SMALL-ANGLE SCATTERING APPLIED TO MICROEMULSIONS

We present a procedure for the evaluation of small-angle scattering da ta from microemulsions. A model independent picture of the structures in the various one-phase samples emerges from the Indirect Fourier Tra nsformation analysis of the measured small-angle neutron scattering (S ANS) spectra. The data analysis makes no a priori assumptions about th e 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 de nsity profile normal to the interface is obtained by a deconvolution t echnique. We have investigated the microstructures in the binary syste m water (D2O)/pentaethylene glycol monoperdeutero-n-dodecyl ether (C(1 2)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-a ngle neutron scattering. Spherical, cylindrical and planar morphologie s were induced by changing the temperature of samples with fixed compo sitions. The same structural sequence exists in both the binary and th e ternary mixtures. The spherical, cylindrical and planar structures a re observed for water-rich samples by increasing temperature. For oil- rich samples the same structural sequence occurs as function of decrea sing temperature. Both for water-rich and oil-rich samples, increasing the surfactant concentration at a constant ratio of surfactant to eit her oil or water, appropriately, causes the structures become more con centrated, but preserves the local structure and its dimensions.