Charge effect of a cationic surfactant on the structure and growth of a nonionic surfactant micelle

Abstract

We have studied the charge effect of a cationic surfactant (Dodecyl Trimethyl Ammonium Bromide: DTAB) on the structure and growth of a nonionic surfactant micelle (penta-ethyleneglycol mono n-dodecyl ether: $C_{12}E_5$). Hydrodynamic diameter($D_H$), aggregation number($N_{agg}$), micellization concentration(CMC), and second virial coefficient($A_2$) of the $C_{12}E_5$/DTAB mixed systems ranges from 100 mol% to 91 mol% have been measured by static and dynamic light scattering. Friction was also measured with a viscometer to analyze a value, $k_D$. In a dilute regime the diffusion constant increases as the concentration of the micelle solution increases : an interaction potential is repulsive, and the repulsive potential produces a positive . The charged surfactant makes the interaction term of dominant, and thus the diffusion constant increases. When the mixing mole fraction of $C_{12}E_5$/DTAB is smaller than 95mol%, many charges insert in micelles, which makes the micelles disintegrate into monomers.