Glass-like relaxation in confined liquid crystals

We have investigated the dynamics of reorientations of molecules due to the ir rotation around short axes and dynamics of director fluctuations (collec tive mode) in 5CB confined in porous matrices with randomly oriented, inter connected pores of average size 100 Angstrom. The confinement strongly infl uences the dynamics of molecular and collective modes and has resulted in q ualitative changes in 5CB properties. Deep supercooling of 5CB in pores up to 150 degrees below the bulk crystallization temperature was observed. The relaxation rate of the process due to the molecular rotation in deeply sup ercooled state is slower than at the temperatures corresponding to nematic phase by many orders of magnitude. This slowing down is accompanied by anom alous broadening of the spectra. The temperature dependencies of relaxation times of both processes obey the Vogel-Fulcher law suggesting that confine d 5CB has dynamic features typical for glass-like behavior although in bulk it is a non glass former.