Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, Vol.368, 3837-3844, 2001
Electro-optical, spectroscopical, and calorimetric investigations of electron beam- and ultraviolet- cured polymer dispersed liquid crystal materials
The most convenient method used for the preparation of polymer dispersed liquid crystal (PDLC) films is the polymerization induced phase separation (PIPS) of mixtures composed of polymer precursors and low molecular weight liquid crystals (LMWLC). Ultraviolet (UV) and electron beam (EB) radiation was employed to initiate the PIPS process. A mixture of the nematic LMWLC material E7, an aromatic polyester acrylate, and additional monomeric acrylates was exposed to the EB radiation. Lucirin TPO as a photoinitiator has been included in the initial mixture in the case of UV exposure. The electro-optical properties of the obtained PDLC films strongly depend on the curing conditions, and are highly reproducible. In general it was found that the EB-cured PDLC films show a better electro-optical performance as compared to the UV-cured samples, The extent of cure has been determined by infrared spectroscopy measurements of the carbon-carbon double bond of the acrylate groups. Differential scanning calorimetry was employed to obtain the glass transition temperature of the polymer and the LMWLC solubility limit in the polymer matrix.