The curious case of surfactant self-assembly in H-bonding rich non-aqueous media: Unexpected effect of counterions

Deep eutectic solvents (DES) are considered a greener alternative to conventional ionic liquids, and their hydrogen bond-rich environment has been shown to support self-assembly of different amphiphiles. Here, we propose to perform a small angle neutron scattering (SANS) characterisation of the self-assembled nanostructures of STAC (cetrimonium chloride) and CTAB, cetrimonium bromide) in glycerol and DES glycelin (choline chloride:glycerol in a 1:2 molar ratio). Differing only in their counterions (Cl- vs Br-; Fig.1), the two surfactants exhibited, surprisingly, contrasting self-assembly behaviours: STAC formed a gel in glyceline but not in glyceol; whereas CTAB formed a gel in glycerol but not in glyceline (Fig. 2). SANS will provide unique nanostructural insights to complement rheology and polarised light microscopy, shedding light on the mechanisms of molecular self-assembly in such H-bonding rich non-aqueous media, important to their future application as a green solvent.