Adsorption and micellization of alkanediyl-bis(dimethyldodecylammonium bromide) in isopropyl myristate/aqueous system

The adsorption and the micellization of a series of cationic Gemini surfactants, alkanediyl-bis(dimethyldodecylammonium bromide), referred as 12-s-12, in the isopropyl myristate (IPM)/aqueous system have been investigated using interfacial tension measurements. These surfactants showed much stronger ability for their adsorption at the IPM/water interface and micellization in the water phase in comparison with the corresponding monomer, C₁₂TABr. The adsorption and micellization behavior of 12-s-12 was found to strongly depend on the length of spacer chain, which was comparable with those studied previously in the air/water system. Compared with the compounds with short spacer chain, the 12-s-12 having a long spacer chain (s ≥ 12) showed complicated behavior for their adsorption and micellization due to the bending of the long spacer chain. Thus, the adsorption process could be divided into two stages. At the beginning stage, the adsorption was diffusion-only controlled and the long spacer chain had a free conformation on the interface. At the second stage, more 12-s-12 molecules crowd into the adsorption layer and forced the long spacer chain to bend strongly in order to make room for the new molecules. This resulted in more and more tight packing of the molecules on the interface and thus a quite large limiting dilational elasticity for 12-16-12 and 12-18-12. The addition of salt greatly promoted the adsorption and micellization of 12-s-12. The present results suggested that the 12-s-12 with s ≥ 12 may be a good emulsifier to construct stable emulsion.