MICELLE FORMATION BY PURE NONIONIC SURFACTANTS AND THEIR MIXTURES

Micelle formation by pure nonionic surfactants and their mixtures has been investigated with static and dynamic light scattering and with fluorescence probe measurements. The surfactants used in this study are alkyl poly(oxyethylene) ethers (CmPOEn; where m = 12, 14, and 16, at n = 20; n = 10, 20, 30, and 40, at m = 16). In the single component nonionic surfactant system, the hydrodynamic micellar size increases with an increase in alkyl or poly(oxyethylene) chain lengths. The aggregation number of single component surfactant micelles increases with increasing alkyl chain length or with decreasing number of oxyethylene groups. Moreover, the micropolarity in the micelle decreases as the length of the alkyl group increases or that of the oxyethylene group decreases. In the case of the C16POE10-Cl6POE40 mixed surfactant system, at 0.5 mole fraction C16POE40 at fixed concentration above the critical micelle concentration, the molecular weight of the mixed micelle shows a maximum and the concentration of micelles exhibits a minimum. The hydrodynamic micellar size in the mixed system increases with an increase in the mole fraction of C16POE40 and remains constant above a mole fraction of 0.5. The micropolarity in the micelle increases with an increase in the mole fraction of C16POE40. The hydrophilic part of the mixed micelle seems to be compact due to the penetration Of C16POE10 and C16POE40 monomers into the poly(oxyethylene) shell of the micelle.