Transparent nematic phase in a liquid-crystal-based microemulsion

Complex fluids(1,2) are usually produced by mixing together several distinc t components, the interactions between which can give rise to unusual optic al and rheological properties of the system as a whole. For example, the pr operties of microemulsions (composed of water, oil and surfactants) are det ermined by the microscopic structural organization of the fluid that occurs owing to phase separation of the component elements. Here we investigate t he effect of introducing an additional organizing factor into such a fluid system, by replacing the oil component of a conventional water-in-oil micro emulsion with an intrinsically anisotropic fluid-a nematic liquid crystal. As with the conventional case, the fluid phase-separates into an emulsion o f water microdroplets (stabilized by the surfactant as inverse micelles) di spersed in the 'oil' phase. But the properties are further influenced by a significant directional coupling between the liquid-crystal molecules and t he surfactant tails that emerge (essentially radially) from the micelles. T he result is a modified bulk-liquid crystal that is an ordered nematic at t he mesoscopic level, but which does not exhibit the strong light scattering generally associated with bulk nematic order(2): the bulk material here is essentially isotropic and thus transparent.