COLLECTIVE AND SINGLE-PARTICLE DYNAMICS NEAR THE ISOTROPIC-NEMATIC PHASE-TRANSITION

We have studied the single-particle and the collective orientational d ynamics of a liquid crystal near the isotropic-nematic phase transitio n by performing time-resolved spectroscopy experiments. A compared ana lysis of results allows us to measure selectively the relaxation of si ngle-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 displ ays a biexponential decay with no critical phenomena. This experimenta l study suggests a possible general picture of the molecular dynamics, in which the local orientational order plays a leading role.