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 S-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-exc and the configurational entropy S-c of the system. This work presents a direct test of the connection between dynamics and S-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-exc to S-c is proposed. Finally, some comments on the dependence of the fragility on pressure are discussed.