A closed-form approximant is proposed for the dynamic scaling function that characterizes the behavior of the wave-number—dependent diffusion of the order-parameter fluctuations in a fluid near a critical point. The expression contains two parameters that determine the expected behavior of the diffusion coefficient in the hydrodynamic and in the nonlocal critical limits. The proposed scaling function yields an accurate representation of our recent experimental data for the 3-methylpentane and nitroethane mixture near the critical mixing point with parameter values that are in good agreement with the values predicted from theory.

• Received 16 March 1983

DOI:https://doi.org/10.1103/PhysRevA.28.1567