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

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 nematic–isotropic 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 (λ = 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.