pH controlled size/shape in CTAB micelles with solubilized polar additives: A viscometry, scattering and spectral evaluation

In this manuscript we report pH induced micellar transition in aqueous solution of cetyltrimethylammonium bromide (CTAB) in the presence of three weakly polar aromatic additives viz. p-toluic acid, p-cresol and p-toluidine scrutinized by viscosity, nuclear magnetic resonance (NMR), dynamic light scattering (DLS) and small-angle neutron scattering (SANS) measurements. Interaction between these additives and CTAB micelles changes the size and shape of the micelles. Variation in pH alters the charge on the polar group and leads to protonation/deprotonation of acidic/basic group of the additives. Depending upon the pH of solution additives interact with CTAB micelles and accordingly change the solution behavior/aggregation characteristics. Morphological changes of surfactant aggregates as a function of additive concentration and pH were monitored by SANS measurements. NMR studies reveal a pH dependent location of the additive molecules in the micelles.