Molecular interactions involving aqueous Triton X-100 micelles and anionic surfactants: Investigations on surface activity and morphological transitions

The micellar solutions of nonionic surfactant Triton X-100 (TX-100) were investigated in the presence of several anionic surfactants, namely sodium 1-butanesulfonate, sodium 1-decanesulfonate, sodium octanoate, sodium perfluorooctanoate, sodium decanoate and sodium alkyl sulphates. The resultant structures formed have been analysed using cloud point (CP), wettability and scattering techniques (DLS and SANS). CP and DLS show marked morphological changes for existing TX-100 micellar solutions in presence of an anionic surfactant depending on its respective hydrophilicity or hydrophobicity. Hydrophobic anionic surfactants induced strong demicellization effect and shifted clouding temperature to higher values. SANS study shows typical transition in ellipsoidal shaped micelles of TX-100 based on the specific interactions. The analysis of SANS data revealed that ellipsoidal shaped TX-100 micelles transform to smaller ellipsoidal mixed micelles with lower axial ratio and smaller aggregation number. Wettability of TX-100 aqueous solution on PTFE surface changes significantly on addition of small amount of anionic surfactant. The water penetration through porous channels of packed PTFE powder in a metal cylinder depicts reduction in wettability due to formation of stable micelles in presence of fluorinated surfactants. The specific changes in CP and morphology of TX-100 micelles are explained in terms of critical molecular interactions as influenced by the hydrophobic chain length and polar head group of surfactants.