Influence of local liquid structure on orientational dynamics: isotropic phase of liquid crystals

Measurements of orientational relaxation over 6 decades in time (femtoseconds to nanoseconds) and 10 decades of amplitude are reported for the liquid crystal N-(methoxybenzylidene)butylaniline (MBBA) in its isotropic phase. The measurements were made using the transient grating optical Kerr effect method. The faster dynamics (picoseconds to nanoseconds) display a power law decay that is temperature independent up to 43 deg above the nematic-isotropic phase transition. The slower dynamics (tens of nanoseconds) obey the Landau-de Gennes (LdG) modified Debye-Stokes-Einstein hydrodynamic equation. The faster dynamics become temperature dependent at the same temperature that the slower dynamics begin to deviate from LdG behavior