Stokes-Einstein diffusion of critical fluctuations in a fluid

Abstract

The diffusion coefficient associated with the order-parameter fluctuations near the critical point of fluids is expected to vanish asymptotically as D=RkT6πηξ, where η is the viscosity, ξ the correlation length, and R a universal constant. Our experiments, using 3-methylpentane-nitroethane, yield R=1.02±0.06, in agreement with the mode-coupling theory of critical fluctuations, but in disagreement with the value R6π=1.26π≃15π, recently suggested by several investigators.