Rough surfaces for orientation control in reverse mode polymer dispersed liquid crystal films

Reverse mode operation shutters have been achieved with polymer dispersed l iquid crystals by means of polymerization-induced phase separation of nemat ic mixtures consisting of a low molecular mass liquid crystal and a liquid crystalline monomer. Fluid mixtures were homeotropically aligned by rough s urfaces and transparent films were obtained after polymerization. Transmitt ance in the OFF state can be larger than 80% and decreases to less than 1% when an electric held of about 2 V mu m(-1) at 1 kHz is applied (ON state). Both rise and decay times can be lower than 10 ms and the drop in the OFF state normal transmittance is drastically reduced with respect to conventio nal polymer dispersed liquid crystals since samples exhibit a reverse morph ology. The role played by surface roughness is also discussed.