Effect of temperature and volume on structural relaxation time: Interpretation in terms of decrease of configurational entropy

We analyze the slowing down of structural relaxation dynamics of two small molecular glass formers and one polymer: o-terphenyl, triphenylchloromethane, and poly(methylmethacrylate). Considering the literature data of expansivity and heat capacity we calculate configurational entropy using a previously proposed relation between the configurational and the excess entropy, and we directly check the Adam and Gibbs theory for glass transition. In particular, we clearly show that using such expression for configurational entropy the predicted linear dependence between the logarithmic of structural relaxation time and the product of temperature with configurational entropy is well satisfied and it does not depend on pressure. Moreover, we also derive an equation for calculating the pressure dependence of the glass transition temperature, which in these systems is in good accordance with the experimental values. (c) 2005 Elsevier B.V. All rights reserved.