Dynamics of librational mode of nematic liquid crystal confined in cylindrical pores

Dielectric spectroscopy was applied to investigate the dynamic properties o f nematic liquid crystal - 5CB confined in 2000 cylindrical pores of Anopor e membranes with the molecules oriented perpendicular to the pore wall with lecithin treated surface. This allows the investigation of the librational (tumbling) mode since the probing electric field is parallel to the pore a xis. We found that the dynamics of the librational mode is totally differen t from the behavior observed in investigations of relaxation due to reorien tation of molecules around their short axis. The interpretation of the temp erature dependence of relaxation times in nematic phase needs the involveme nt of the temperature dependence of orientational order parameter. In the s upercooled state, the temperature dependence of the librational mode did no t follow the behavior observed in the nematic phase and shows a sharp incre ase while the temperature is decreased that is mainly determined by the var iations of viscosity.