Surface properties of zwitterionic surfactants: III. Effect of halide ions on properties of a betaine and its interaction with cationic surfactants

Abstract

The effects of halide ions on the surface properties of N-dodecyl- N-benzyl- N-methylglycine (C 12BMG) and on the interaction of C 12BMG with cationic surfactants are described. The addition of HCl decreases the surface activity of C 12BMG, while the addition of halide ion at constant pH increases it in the order Cl − < I −. The observed effect of halide ions is similar to their effect on cationic surfactants and is explained as the result of: (1) displacement of the C 12BMG-C 12BMGH + equilibrium in a forward direction and (2) compression of the electrical double layer. Instructions between the two surfactants in aqueous C 12BMG-cationic mixtures in the presence of halide ions, measured by β σ and β M, the molecular interaction parameters for mixed monolayer and mixed micelle formation, respectively, show two effects that are opposite to that observed in C 12BMG-nonionic mixtures: (1) an increase in interaction in the presence of 0.1 N sodium halide and (2) greater interaction in the presence of Br − than Cl −. These effects are believed to be due to increased lateral interactions as a result of closer packing of the surfactant molecules at the interface.