Small angle scattering applied to microemulsions

We present a procedure for the evaluation of small-angle scattering data from microemulsions. A model independent picture of the structures in the various one-phase samples emerges from the Indirect Fourier Transformation analysis of the measured small-angle neutron scattering (SANS) spectra. The data analysis makes no a priori assumptions about the type of structure. Rather, the pair distance distribution functions are so unique that an unambiguous assignment of spherical, cylindrical or planar geometry is possible. In addition, the scattering length density profile normal to the interface is obtained by a deconvolution technique. We have investigated the microstructures in the binary system water (D2O)/pentaethylene glycol monoperdeutero-n-dodecyl ether (C(12)D(25)E(5)) and in the ternary system (D2O)/pentaethylene glycol mono-n-dodecyl ether (C(12)E(5))/perdeuterated n-octane (C8D18) by small-angle neutron scattering. Spherical, cylindrical and planar morphologies were induced by changing the temperature of samples with fixed compositions. The same structural sequence exists in both the binary and the ternary mixtures. The spherical, cylindrical and planar structures are observed for water-rich samples by increasing temperature. For oil-rich samples the same structural sequence occurs as function of decreasing temperature. Both for water-rich and oil-rich samples, increasing the surfactant concentration at a constant ratio of surfactant to either oil or water, appropriately, causes the structures become more concentrated, but preserves the local structure and its dimensions.