Nonexponential Behavior Near the Critical Point of an Ionic Micellar System

The coexistence curves of the system dodecylammonium chloride + water + KCl have been obtained for different salt concentrations. We found that the asymptotic behavior of the order parameter can be describe using extended scaling and the usual Ising value for the b = 0.325 exponent. The static light scattering data for the critical composition are also compatible with the Ising value v = 0.63. Dynamic light scattering results have been obtained near the liquid- liquid critical point. The correlation functions have been found to be single-exponential for temperatures well above critical, while a second decay process at longer times becomes evident for T— TC< 4K. These correlation functions can be fitted to the sum of two exponential functions. The diffusion coefficient associated with concentration fluctuations has been calculated from both relaxation modes. It has been analyzed in terms of the predictions of the mode-coupling theory. These results, together with correlation length and viscosity data, are in good agreement with the calculations.