Electro-optical characterization of E48:PVP polymer dispersed liquid crystals

Transmittance behavior of nematic E48:polyvinylpyrrolidone (PVP) polymer dispersed liquid crystals (PDLC) is investigated in relation to the liquid crystals to polymer ratio. Five E48:PVP concentration mixtures are prepared: 75:25, 77.5:22.5, 80:20, 82.5:17.5, and 85:15. Solvent Induced Phase Separation and Thermally Induced Phase Separation techniques are used. Droplet sizes are measured using a polarizing microscope, and the 80:20 mixture prepared by slow cooling is determined to have the largest droplets. The liquid crystal cells prepared by fast cooling needed a higher switching voltage (ranging from 7V-35V) while the switching voltage of slow-cooled samples varied from 6V-47V, with most of the samples having switching voltages close to 10V. The transmittance behavior and contrast ratio of PDLC's are then investigated with a 660-680 nm light source. It is observed that fast-cooled samples had higher contrast ratios compared to slow cooled samples. Photographs of each sample are acquired to determine their respective textures.