Collective and single-particle dynamics near the isotropic-nematic phase transition

We have studied the single-particle and the collective orientational dynamics of a liquid crystal near the isotropic-nematic phase transition by performing time-resolved spectroscopy experiments. A compared analysis of results allows us to measure selectively the relaxation of single-and pair-particle time-dependent correlation functions. The pair-particle correlation relaxes with a slow monoexponential decay showing strong pre-transitional effects. The single-particle relaxation displays a biexponential decay with no critical phenomena. This experimental study suggests a possible general picture of the molecular dynamics, in which the local orientational order plays a leading role.