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

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 < 1, is observed, while normal Brownian rotational diffusion with &alpha approx 1; is found for the N-SA transition. It is also shown how the fractal parameter is temperature dependent with an extremely sharp variation at the I-N transition point in the form of a lambda-like profile.