Evidence of Mode-Mode Coupling and Nonlocal Shear Viscosity in a Binary Mixture near the Consolute Point

Linewidths of Rayleigh scattering from a binary liquid system of $n-\mathrm{h}\mathrm{e}\mathrm{x}\mathrm{a}\mathrm{n}\mathrm{e}\mathrm{p}\mathrm{l}\mathrm{u}\mathrm{s}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{r}\mathrm{o}\mathrm{b}\mathrm{e}\mathrm{n}\mathrm{z}\mathrm{e}\mathrm{n}\mathrm{e}$ have been measured at two fixed scattering angles over a temperature range such that $\epsilon \equiv \frac{(T-T_c)}{T_c}$ extends from ${10}^{-2\mathrm{}}$ to ${10}^{-6\mathrm{}}$. The ratio of the linewidths at two angles as a function of the correlation length $\xi$ have been compared with recent self-consistent mode-mode coupling calculations of Kawasaki and Lo. The theory takes into account the nonlocality of shear viscosity near the critical point, and the data clearly establish the predicted effect in the critical region.