Pressure and Temperature Dependence of Glass-Transition Dynamics in a “Fragile” Glass Former

A depolarized light-scattering study of isopropylbenzene has been carried out at pressures from 1 bar to 7.6 kbar and at temperatures from 293 to 122 K. Both the supercooled and superpressed liquids show two-step relaxation processes. The faster relaxation in both cases can be described by a mode-coupling $\beta$ relaxation theory. Comparison of the pressure and temperature data indicate that density is not the only relevant parameter required to explain the evolution of the $\beta$ relaxation dynamics as the liquid-glass transition is approached.