Stochastic Dynamics in Near-Critical Supercritical Fluids

An extension of the generalized Langevin equation (GLE) is introduced in order to model diffusion processes in near-critical fluids. Unlike the standard GLE, this new approach allows a flexible description of the influence of slowly fluctuating local density distributions that occur in a fluid as its liquid−vapor critical point is approached. We find that, given an initial nonequilibrium ensemble, diffusion coefficients differing substantially from the expected bulk value can be observed at intermediate times, that is, at times longer than the velocity relaxation time but shorter than the local environment interconversion time.