Effect of dichroic dye on phase separation kinetics and electro-optical characteristics of polymer dispersed liquid crystals

Dichroic polymer dispersed liquid crystal (PDLC) films were prepared using a nematic liquid crystal, photo-curable polymer and dichroic azo dye by polymerization induced phase separation (PIPS) method. Dynamics of PIPS and morphology development in the mixtures containing dye have been investigated by means of UV-VIS spectroscopy and optical microscopy. The phase separation and segregation of LC droplets was found to be dependent on the amount of dye used. LC droplets predominantly exhibited bipolar configuration that changed to maltese type crosses under the influence of an applied electric field. The extent of interaction and anchoring energy between the LC and polymer were examined by measuring contact angle in consequence of dye addition. Due to less interfacial interaction. PDLC with low dye content (<= 0.06 wt%) gave a good contrast ratio, relatively low threshold voltage and a value of high transmittance in the ON-state. UV-VIS spectroscopy results show that the molecular orientation of dye in LC droplets can be controlled with an applied field to induce nonlinearity in these materials. In particular, the dye concentration can be optimized to obtain promising electronic materials with minimum threshold and high contrast for display applications. (C) 2012 Elsevier Ltd. All rights reserved.