Aqueous Properties of an Anionic Gemini Surfactant with N,N'-Dialkylamide and Carboxylate Groups in Solubilizing System

The aqueous properties of an anionic gemini surfactant, (CH2)2[NCO(C11H23)C2H4CO2Na]2, 212, and 212/sodium dodecanoate(soap) mixtures, were studied in the presence of solubilizate of Orange OT, 1-(o-tolylazo)-2-naphthol. The following parameters were measured:critical micelle concentration(cmc), micelle composition, and solubilization capacity for Orange OT. For the sake of comparison, the properties of SDSa (SDSa=sodium N-dodecanoylsarcosinate, the monomer corresponding to the 212), and mixtures of SDSa/soap, were also investigated. The cmc value of 212 in the solubilizing system obtained, 1.0mM, approximately corresponds to the second cmc value, 1.6mM, obtained in the non-solubilizing system. This second cmc value is much higher than the first cmc value, 0.04mM, determined by the surface tension method. Whereas, the cmc value of SDSa in the solubilizing system is 10.0mM, and close to that, 10.2mM, determined by the surface tension method in the nonsolubilizing system. The solubilization capacity of 212 for Orange OT is 3.0 times that of SDSa. The micelle compositions of the mixtures of 212/soap and SDSa/soap are 2:1 and 1:1, respectively. The solubilization capacity of the 212/soap mixture is 1.8 times that of the SDSa/soap mixture in the region of lower soap molar ratio. The mixed cmc values, 1.9-5mM, of 212/soap mixture in the solubilizing system are markedly lower than those, 12-16mM, in the non-solubilizing system. These behaviors of 212 may reflect the greater tendency of 212 to release Na+ into the bulk phase, permitting larger solubilized amount of Orange OT.