Date post: | 17-May-2017 |
Category: |
Documents |
Upload: | lathoifulisyaroh |
View: | 226 times |
Download: | 0 times |
31 Advances in Polymer Science and Technology: An International Journal 2013; 3(3): 31-35
ISSN 2277 – 7164
Original Article
Studies on Polymer dispersed Liquid Crystals
Rita A.Gharde1*, Jyoti R. Amare
1, Santosh A. Mani
2
1. Department of Physics, University of Mumbai, Mumbai 400098
2. K. J. Somaiya College of Engineering, Mumbai 400077
Email: [email protected], [email protected]
Received 02 August 2013; accepted 22 August 2013 Abstract
PDLC consists of Liquid Crystal (N+Ch) droplets that are dispersed in a monomer or prepolymer. These materials are
simply a combined application of polymer and Liquid crystal PDLC and their electro-optic have been extensively studied
during last decades. By using the principle of refractive index matching reorientation of nematic droplets in polymer film
can be used in the display industry.
Recently, liquid crystal doped with polymer is used to enhance the physical properties of the LCs materials. In this paper
we present the changes in transition temperature along with new phase transition temperature in polymer liquid crystal.
Measurements are performing for both heating and cooling of samples. Texture observation and spectroscopic-techniques
are used to characterize the other properties of the PDLC samples. Fourier Transform Infra Red spectroscopy has become
the most informative tool in the study of confirmation of LC crystalline material.
The polymer doped liquid crystal suspension can be used as a new liquid crystalline material that does not require any
additional alignment processing or treatment. Our results will provide new opportunity for scientific community and their
uses in advanced technology development.
© 2013 Universal Research Publications. All rights reserved
Keywords: Polymer Dispersed Liquid Crystals (PDLCs), Polarizing Microscopy Study (PMS), Fourier Transform Infrared
(FTIR) Spectroscopy.
1. Introduction: Liquid crystal (LC) is a thermodynamic stable phase
characterized by anisotropy properties without the
existence of a three-dimensional crystal lattice. LCs lies in
the temperature range between the solid and isotropic liquid
phase, hence the term mesophase. Composites based on
liquid crystals (LCs) have attracted much attention over a
number of years because of their unique optic, electro- and
magneto-optic properties and novel display applications.
Polymer dispersed liquid crystals (PDLC) is a typical
example of this composite LCs. PDLC’s consist of small
nearly uniform sized (down to sub- micrometer) droplets of
a LC in a solid polymer matrix. They are formed during the
Phase separation caused by a polymerization of organic
monomers in a liquid-crystal–monomer mixture. PDLC’s
are attracting attention because of their application in
scattering LC displays and light shutters. For many
applications of PDLC, a proper selection such as size,
shape, preparation methods of mesophase range of and
existence of phases at a desired temperature. PDLC
materials generally have several common characteristics;
one of the characteristics is the transition temperature
which is here measured over temperature range phases. To
achieve useful temperature range, various mixtures can be
used. The miscibility of the low molar LC is important both
for the identification of various liquid crystalline phases
and for the preparation of mixtures with well defined phase
transitions. Arnold, Scakmann and Demus developed the
miscibility rules [7, 8]
which can be summarized as follows:
1) If two LCs are miscible, they are isomorphic and
therefore belong to the same type of mesosphase.
2) If two LCs are isomorphic, they need not necessarily
be miscible
When two compounds are isomorphic within a certain
mesophase, both their thermal transition temperatures and
corresponding thermodynamic parameters exhibit
continuous dependence on their composition, this means
that both the components of mixtures behave like an ideal
solution. There are several methods used to identify
characterization the various liquid crystalline phases Viz.
Polarizing microscopy (PMS), Fabry - Perot Scattering
Studies (FPSS), X- Ray Diffraction (XRD), Fourier
Transform Infrared (FTIR) Spectroscopy, Differential
Scanning Calometry (DSC)/ Differential Thermal Analysis
(DTA) etc. We studied physical properties of 4 –
cynophenyl –4n hexyl benzoate (Solid → Nematic →
Available online at http://www.urpjournals.com
Advances in Polymer Science and Technology: An International Journal
Universal Research Publications. All rights reserved
32 Advances in Polymer Science and Technology: An International Journal 2013; 3(3): 31-35
Isotropic) and Cholesteryl pelargonate (Smectic →
Cholestric → Isotropic). The study of phase transition of
thermotropic liquid crystal is done by polarizing
microscopy. The phase transition of liquid crystal between
various mesomorphic forms occurs at a thermodynamically
defined temperature as the liquid crystal undergoes a
change in internal order at the point of phase transition. 4 –
Cynophenyl – 4n – hexyl benzoate exhibit mesophases of
nematic phases.We used the FTIR technique for formation
of new functional group. PMS for texture studied and
comparison of transition temperature. In addition to this,
we observe Refractive index of entire sample in pure as
well as doped form.
