Experimental evidence of a transition from a sponge-like to a foam-like nanostructure in water-rich L3 phases

Hypothesis The micrometer-sized gas bubbles of a liquid foam with a dispersed gas phase of > 74 vol% are polyhedral and surrounded by a continuous aqueous phase. The structure of a water-rich microemulsion with a water phase of > 74 vol% normally consists of oil droplets in water or is bicontinuous. We hypothesize that at these high water contents polyhedral water droplets in oil can also exist. Experiments We (a) carried out phase studies on the water-rich side of the phase diagram of the quaternary system water/NaCl – hexyl methacrylate – AOT, because AOT is known for its propensity to form water-in-oil structures and hexyl methacrylate can be polymerized, (b) measured the electrical conductivities and viscosities, and (c) visualized the nanostructure with freeze-fracture electron microscopy (FFEM). Findings We found narrow 1-phase regions emanating from the L3 phase of the oil-free water/NaCl – AOT system by adding small amounts of oil. In these regions the conductivities become extremely low and the viscosities are extremely high. In addition, FFEM images clearly show the foam-like nanostructure.