Abstract
Solution properties of anionic-amphoteric surfactant mixed system in aqueous solutions were studied in terms of surface tension, pH and pNa values, electric conductivity, heat of dissolution, and relative viscosity. This system was sodium dodecyl sulfate (SDS) -Nα, Nα-dimethyl-Nα-lauroyllysine (DMLL). When the mole fraction of DMLL was about 0.7, the cmc values of SDS mixed with DMLL were minimum and the pH values, heats of micelle formation, relative viscosities, and effective volumes maximum. The degree of ionic dissociation of mixed micelle (α) increased with the addition of amphoteric surfactant (DMLL) to SDS solution. Moreover, the values of α increased with increasing molar ratio of DMLL involved. The electric conductivities of the mixed surfactant solutions were dependent on the molar ratio of DMLL involved. It is considered that these phenomena are caused by hydrophilic interactions between SDS and DMLL molecules in mixed micelles.
