Surface Properties of Cationic Gemini Surfactants and Their Interaction with Alkylglucoside or -maltoside Surfactants

The interaction of a series of cationic gemini surfactants (surfactants containing two hydrophilic groups and hydrophobic groups in the molecule) with decyl-β-maltoside, decyl-β-glucoside, and dodecyl-β-maltoside at pH = 9 in 0.1 M NaCl at 25 °C has been investigated. The five cationic gemini surfactants are [C12H25(CH3)2N+(CH2)4N+(CH3)2C12H25]·2Br- and [C10H21(CH3)2N+−spacer−N+(CH3)2C10H21]·2Br- with four different spacers: −(CH2)4−; −CH2CH(OH)CH(OH)CH2−; −CH2CH2OCH2CH2−; −CH2CH(OH)CH2−. The results illustrate the effects of steric and electrical factors on mixed monolayer and mixed micelle formation and of surfactant−surfactant interactions there. The cationic gemini surfactants and their mixtures with either the alkylmaltoside or the alkylglucoside show stronger interactions at the air/water interface than comparable conventional cationic surfactants (with single similar hydrophobic and hydrophilic groups) and a greater preference for adsorbing at the air/water interface relative to mixed micelle formation in the solution phase. Mixtures containing cationic geminis with hydrophobic spacers showed packing contraction at the air/water interface; those with hydrophilic spacers, packing expansion. Interaction, both in mixed monolayer formation at the air/water interface and in mixed micelle formation in the solution phase, is always stronger with the decyl glucoside than with decyl maltoside. The decyl cationic gemini with smallest spacer shows strongest interaction with the decyl glucosdie or maltoside at the air/water interface and weakest interaction in mixed micelle formation.