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 reduc tion of the microemulsion region as compared to the parent sodium syst em. 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 c onstant [water]/[Ca(AOT)(2)] = 25.1, as a function of decane concentra tion and of surfactant volume fraction, phi(S), in the range 0.0186 le ss 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 correspo nding decane-d(22) system. SANS spectra were analyzed according to a s elf-consistent method proposed by Sheu(1) and support, in analogy to t he sodium AOT microemulsion system, the presence of polydisperse dropl ets in the diluted region studied, while the system shows a pecolative behavior for higher concentrations. These droplets have a 21.3 Angstr om average radius with polydispersity around 22%. The mean area per po lar head group and the principal geometrical parameters are also repor ted.