The aim of this proposal is to investigate a novel approach to phase separation in microemulsions using careful choice of organic solvents, and appropriate mixtures. Microemulsions can display a very specific phase separation into two coexisting fluids of different densities above a characteristic critical temperature (Tcrit) [1]; at other temperatures a cloud-point separation of a water-rich phase (Tcloud) is more commonly observed [2]. Recent studies have shown that changing hydrocarbon solvent quality, through formulation of well-defined alkane mixtures, depresses Tcrit, whilst also retaining a clean bi-phasic separation. The aim of this proposal is to conduct the first detailed contrast variation small-angle neutron scattering (CV ¿ SANS) structural study of microemulsions phase separated by variations in mixed solvent composition (quality), above and below both Tcrit and Tcloud.