Interactions of water and amphiphiles with deep eutectic solvent nanostructures

Deep eutectic solvents (DES) are extensively hydrogen-bonded eutectic mixtures with low melting points. The presence of H-bonding makes them highly susceptible to interactions with water and also allows them to support amphiphile self-assembly, both for surfactants and biological lipids. Water disrupts the DES nework through intermolecular H-bonding, leading to changes in physicochemical properties: melting point, density and viscosity decrease; whereas electrical conductivity increases as water is added. Trends in these properties and structural studies suggest an upper hydration limit, where a transition is observed, around 60-80mol% water, from water-in-DES to DES-in-water behavior. Amphiphiles form aggregates in DES depending on solvophobicity, water content and Gordon parameter with structures ranging from globular micelles to highly ordered hexagonal/cubic phases. Lipid vesicle formation is also observed in DES with and without water. These interactions find important applications in fields such as biology, nanoparticle synthesis and electrodeposition.