Relaxation Behaviour of Monomer/Liquid Crystal Blends after Exposure to Ultraviolet Light

Polymer Dispersed Liquid Crystal materials were elaborated by in situ polymerization induced phase separation under ultraviolet (UV) radiation. Binary model systems composed of a diacrylate monomer and a liquid crystal (LC), 4-cyano-4'-n-pentyl-biphenyl (5CB), were used as starting materials in the process of polymerization/crosslinking. The optical transmission of the monomer/LC films was monitored as function of time covering the period of exposure to UV-light and the following relaxation processes of the irradiated samples. The off-state transmission shows several characteristic processes, a short time relaxation process which decays within seconds, an unexpected intermediate period where transmission was found to enhance, followed by a long lasting relaxation process which takes tens of minutes to decay completely. A discussion of these processes in terms of the kinetics of phase separation is presented.