Glass-like relaxation in confined liquid crystals

We have investigated the dynamics of reorientations of molecules due to their rotation around short axes and dynamics of director fluctuations (collective mode) in 5CB confined in porous matrices with randomly oriented, interconnected pores of average size 100 Angstrom. The confinement strongly influences the dynamics of molecular and collective modes and has resulted in qualitative 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 supercooled state is slower than at the temperatures corresponding to nematic phase by many orders of magnitude. This slowing down is accompanied by anomalous broadening of the spectra. The temperature dependencies of relaxation times of both processes obey the Vogel-Fulcher law suggesting that confined 5CB has dynamic features typical for glass-like behavior although in bulk it is a non glass former.