Inhomogeneities and relaxation in supercooled liquids

摘要

Nonexponential relaxation in glass forming liquids has been attributed by Robertson and Donth to inhomogeneous distribution of small local regions. We show, based neither on freehyphen;volume nor on configurational entropy theories that the correlation volumeVof such inhomogeneous regions isR lsqb;Dgr;Hast; (1minus;x)/RTrsqb;2lcub;kBT4gDgr;kgr;Tg/lang; Dgr;2thinsp;lnthinsp;tgr;rang;rcub;, where Dgr;hast; is the enthalpy of activation near the glass transition temperatureTg,xis the Narayanaswamyndash;Gardon nonlinear parameter, Dgr;kgr;Tgis the change in thermal conductivity atTg, lang;Dgr;2thinsp;lnthinsp;tgr;rang;, describes how wide is the spectrum of relaxation times, andkBandRare the Boltzmann and the gas constants, respectively. The correlation length does not diverge atTg. In fact, the correlation length atTgfor B2O3, glycerol, and PVAc are found to be approximately 1.27, 0.91, and 1.53 nm, respectively. Our results indicate, in agreement with Moynihan and Schroeder, that characteristics of nonexponential relaxation in glass forming liquids may be due to inhomogeneous domains whose size are in the nanometer length scale.