Stable 'soap and water' sponges doped with metal nanoparticles

This paper presents various aspects of surfactant/oil/water L-3 phases. Although these so-called 'sponge phases' are usually stable only within a narrow temperature range, we show here that they can be stabilized over a larger phase space by doping with metal nanoparticle suspensions. We make and study sponge-phase samples doped with Au, Ag, and Pd aquasols and organosols. Remarkably, Pd-doped sponge phases are stable up to temperatures as high as 50 degrees C. Polarised microscopy studies as well as small-angle X-ray scattering measurements (SAXS) confirm that the nanoparticles are indeed incorporated in the sponge phase membrane. Moreover, rheological measurements show that, unlike the undoped samples, metal-doped sponge phases exhibit reversible phase transitions under shear stress. The various factors that control the stability and special optical properties of these metal-doped sponge phases are outlined and discussed.