A New Type of Supramolecular Fluid Based on H₂O-Alkylammonium/Phosphonium Solutions

Here we show that by adjusting the concentration of tetrabutyl ammonium and phosphonium salts in water (approximate to 1.5-2.0 m), hydrophobic solvation triggers the formation of a unique, highly incompressible supramolecular liquid, with a dynamic structure similar to clathrates, involving essentially all H₂O molecules of the solvent. Despite the increasing local order, the thermal diffusivity, and compressibility of these supramolecular liquids is strongly decreased with respect to bulk water due to slower relaxation dynamics. The results presented in this paper open an avenue to design a new family of supramolecular fluids, stable under atmospheric conditions, which can find important technological applications in energy storage and conversion.