Wormlike Micelles of Binary Polyoxyethylene Alkyl Ether Mixtures C10E6 + C14E6 and C14E8 + C14E6

Abstract

The wormlike micelles formed with the binary mixtures of surfactant polyoxyethylene alkyl ethers (CiEj), C10E6 + C14E6 and C14E8 + C14E6, were characterized by static (SLS) and dynamic light scattering (DLS) experiments. The observed Kc/ΔR0 as a function of the surfactant concentration c have been successfully analyzed with the aid of the light scattering theory for micelle solutions, thereby yielding the molar mass Mw(c) of the micelle as a function of c along with the cross-sectional diameter d of the micelle. The mean-square radius of gyration <S2> and the hydrodynamic radius RH as functions of Mw have been well described by the theories for the wormlike spherocylinder model. The length of the micelles at fixed c and temperature T steeply increases with increasing weight fraction wt of C14E6 in both of the surfactant mixtures, implying that the micelles greatly grow in length when the surfactant component with longer alkyl group or with shorter oxyethylene group increases in the mixture. The results are in line with the findings for the micelles of the single surfactant systems where the CiEj micelles grow in length to a greater extent for larger i and smaller j. Although the values of d do not significantly vary with composition of the surfactant mixture, the stiffness parameter λ−1 remarkably decreases with wt in both of the mixtures, indicating that the stiffness of the micelle is controlled by the relative strength of the repulsive force due to the hydrophilic interactions between oxyethylen groups to the attractive one due to the hydrophobic interactions between alkyl groups among the surfactant molecules.