Effect of temperature on the optical and electro‐optical properties of poly(methyl methacrylate)/E7 polymer‐dispersed liquid crystal composites

Abstract

Experiments on the effect of temperature on the optical and electro-optical behaviors of polymer-dispersed liquid crystals (PDLCs) are considered. Composite films composed of poly(methyl methacrylate) (PMMA) and the nematic-type liquid crystal (LC) E7 were prepared by solvent casting in chloroform. The PDLC film contained droplets of E7 from 10 to 80 wt % in a PMMA matrix. Morphological studies illustrated the formation of isolated droplets of LC due to phase separation, and their homogeneous distribution increased with increasing E7 content. Thermo-optical studies showed an increase in the nematicisotropic transition temperature of composites, which indicated preferential solvation during the phase-separation process. The electro-optical characteristics were studied under the conditions of an externally applied square wave electric field with a He-Ne laser (k 5 632.8 nm) as a light source. The responses improved as the E7 content in PMMA increased. Semipermanent memory effects were noticed in composites at higher temperatures. Changes in the transmittance due to thermal variations provided the possibility of using such a device as a temperature sensor. The results obtained indicate that under these experimental conditions, the output can be controlled to the desired level by the selection of a suitable loading of LC to prepare PDLC electro-optically active composite films with a response time on the order of only a few milliseconds.

Dielectric relaxation and electro-optical switching behavior of nematic liquid crystal dispersed in poly(methyl methacrylate)

“…Hysteresis effect was also observed in other LC-polymer composite films prepared using SIPS technique [5,18,19]. Because in the SIPS technique, the morphology was highly influenced by the polymer/LC interaction, its viscosity and hence the distribution, shape and size of the droplets are different in the films prepared with different loading of LC in polymer matrix, which is clearly seen in SEM micrographs and optical polarizing images.…”

“…The graphs were plotted using the average of three sets of readings and subsequently the variation is reported in terms of an error bar in the figures. The detail of experimental setup for electro-optical measurement is given elsewhere [18,19].…”

Nematic–isotropic transition in polymer‐confined and polymer‐free liquid crystal mixtures

“…A nematic–isotropic phase transition 7 K higher than the clearing temperature of the pure LC mixture E7 has been found for E7/PMMA composites. This shift has been related to a preferential solvation of specific E7 constituents 16. The absence of such effects in composites prepared from poly(dimethylsiloxane) and single LC substances, for example, 4‐cyano‐4′‐ n ‐pentylbiphenyl or 4‐cyano‐4′‐ n ‐octylbiphenyl,11, 13 provides further evidence for an irregular separation in case of multicomponent LC phases.…”

Preparation and electro-optical characterization of aminosilane-modified silica gel dispersed liquid crystal films by the sol–gel process

“…One of the basic prerequisites for the employment of these PDLC cells is the uniform dispersion of liquid crystal droplets in polymer matrixes. The approaches to disperse liquid crystal droplets are mostly based on solvent induced phase separation, temperature induced phase separation and polymerization induced phase separation [4][5][6]. With these methods, however, it is difficult to mix three components (polymer monomer, hardener and UV light inducer) and may unavoidably cause different temperatures on the two sides of PDLC films.…”