Correlation between configurational entropy and structural relaxation time in glass-forming liquids

Abstract

Recent studies relate the slowing down of the structural relaxation time of supercooled liquids to a decrease of the excess entropy ${S}_{\mathrm{exc}}$ of the melt with respect to the crystal. The theoretical basis of such a result was often found in the Adam Gibbs (AG) theory, implicitly assuming a proportionality between ${S}_{\mathrm{exc}}$ and the configurational entropy ${S}_{c}$ of the system. This work presents a direct test of the connection between dynamics and ${S}_{\mathrm{exc}}$ over a wide temperature and pressure interval for three different glass forming systems, o-terphenyl, triphenylchloromethane, and poly(methylmethacrylate). Moreover, a method, based on the AG theory, to estimate the isothermal and the isobaric contribution of ${S}_{\mathrm{exc}}$ to ${S}_{c}$ is proposed. Finally, some comments on the dependence of the fragility on pressure are discussed.