VISCOSITIES OF ANIONIC NONIONIC MIXED SURFACTANT SYSTEMS

The viscous property of anionic-nonionic mixed surfactant systems in aqueous solutions is described. The systems studied are sodium dodecyl sulfate (SDS)-alkyl poly(oxyethylene) ethers (CmPOEn; m = 12, 14, 16, and 18, n = 10, 20, 30, and 40). In the single system, the relative viscosity of the nonionic surfactant is larger than that of SDS and increases with increasing number of ethylene oxide. In mixed systems the relative viscosity shows maximum at the mixed molar ratio of SDS around 0.3, except for the SDS-C16POE40 system. The mixed systems having longer alkyl and/or polyoxyethylene chain lengths in the nonionic surfactant have a larger relative viscosity at any mixed ratio. The system in which the mixed micelle forms easily has a positive deviation from the ideal value. The relative viscosities of the surfactants in 0.1 M NaCl solution decrease linearly with an increase in the mixed molar ratio of SDS. It is considered that the relative viscosities in the mixed solutions show a maximum due to the electroviscous effect of a mixed solution being larger than that of a single solution. © 1990.