Anionic surfactant adsorption on deep eutectic solvents

Deep Eutectic Solvents (DES) are molecular mixtures similar to ionic liquids, having melting points below room temperature. However instead of being a salt, the mixture contains two molecules with strong H-bonding that hinder formation of an ordered crystalline network. DES have low vapour pressure, adjustable polarity, and tunable components which make them interesting as green solvents while being far less toxic than typical ionic liquids. They are currently being extensively explored for extraction of active species from biomass and solubilisation of therapeutic agents for dermal delivery. These applications require formulation using DES in emulsions and gels, requiring surfactants to stabilise DES-oil or DES-water interfaces. While a few surfactants have been previously studied in DES, these have so far been restricted to model surfactants, and in the case of anionic surfactants this has been limited to species with sulphur containing headgroups. Here we wish to study the adsorption of anionic surfactants relevant to emulsification that have different headgroup chemistries, in adsorbed films at the air-DES interface to determine how they interact with DES and whether comparable interfacial structures are found to those formed on water.