2. Experimental Details:
In this paper we used the sample of the CLCs Cholesteryl
pelargonate (97%) (A) And 4 – cynophenyl – 4n hexyl
benzoate (97%) (B) and their mixtures with and without
monomer (M) in appropriate proportions by weight [A+B]
and [A+B+M] have been investigated. Phase transition
temperatures are found in Polarizing Microscopy. From the
study of PMS we observe the textures and analyzed the
transition temperatures as well as nature exhibited by liquid
crystal phases. The Phase Transition temperature shows
more complex behavior at the lower heating cycle and
diverse concentrations. We observed, some interesting
phases like, Structural changes due to various
concentrations at various excitations were studied by FTIR.
We found the different functional groups which are present
in a molecule like all over the mixtures. The compounds
show spectra in which many peaks spread over the wide
range of frequencies (1500cm-1
-3000 cm-1
). FTIR analysis
showed in mixture a strong absorption peak (between 1600
– 1700) of chloride indicating group RCH=O, was stretch
and appear two peaks. A small peaks occurs at (between
2500 – 3000) indicating –NH absorption.
3. Experimental Techniques:
3.1 Polarizing Microscopic Studies (PMS):
Polarizing microscope is the most widely used method in
identifying different phases. LC is placed between two
glass cover slips. Depending on the boundary condition and
the type of phase, varies textures which are characteristics
of a phase are observed. Usually the textures change while
going from one phase to the other. Polarizing microscopy is
powerful tool when used in combination with miscibility of
binary mixtures. LC phases possess characteristic textures
when viewed in polarized light under a microscope. These
textures, which can often be used to identify phases, result
from defects in the textures. Polarizing Microscopy is used
for various phases like Nematic, SmA, SmB. SmC,……..
When LC, goes from a solid to liquid crystal phase, the
degree of length order decreases. This is expressed by a
decrease in order parameters. In case of orientational
disorder it is possible to see changes between different LC
phases of heating and cooling from the textures.
3.2 Fourier Transform Infrared Spectroscopy (FTIR):
FTIR is powerful tool for identifying types of chemical
bonds in a molecule by producing an IR absorption
spectrum. FTIR is most useful for identifying chemicals
that are either orgaic or inorganic. It is used to identify
chemicals form spills paints .polymers, drugs, coating and
contaminates. It can be applied to the analysis of types of
chemical bonds i.e. functional groups. It is a chemical
analytical technique that measures the infrared intensity Vs
wavelength of light the IR is divided into three regions
i.e. far infrared ( 4.- 400 cm-1
) , mid infrared ( 400 - 4000
cm-1
) and near infrared (4000 – 14000 cm-1
) IR
spectroscopy works because chemical bonds have specific
frequencies at which they vibrate corresponding to energy
levels. The FTIR spectroscopy detects the vibration
characteristics of chemical functional groups in sample,
when infrared light interacts with matter, chemical bonds
will stretch, contract and bend .So chemical functional
group absorbs IR radiation in a specific wave number range
e.g. C = O stretch of carbonyl group appears at around
1700 cm-1
. Hence the co-relation at band wave number
position with chemical structure is used to identify a
functional group in a sample.
3.3 UV-VIS Spectrophotometer: Ultraviolet–visible spectroscopy or ultraviolet-visible
spectrophotometer (UV-VIS or UV/VIS) refers to
absorption spectroscopy or reflectance spectroscopy in the
ultraviolet-visible spectral region. This means it uses light
in the visible and adjacent (near-UV and near-infrared
(NIR)) ranges. The absorption or reflectance in the visible
range directly affects the perceived color of the chemicals
involved. In this region of the electromagnetic spectrum,
molecules undergo electronic transitions. This technique is
complementary to fluorescence spectroscopy, in that
fluorescence deals with transitions from the excited state to
the ground state, while absorption measures transitions
from the ground state to the excited state.
3.4 Refractive Index (R.I.):
In optics the refractive index n of a substance is a number
that describes how light, or any other radiation, propagates
through that medium. Its most elementary occurrence is in
Snell's law of refraction, n1sinθ1= n2sinθ2, where θ1 and θ2
are the angles of incidence of a ray crossing the interface
between two media with refractive indices n1 and n2.
