Small-angle neutron scattering of Ca(AOT)2/D2O/decane microemulsions

Small-angle neutron scattering (SANS) studies were performed in order to investigate the structural properties of he monophasic domain of he Ca(AOT)(2)/water/decane phase diagram, which shows a consistent reduction of the microemulsion region as compared to the parent sodium system. Microemulsions of Ca(AOT)(2)/D2O/decane and Ca(AOT)(2)/H2O/decane-d(22) have been studied at 25 degrees C, for an oil dilution line at constant [water]/[Ca(AOT)(2)] = 25.1, as a function of decane concentration and of surfactant volume fraction, phi(S), in the range 0.0186 less than or equal to phi(S) < 0.0937 for the D2O system, or 0.0249 less than or equal to phi(S) less than or equal to 0.0886 for the corresponding decane-d(22) system. SANS spectra were analyzed according to a self-consistent method proposed by Sheu(1) and support, in analogy to the sodium AOT microemulsion system, the presence of polydisperse droplets in the diluted region studied, while the system shows a pecolative behavior for higher concentrations. These droplets have a 21.3 Angstrom average radius with polydispersity around 22%. The mean area per polar head group and the principal geometrical parameters are also reported.