Viscosity Adjustment of Aqueous Micellar Solutions of Gemini Surfactants by Interaction with Additional Surfactants

摘要

The viscosity of aqueous micellar solutions depends on the size and shape of the aggregates and thus can be adjusted by addition of another surfactant interacting with the original component, which alters the geometry of the molecule-pair consisting of two surfactants and influences strongly the size and shape of the mixed micelles. Etha-nediyl-α,ω-bis(dimethyl dodecyl ammonium bromide), referred to as C_(12)-2-C_(12)·2Br, forms generally large micelles. Addition of a cationic surfactant (dodecyltrimethylammo-nium bromide, C_(12)TMABr) or a nonionic surfactant (alkyl polyoxyethylene ether, CmEn), the mixed micelle size is reduced violently since the electrostatic repulsion between the same charged heads of C_(12)-2-C_(12)·2Br and C_(12)TMABr or the steric hindrance of the PEO chain of CmEn in the palisade layers of the mixed micelle, which leads to a decrease in the packing parameter P of the molecule-pair. As a result, the zero-shear viscosity (η_0) of the mixed solution reduces rapidly. In contrast, on adding an oppositely charged surfactant, η_0 of the mixed solution increases strongly since the P of the molecule-pair increases through electrostatic attraction between the oppositely charged heads. The typical cases occur in the mixtures of the anionic gemini surfactant, O,O'-bis(sodium 2-lauricate)-p-benzenediol C11pPHCNa, and the cationic surfactant C_(12)-2-C_(12)·2Br, C_(12)TMABr or its homologue with a different size of heads.