Alternative non-aqueous water-miscible solvents for surfactants

Adsorption and aggregation properties of model non-ionic CiE8 surfactants (octaethyleneoxide mono-n-alkyl ethers C12E8, C14E8 and C16E8) were studied in different solvents: water, water/ethylene glycol and water/propylene glycol mixtures, as well as pure ethylene and propylene glycol. Significant changes in critical micellar concentrations, surface tensions and surface excess were observed using surface tension, as a function of solvent type and surfactant tail length. Aggregation structures in these solvents were studied using small-angle neutron scattering (SANS). The SANS results were consistent with ellipsoidal, or cylindrical micelles, depending on solvent. Importantly, pure ethylene glycol is identified as a solvent in which CiE8 surfactants exhibit classic behavior, similar to that which has been well documented in water. On the other hand, C12E8 exhibits only very weak surfactant properties in pure propylene glycol: surface tension depressions were very small, and SANS signals were weak, suggesting only minimal adsorption and aggregation. Hence, surfactant behavior of a model non-ionic like C12E8 is strongly dependent on the type of glycol.