Time dependence of critical concentration fluctuations in a binary liquid

Accurate measurements of the time dependence of the order-parameter fluctuations in the binary liquid mixture 3-methylpentane and nitroethane very close to the critical temperature are reported. The experiments were performed by cross correlating the scattered light received by two different photomultiplier tubes to eliminate distortions of the observed correlation function due to afterpulsing. The measurements reveal the presence of small but noticeable deviations from exponential decay of the critical concentration fluctuations. The observed phenomenon can be attributed to the effect of a frequency-dependent critical viscosity as predicted by Ferrell and co-workers.