Dynamically correlated regions and configurational entropy in supercooled liquids

When a liquid is cooled below its melting temperature, if crystallization is avoided, it forms a glass. Thisphenomenon, called glass transition, is characterized by a marked increase of viscosity, about 14 orders ofmagnitude, in a narrow temperature interval. The microscopic mechanism behind the glass transition is stillpoorly understood. However, recently, great advances have been made in the identification of cooperatiVerearranging regions, or dynamical heterogeneities, i.e., domains of the liquid whose relaxation is highlycorrelated. The growth of the size of these domains is now believed to be the driving mechanism for theincrease of the viscosity. Recently a tool to quantify the size of these domains has been proposed. We applythis tool to a wide class of materials to investigate the correlation between the size of the heterogeneities andtheir configurational entropy, i.e., the number of states accessible to a correlated domain. We find that therelaxation time of a given system, apart from a material dependent prefactor, is a uniVersal function of theconfigurational entropy of a correlated domain. As a consequence, we find that, at the glass transitiontemperature, the size of the domains and the configurational entropy per unit volume are anticorrelated, asoriginally predicted by the Adam-Gibbs theory. Finally, we use our data to extract some exponents definedin the framework of the random first-order theory, a recent quantitative theory of the glass transition.