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: jyo_cl2003@yahoo.co.in, samphy2013@gmail.com

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 →

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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