Heat Capacity and Entropy Functions in Strong and Fragile Glass-Formers, Relative to Those of Disordering Crystalline Materials

Abstract

A review considers the highly variable forms that the heat capacities of glassforming liqs. can take, and will then show that, in spite of this great variation, the integrals of the heat capacities, the entropies, S = ∫CpdT - and particularly its excess over the entropy due to vibrations - fall into a pattern that mimics the well-known pattern made by the viscosities of glassformers when plotted in Tg-scaled Arrhenius form (the 'strong/fragile' liq. pattern). While the origin of the 'strong/fragile' pattern for viscosities (and relaxation times) remains more or less mysterious, the pattern for the entropies can be simply reproduced using a two-parameter model of configurational excitations , as will be demonstrated. It also interprets the 'strong liq.' extreme of this pattern in a provocative way by showing the similarity that the heat capacity function for these liqs. bears to a well-known heat capacity form for disordering excitations in solids, the lambda transition. [on SciFinder(R)]