VISCOSITY, MICROSTRUCTURE, AND INTERPARTICLE POTENTIAL OF AOT H2O/N-DECANE INVERSE MICROEMULSIONS/

Single-phase AOT/H2O/n-decane inverse microemulsions have been studied by using capillary viscometry and small-angle neutron scattering (SAN S). This ternary mixture is treated as a polydisperse colloidal suspen sion, where the established overlap potential for the droplet interact ion is approximated by a square-well interaction. Viscosity measuremen ts on both dilute and concentrated microemulsions show an anomalous ma ximum with increased swelling of the droplets. Predictions for the dil ute viscosity from the effective interaction parameters extracted from the microemulsion structures measured by SANS also show a maximum wit h swelling, but of a smaller magnitude. The viscometry and the SANS me asurements are combined to extract the interparticle potential. Compar ison shows, however, that two different sets of interaction parameters are extracted, a consequence of the approximate nature of the square- well colloidal model. A molecular mechanism is proposed to explain the viscosity anomaly, whereby disorder at the surfactant/water interface leads to increased overlap and, hence, stronger effective interaction s. The results are discussed within the context of earlier work on the percolation transition in these inverse microemulsion systems.