Single particle and collective orientational relaxation in an anisotropic liquid near the isotropic-nematic transition

We report molecular dynamics simulation results for the single particle and collective orientational correlations for Gay-Berne fluid of anisotropy parameters kappa = 3 and kappa' = 5, The following significant results are reported. (i) The decay of collective orientational relaxation of rank two is found to slow down appreciably while approaching the isotropic-nematic (I-N) transition, It eventually becomes even slower than the single particle orientational relaxation of rank one. Surprisingly, even the latter shows a marked slowing down near the I-N transition. (ii) Analysis of the long-time behavior shows a breakdown of the rank dependence predicted by the Debye law in the same region. (iii) An analysis of the memory functions of the orientational time-correlation functions shows that for the collective relaxation surprisingly approaches a Markovian behavior near the I-N transition. (C) 1997 American Institute of Physics.