Structure in microemulsions of di-chained surfactants

Small-angle neutron scattering (SANS) is used to probe structure in water-in-oil microemulsions containing n-alkyl-n-dodecyldimethylammonium bromides [R(1)(C12H25)N(CH3)(2)Br-+(-)], with R(1)-n-C-10, n-C-14, n-C-16 and n-C-18. The data from a core-shell-drop contrast series at the solubilisation phase boundary are analysed using a model that is sensitive to the surfactant film composition. The results suggest that there is a small amount of cyclohexane penetration into the negatively curved monolayer. For example with the n-C-18 surfactant, the volume fraction of C6D12 in the film is ca. 0.08.