Micelle Structure in Aqueous Solutions of Polyoxyethylene Surfactants

Abstract

We have investigated the size of micelles formed in aqueous solutions of the nonionic polyoxyethylene surfactants C8E5, C12E6, C12E8 and C16E8 in the isotropic phase as a function of temperature below the lower consolute boundary(LCB) and of concentration below the mesophase boundaries by elastic and quasielastic neutron scattering. We find little variation in micelle size and shape throughout the range of conditions studied, provided intermicellar interactions are taken into account in terms of their structure factor. The latter is calculated assuming that the direct interaction potential is hard sphere plus a short ranged attractive tail. Far away from the LCB the attractive part is negligible, but becomes important upon approach of the LCB. At higher concentrations the predominant interaction is hard-sphere repulsion. In particular, near the mesophase boundaries micellar growth is minor, if present at all.