition temperatures and textures observed at 10x (SP - Achro) magnification by Polarizing
Microscope (SDTECHS-SDVPM 2727) in pure 10O.O3 is shown in Fig.1a, Fig.1b and Fig.1c while that
of 10O.O3with dispersed 1 wt% of ZnO nanoparticles shown in Fig.2a, Fig.2b and Fig.2c respectively.
The transition temperatures and textures of 10O.O4 pure and thatof dispersed 1 wt% of ZnO nanoparticles
are shown in Fig.3a, Fig.3b and Fig.3c and Fig.4a, Fig.4b and Fig.4c respectively. The thermal ranges of
nematic and smectic C phases are changed slightly due to the dispersion of nanoparticles and the textures
of the LC phase’s changes by the self assembly of nanoparticles. The DSC thermograms are shown in the
Fig.5, Fig.6 and Fig.7. It is observed that the transition temperatures are lower and nematic thermal ranges
increased while 1wt% ZnO nanoparticles dispersed in 10O.Om compounds.
10OO3 PURE
(a.) Nematic 104.9 °C
(b.) Smectic-A 88.4 °C
Fig.-1
(c.) Solid 83.30 °C
(b.) Smetic-C 84.7 °C
Fig.-2
(c.) Solid 77.9 °C
(b.) Smectic-C 84.7 °C
Fig.-3
(c.) Smetic-B-Solid 75.0 oC
10OO3+1wt %ZnO nps
(a.) Nematic 103.2 °C
10OO4 PURE
(a.) Nematic 105.1 °C
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10OO4+1wt%ZnO nps
(a.) Nematic 105.0 °C
(b.) Smectic-C 93.4 °C
Fig.-4
(c.) Solid 73.0 °C
DSC Thermograms
Fig.-5: DSC Thermogram of 10O.O3 + 1wt% of ZnO nanoparticles
Ultraviolet –Visible (UV) Spectroscopy
The Fig.8 shows the UV-Visible spectra of ZnO nanoparticles dispersed 10O.O5 LC sample. It is
observed that the spectrum for pure 10O.O5 does not exhibit any absorption peaks in the wavelength
range of 350 nm–400 nm. However, the spectrum of nano dispersed 10O.O5 shows the significant peak at
373 nm, which are the characteristic peak ZnO nanoparticles. So, the UV-visible spectral study confirms
the presence ZnO nanoparticles in the prepared nano doped LC.
FTIR Studies
The IR specta of pure 10O.O3 and with dispersed 1 wt % ZnO nanoparticles is shown in Fig.9. The
compound is stable at room temperature. The IR frequencies in solid state which are correlated in bonds
with pure compound 10O.O3 the assigned bonds corresponding to the resultant frequencies from the
spectra are tabulated. Due to the excitation of both molecular vibrations and rotations and absorptions of
electrmagnetic radiation causes the formation of absorption bands in the IR spectra which are useful to
explain the bonding interaction of the molecules. in both spectra exhibit a strong electrmagnetic
absorption at 2920.62 cm-1, 2852.71 cm-1 and 2919.03 cm-1, 2853.50 cm-1 corresponding to the OH bond.
The absorption band at1606.11 cm-1, 1573.21 cm-1, 1507.39 cm-1 and 1606.11 cm-1, 1573.21 cm-1,
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1513.37 cm-1 corrsponding to ring stretching. The band at 1246.12 cm-1 and 1246.12 cm-1 corresponding
to aromatic ring stretching. The band at 1309.28 cm-1 and 1306.28 cm-1 corresponding to dimer. The band
at 1168.34 cm-1 and 1165.34 cm-1 corresponding to CH-OH bending. The band at 778.10 cm-1 and 775.11
cm-1 corresponding to aromatic ring structure. The band at 640.15 cm-1 and 640.15 cm-1 corresponding to
OH bond. The peak at 1690.59 cm-1 corresponds to ZnO stretching28. The assigned peak values are in
accordance with literature values.29-31
Fig.-6:DSC Thermogram of 10O.O4 + 1wt% of ZnO nanoparticles
Fig.-7: DSC Thermogram of 10O.O5 + 1wt% of ZnO nanoparticles
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SEM Studies
A small amount of ZnO nanoparticles and nanoparticles dispersed LC compounds are taken on sample
holder for the scanning electron microscopy. TheSEM provides the investigator with a highly magnified
image of the surface of a material as the present sample contains electrons; which are needed for getting
SEM image. SEM gives not only topographical information but also gives the information regarding the
composition of the elements in the material32, 33. The SEM images along with the EDS data of pure ZnO
nanoparticles and 10O.O5 with dispersion of ZnO nanoparticles are shown in the Fig.10, Fig.11 and
Fig.12, Fig.13 respectively. From the Fig. 12 the size of the ZnO nanoparticles are found to be 50 – 80
nm. From EDS data of Fig. 12, it is also evidenced the presence of ZnO nanoparticles dispersed in the
compound 10O.O3 is well established.
Fig.-8: UV-visible spectra of pure 10O.O5, Pure ZnO nanoparticle and ZnO nanoparticles dispersed in 10O.O5.
Fig.-9: FTIR of10O.O3 pure and with dispersed 1wt% ZnO nanoparticles
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Fig.-10: EDS data of pure ZnOnanoparticles
Element
OK
Zn L
Fig.-11: SEM photograph
Weight%
37.85
62.15
Fig.-12: EDS data of 10OO3 + 1 wt % ZnO Compound
Element
CK
NK
OK
Zn L
Weight%
61.94
24.45
13.59
0.01
Atomic%
71.34
28.66
Fig.-13: SEM photograph
Atomic%
66.52
22.52
10.96
0.00
XRD Studies
The XRD data of 10O.O4 with dispersed 1 wt % of ZnO nanoparticles is shown in Fig.14. In comparison
of JCPDF data, the peaks are well resolved and are matched with JCPDF card number: 01-081-0-0681
clearly evidenced the existence of ZnO nanoparticles. By using Schrrer’s Formula, t = kλ/ βcosθ, the size
of ZnO nanoparticle is found to be 78.4 nm, Λ=1.54 Ao, β= FWHM, Peaks at 18.114º, 47.0586o, 56.4068o
and 62.133o respectively resembles the existence of ZnO nanoparticles dispersed in 10O.O4 LC
compound.
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Peak List
01-081-0681
20
30
40
50
60
70
80
90
Position [°2Theta]
Fig.-14: XRD data of 10OO4 with 1 wt % ZnO nanoparticles
CONCLUSIONS
With the present results we have demonstrated the dispersion of Zno nanoparticles in LC 10O.Om
changing of their textures, phase transition temperatures and shifts in vibrational bands by using
Polarizing Microscope, Differential Scanning Calorimeter and Fourier Transform Infra Red techniques
respectively. The transition temperatures obtained from polarizing microscope are in good agreement
with those obtained from DSC. The presence Zno nanoparticles dispersed in 10O.Om is also confirmed
by the EDS data of SEM and UV-Visible spectrometry.X-Ray diffraction confirms that no alteration of its
structure and also the existence of the ZnO nanoparticles.X-ray diffraction data is also confirms the
existence of ZnO nanoparticles without altering the host’s structure having ZnO nanoparticle size of 78.4
nm from sherrer’s formula which is exactly agreed with that from SEM data.
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ACKNOWLEDGEMENTS
The corresponding author R.K.N.R. Manepalli is thankful to the UGC for grant 42-784/2013 (SR).
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[RJC-1487/2016]
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