Static and dynamic light scattering studies of water‐in‐oil microemulsions in the critical region. Evidence of a crossover effect

Extensive light scattering measurements, including the intensity, turbidity, and linewidth, on a three‐component microemulsion system consisting of mixtures of water, decane, and a surfactant sodium di‐2 ethylhexylsulfosuccinate (AOT) (WDA), have been made. The critical and several off‐critical mixtures have been studied along constant microemulsion droplet volume fraction lines in the one‐phase region over a very large temperature range. In the vicinity of the lower phase separation temperature Tp the intensity data are very well accounted for by the standard theory of critical binary fluids using a single value for the short range correlation length ξ0=(13.5±1.5) A. By combining a mode‐coupling theory including the background effects and a linear model equation of state applicable in the critical region, we have been able to fit the dynamic light scattering data using a Debye cutoff length q−1D which is equal to the constant average diameter of microemulsion droplets. Furthermore, we find clear evidence...