Anomalous rotational diffusion in the vicinity of the isotropic to nematic phase transition

Abstract

Dielectric relaxation measurements are performed with very high accuracy on a liquid crystalline compound n-octylcyanobiphenyl (8CB) in the isotropic (I), nematic (N) and smectic A (SA) phases. The data obtained display an essential difference in the rotational diffusion process in the vicinity of the I–N phase transition in comparison to that taking place in the vicinity of the N–SA phase transition. Thus, for the I–N transition, anomalously slow diffusion (subdiffusion), characterized by an anomalous coefficient α<1, is observed, while normal Brownian rotational diffusion with is found for the N–SA transition. It is also shown how the fractal parameter α is temperature dependent with an extremely sharp variation at the I–N transition point in the form of a lambda-like profile.