The effect of cluster dynamics on the α-relaxation in supercooled liquids

The dielectric relaxation in a supercooled liquid is analyzed in a model in which the liquid is composed of slowly moving molecules within clusters and fast ones between them. If the dielectric α-relaxation of molecules inside a cluster is described by a stretched exponential function then the cluster dynamics, with molecules leaving and entering the clusters, can lead to the relaxation of the system’s polarization being described by a stretched exponential function with a larger stretching exponent, that depends on the rate at which the molecules leave the clusters. The implications of this for time–temperature superposition and other properties of supercooled liquids are discussed.