Mixed micellar solutions of an oleo-furan sulfonate surfactant with anionic and non-ionic surfactants

Small angle neutron scattering (SANS) has been employed to examine the self-assembly behaviour of sodium 5-tetradecyl furan-2-sulfonate (STFS), an emerging anionic surfactant, in bulk dilute solutions. STFS was also studied in binary and ternary mixtures with a common non-ionic (hexaethylene glycol monododecyl ether, C₁₂E₆) and anionic (sodium dodecyl sulfate, SDS) surfactant to explore the shape, size and composition of the mixed systems in dilute solution. SANS confirmed that STFS alone formed prolate ellipsoidal micelles and transitioned to small polydisperse spherical core-shell micelles of 55 ± 5 Å diameter for mixed systems. Anionic/non-ionic STFS/C₁₂E₆ mixtures exhibited strong synergistic interactions, with a significant reduction in critical micelle concentration (CMC) and preferential incorporation of C₁₂E₆ into the micelle compared to bulk solution molar ratios. In contrast, STFS/SDS mixtures showed weaker synergism, with minimal SDS incorporation attributed to electrostatic repulsions. Ternary systems displayed intermediate behaviour, with STFS and C₁₂E₆ dominating micelle formation while SDS remained mostly excluded. At higher concentrations (10, 20 mM) in SANS measurements the STFS/C₁₂E₆ tended towards more bulk solution molar ratio mixing behaviour whilst SDS stayed minimally incorporated into the micelle, regardless of concentration.