Dielectric relaxation in liquid crystals confined in a quasi-one-dimensional system

Dielectric spectroscopy was used to investigate the influence of confinement of the liquid crystal 4-n-penyl-4′-cyanobiphenyl 5CB (LC) on the nematic-to-isotropic (N–I) phase transition and the dynamics of molecular reorientations via rotation of molecules around their short axis under extremely narrow confinement in pores of 2.3 nm diameter, that may be considered a quasi-one-dimensional (1D) system. We observed that, instead of undergoing the N–I phase transition in the quasi-1D system, 5CB inside the 2.3 nm pores shows dynamic behavior typical for supercooled liquids. Relaxation of molecular origin dramatically slows down upon cooling the sample from the isotropic phase. Molecular reorientations were dielectrically active at temperatures much above the bulk N–I transition temperature but with the relaxation rate much slower and dielectric spectrum much broader than in the bulk 5CB. We suggest that the slowing down of the mode, which is molecular in the bulk material, may be due to enhancement of the effective viscosity of 5CB under such narrow confinement, resulting in supercooled dynamics.