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

Recent studies relate the slowing down of the structural relaxation time of supercooled liquids to a decrease of the excess entropy Sexc 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 Sexc and the configurational entropy Sc of the system. This work presents a direct test of the connection between dynamics and Sexc 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 Sexc to Sc is proposed. Finally, some comments on the dependence of the fragility on pressure are discussed.