Thermal and Nonlinear Optical Properties of Potassium Laurate/Water Solutions at Amphiphilic Concentrations around the Critical Micellar Concentration: A Laser Gaussian Single Beam Experiment in Millisecond Timescales

Abstract

The thermooptic coefficient, thermal conductivity κ, and nonlinear index of refraction of the mixture of potassium laurate and water, around the critical micellar concentration (cmc), are measured as a function of the amphiphile concentration, using the Z-Scan technique in a millisecond time scale. In this time scale, during which the sample is exposed to the laser beam, heat diffusion takes place and, in the same time, the thermodiffusion process is not present. Our results indicate that the presence of micelles in the solution, in a concentration domain up to 100 × cmc, does not significantly modify the thermal conductivity of the solution, with respect to the value of κ in the solution of isolated amphiphilic molecules. On the other hand, the presence of micelles in the solution modifies the thermooptic coefficient and the nonlinear index of refraction behaviors as a function of the amphiphilic concentration (c). When this result is compared with the behavior of the electrical conductivities of the amphiphilic solutions as a function of c, the ion mobility in the system seems to be related to the nonlinear response of the medium.