No abstract

The interfacial and thermodynamic properties of nonionic surfactants and their mixtures are of both theoretical and practical interest. The nonionic surfactants used in this study are polyoxyethylene (10) alkyl ether [CnE10; m ) 10 and n ) 12, 16] and N-decanoyl-N-methylglucamine (MEGA-10). The critical micelle concentrations of pure surfactants and their mixtures were determined by surface tension measurements at different mixed ratios and temperatures. Interfacial parameters such as the maximum surface excess (Γmax) and the minimum area per molecule (Amin) at the air/water interface were also determined from surface tension data. Standard thermodynamic parameters of micellization and adsorption were also computed and discussed. Steady-state fluorescence studies were also carried out to determine the micellar aggregation number (Nagg) and the microenvironment/polarity in the mixed micelle from the I1/I3 ratio. The interaction parameters that measure the interaction between the surfactant molecules in the mixed micelle were computed by Rubingh's approach. 1 H NMR was also used to investigate the interaction between the 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.

The interfacial and thermodynamic properties of SDBS/C 12 E 10 mixed system in aqueous solution in the presence of additives, i.e., poly(ethylene glycol) 400, sucrose, and urea have been investigated. The critical micelle concentrations (cmc) were determined by both surface tension and conductivity measurements. The maximum surface excess (Γ max ) and minimum area per molecule (A min ) were determined from surface tension data. The thermodynamic parameters of micellization and adsorption were computed and discussed. The enthalpyentropy compensation effect was observed in all the cosolvent systems. The partition coefficient of these hydrophilic additives between the micelle and the solvent was found to be zero. The transfer quantities, which are sensitive to the solvent structure, were also computed. The interaction parameters between the surfactant molecules both in the presence and absence of additives were evaluated by Rubingh's approach. Micellar aggregation number (N agg ) for the mixed system in the presence and absence of additives were determined by fluorescence measurements. 1 H NMR was also used to study the behavior of surfactants in mixed micelles.