This proposal concerns a novel approach to phase separation in self-assembling colloidal systems. Microemulsions can be readily formulated to display critical-type phase separation, resulting into two coexisting fluids of different densities (Fig. 1a) above a characteristic critical temperature (Tc). Recent studies have shown that polymer added to critical microemulsions can significantly depress Tc, whilst retaining a clean bi-phasic separation (Fig. 1a). Contrast variation SANS (CV-SANS) studies of these interesting multi-component systems are proposed to investigate the effects of added polymer on the underlying structure, in order to better understand the phase behaviour properties. These new observations of polymer-induced transitions may help in the search for low-energy separation processes requiring lower heat consumption, and also recovery of high value solutes such as proteins.