Aggregation behaviour of cationic surfactants in the imidazolium-based deep eutectic solvent

Deep eutectic solvents (DESs) have received significant attention as the solvent media for the self-assembly of amphiphiles over the past decade. However, the role of the hydrogen bond acceptor (HBA) identity in controlling aggregation remains unexplored. In this work, we report the aggregation behaviour of cationic imidazolium surfactants CnmimBr (n = 12, 14, 16) in an imidazolium-based DES (E1EG2), composed of 1-ethyl-3-methyl-imidazolium chloride and ethyl glycol. The structures and properties of various aggregates, including micelles and diverse lyotropic liquid crystals (LLCs), were characterised by polarised optical microscopy, small angle X-ray scattering and rheology. As the alkyl chain length increases, more elongated micelles and less curved LLCs are formed. Benefiting from their relatively high conductivity, these LLCs show promising potential as gel electrolytes. Compared with the conventional DES composed of choline chloride and ethyl glycol (ChEG), the surfactant adopts a smaller critical packing parameter in E1EG2. This work reveals that tuning the HBA provides a powerful strategy to control surfactant packing and phase behaviour in DES, expanding the application of ordered molecular aggregates.