Frequency-Dependent Bulk Viscosity in One- And Two-Component Near-Critical Fluids

We assume isomorphism between near-critical fluids and Ising spin systems to calculate the critical anomaly of transport coefficients. As an example we present a very simple and general expression for the frequency-dependent bulk viscosity f * ( y ) in one- and two-component fluids near the critical point. It reads f *((y) = p(c2 — c2) f(iw/ri)/iW, where f ( z ) is a universal complex function, c is the zero-frequency sound velocity, cc is its critical value, and re is the order parameter relaxation rate. We also examine macroscopic adiabatic relaxations of pressure, temperature, and density after stepwise changes of pressure or density. Such measurements give information on the time correlation function of the diagonal part of the stress, which relaxes anomalously slowly near the critical point.