Electric Field Effect on the Critical Opalescence. II. Relaxation Times of Concentration Fluctuations

Abstract
In an investigation of the effect of electric fields on the critical opalescence, time‐dependent phenomena have been observed which are related to theoretical relaxation times of concentration fluctuations for a binary mixture. Rectangular dc pulses of 25 to 60 kV/cm and 10–200‐μsec duration have been applied to a critical mixture nitrobenzene and 2,2,4‐trimethylpentane at a series of temperatures above the critical solution temperature. Relaxation times associated with the change in the transmitted light intensity were found to be independent of the pulse width and the field strength. The relaxation times are proportional to (T—Tc)−0.9 and have magnitudes comparable with relaxation times determined from the frequency broadening of light scattered from similar binary systems. It has also been possible to extend the agreement between the Debye theory of the electric field effect on critical opalescence and the experimental results to within 0.1°C of the critical temperature.