Configurational and excess entropy in a fragile glass former and their relation with structural relaxation

A method to derive experimentally the configurational entropy that governs the structural relaxation process in supercooled (supercompressed) liquids is presented. Light scattering, dielectric, calorimetric and dilatometric measurements are used to test the method in o-terphenyl. The combined analysis of relaxation data as a function of temperature and pressure is found to be essential to quantify a realistic value of the non-structural thermal expansion and the configurational entropy of the system. The latter is estimated as a fraction of the excess entropy of the liquid over its stable crystalline phase. Our results indicate that the number of configurations connected to the structural relaxation contributes approximately 70% to the excess entropy.