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/NlaCl - 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 L-3 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. (C) 2021 Elsevier Inc. All rights reserved.