Brewster's angle, the critical angle for total internal
reflection, and the reflectivity of a surface also depend on
the refractive index, as described by the Fresnel
equations.[1]
Refractive index of materials varies with the
wavelength. In opaque media, the refractive index is a
complex number: while the real part describes refraction,
the imaginary part accounts for absorption. The concept of
refractive index is widely used within the full
electromagnetic spectrum, from x-rays to radio waves. It
can also be used with wave phenomena other than light. In
this case the speed of sound is used instead of that of light
and a reference medium other than vacuum.
4. Result and Discussion:
4.1 PMS Observations:-
33 Advances in Polymer Science and Technology: An International Journal 2013; 3(3): 31-35
4.2 FTIR Observations:
34 Advances in Polymer Science and Technology: An International Journal 2013; 3(3): 31-35
4.3 UV-VIS Observations:
Observation Table for FTIR Analysis:
The peaks and corresponding bonds for composite liquid crystal dispersed with Monomer is shown in Table 1.
Table 1 Sample Peak Wavelength Range Bond
A+Monomer &
Pure A
735.87 600-900 O-H
1004.966 1000-1100 Alcohol, Anhydride
B+Monomer &
Pure B
1178.56 1050-1300 C-O Alcohol
1415.81 1340-1470 C-H Alkanes
1601.95 1600-1700 C=O Aldehyde
A+B+Monomer &
Pure A+B
647.15 600-700 C=CH
681.87 690-900 O-H Phenols
1377.23 4340-1470 C-H Alkanes
1601.95 1600-1700 C=O Aldhydes
3103.53 3100-3200 Ammonium, Amide
35 Advances in Polymer Science and Technology: An International Journal 2013; 3(3): 31-35
The peaks and corresponding bonds for composite liquid crystal dispersed with Monomer for UV – VIS is shown in Table
2
Table 2. Observation Table for UV-VIS
Sr. No. Mixture of Sample UV
1
Mixture at different concentrations
A(100%) 283, 206
2 B(100%) 285.5, 211.5
3 A( 50%) +B (50%) 288,237
1 Polymer dispersed LC at different
concentrations
A(100%) +M 284, 210
2 B(100%) +M 285, 211
3 A( 50%) +B (50%) +M 285
4. Refractive Index Observations:
The refractive Index for composite liquid crystal dispersed
with Monomer is shown in Table 3.
Table 3 Observation Table for R. I
This change in the refractive index can be used as guiding
medium for light propagation.
5. Conclusions: Cholesteric-nematic phase transitions can be induced in
such compensated mixtures thermally. We found some
texture for the concentration of pure and with the PDLC
mixture was confirmed by PMS. FTIR analysis showed a
strong absorption peak (between 600-1700) in mixture.
Also we observe changes in refractive index for PDLC
which can be used as guiding medium.
6. Acknowledgements:
We would like to acknowledge the help and encouragement
given to us by Prof. D. C. Kothari Head, Department of
Physics, University of Mumbai. We are also thankful to Dr.
Shubha Pandit, Principal, K.J. Somaiya College of
Engineering, Mumbai for her help and motivation.
References 1. "Investigation of a AFLCs using Fabry-Perot Etalon"
Liquid Crystals: Chemistry, Physics, and Applications,
SPIE Vol.4759, Poland (2002) S. J. Gupta, R. Gharde
& A. Tripathi.
2. "Phase Transition Temperatures of Liquid Crystals
Using Fabry-Perot Etalon" Molecular Crystals &
Liquid Crystals; vols364-368 (2001) S. J. Gupta, R.
Gharde & A. Tripathi.
3. “Fabry Perot Scattering Studies of Mixtures of
Cholesteryl Liquid Crystals“,Gupta Sureshchandra
J.,Rita A. Gharde,et.al,Journal of Optics,Vol.34
No.2,ISSN 0972-8821,pg.82,April-June 2005
4. “Liquid crystals The fourth state of matter” by franklin
D. Saeva
5. “Introduction to liquid crystal chemistry and Physics”
by Peter J. Collings.“Handbook of liquid crystal” by
Patel & Peter J. Collings,
6. Arnold H and Sackmann H Z, Z phys chem., 213 137
(1960a).
7. Demus D Deile S, Grande S and Sackmann H Z,
“Advances in liquid crystals”: 6th
edition by
G.H.Brown (London: Academic), 1(1983).
8. “Polymer material macroscopic properties and
molecular interpretation”J.L.Halary,F.Lauperetre and
L.Monnerie; Published by Wiley
Source of support: Nil; Conflict of interest: None declared
Sr
No. Sample
R.I. of Pure
Sample
R.I with
Monomer
1 A 1.448 1.482
2 B 1.439 1.493
3 A+B 1.443 1.441