A light scattering study on the droplet size and interdroplet interaction in microemulsions of AOT—oil—water system

Abstract Quasi-elastic light scattering and static light scattering techniques were used to study the droplet size and interdroplet interaction in W/O microemulsions consisting of AOT, oil, and water. The intrinsic diffusion coefficients and the virial coefficients were determined by extrapolating the experimental data to infinite dilution and studied as functions of the following variables: the molar ratio of water to surfactants, the chain length of oil, salinity, and the ratio of nonionic surfactant, Arlacel-20, to AOT. Time-averaged intensity data were interpreted based on the theory of hard sphere model with a small perturbation due to attractive interaction between the spheres. It was found that the droplet size and the interdroplet attractive interaction increased with the molar ratio of water to AOT and the chain length of oil. In contrast, an increase in salinity decreased the droplet size and interdroplet attractive interaction. The addition of Arlacel-20 increased the droplet sized but decreased the strength of the attractive interaction between microemulsion droplets. In addition to the dilution procedure, the angle-dependent measurements were also made and the data were analyzed by a square well attractive potential. It is emphasized that one must be cautious of the inaccuracy of angle-dependent analysis, since the dependence of diffusion coefficients on angle on microemulsions is usually very weak and within the experimental error.