Triton X-100 micelles modulated by solubilized cinnamic acid analogues: The pH dependant micellar growth

Aqueous micellar solutions of a nonionic surfactant p-tert-octylphenoxy polyethylene (9.5) ether, Triton X-100 (TX-100) in the presence of cinnamic acid and its hydroxyl derivatives viz. p-coumaric acid, caffeic acid, ferulic acid and sinapic acid were examined by cloud point (CP), viscosity, dynamic light scattering (DLS), nuclear magnetic resonance (NMR) and small-angle neutron scattering (SANS) measurements. These solubilizates influence the CP, viscosity and micelle size of TX-100 depending on their hydrophobicity. Cinnamic acid, a biomedically useful compound displayed maximum growth in the micelles and was therefore studied in detail. We found that an increase in the cinnamic acid concentration, a decrease in pH and the presence of sodium chloride all favour the micellar growth at low temperature. The location of cinnamic acid in micelles was elucidated from 1H NMR. SANS study showed that ellipsoidal micelles transform into rod-like on solubilization of cinnamic acid which otherwise change to spherical ones in alkaline medium.