Relaxation in supercooled liquids: A generalized hydrodynamic description

Abstract

We focus on the frequency dependence of the viscosity η(ω), or more specifically, of the retardational compliance Jr(ω), for supercooled liquids. We pursue a phenomenological approach which is related to extended hydrodynamics and is of a form compatible with a mode–mode coupling theory. While many of the transport coefficients entering the analysis are interrelated so as to give the correct temperature and frequency dependences of the observed quantities, an important consequence of the model is the prediction of nonArrhenius behavior for the Maxwell relaxation time τm. Our phenomenological approach suggests a mode coupling picture in which the bilinear modes are ‘‘semiconserved’’; in turn, the mode coupling analysis gives molecular insights into the empirical transport or relaxation coefficients.