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 li quid crystal (PDLC) films is the polymerization induced phase separation (P IPS) of mixtures composed of polymer precursors and low molecular weight li quid crystals (LMWLC). Ultraviolet (UV) and electron beam (EB) radiation wa s employed to initiate the PIPS process. A mixture of the nematic LMWLC mat erial E7, an aromatic polyester acrylate, and additional monomeric acrylate s 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-op tical properties of the obtained PDLC films strongly depend on the curing c onditions, 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 sp ectroscopy measurements of the carbon-carbon double bond of the acrylate gr oups. Differential scanning calorimetry was employed to obtain the glass tr ansition temperature of the polymer and the LMWLC solubility limit in the p olymer matrix.