VISCOSITY OF DROPLET-PHASE WATER AOT/ISOOCTANE MICROEMULSIONS - SOLIDSPHERE BEHAVIOR AND AGGREGATION/

We have measured the viscosity of water/AOT/isooctane microemulsions a s a function of the droplet volume fraction at different temperatures for two values of the molar water to surfactant ratio w0:25 and 35. Fr om the data we conclude that the microemulsion droplets behave like so lid spheres, since (1) the low volume fraction dependence of the relat ive viscosity follows Einstein's relation and (2) at sufficiently low temperatures the coefficients of the second- and third-order terms in the volume fraction expansion of the relative viscosity equal those fo und for latex and silica spheres. Furthermore, we find that the drople ts aggregate reversibly at the higher temperatures. The enthalpies of binding of the observed clustering process were found to be 89 and 121 kJ/mol for w0 = 25 and 35, respectively, which is in good agreement w ith dielectric permittivity measurements on the same system.