Pre-transitional effects in the liquid-plastic phase transition of p-terphenyl

A study of the orientational dynamics of liquid p-terphenyl in the time domain by means of transient optical Kerr effect spectroscopy is presented. The orientational relaxation is measured at several temperatures above the liquid-plastic phase transition, following the decay from a few hundreds of fs to about 700 ps. Pre-transitional effects are observed above the phase transition. Approaching the transition temperature, a bifurcation of the orientational relaxation times is present. The faster orientational time follows the Debye-Stokes-Einstein hydrodynamic theory up to the phase transition without any critical effect. The slower time shows a typical critical slowing down, in agreement with the Landau-de Gennes theory of first-order phase transitions.