Self-assembly of alcohol ethoxylate non-ionic surfactants in aqueous solution

Abstract

Four alcohol ethoxylates with general formula C _n E _m (where C = methylene or methyl, E = oxyethylene, n = 11, 13, 15 and 17 and m ≈ 40) have been synthesised by anionic polymerisation initiated by the appropriate alcohol and characterised by gel-permeation chromatography (GPC) and NMR spectroscopy. Their self-assembly in aqueous solution was investigated by surface tension and static and dynamic light scattering. All four surfactants associated by a closed process to form micelles. Critical micelle concentrations (c.m.c.), surface tensions at the c.m.c., molecular areas in the air/water interface at the c.m.c., and micelle association numbers were obtained and compared with corresponding values previously measured for related surfactants. Phase diagrams for thermally reversible gelation of concentrated solutions were defined. Gels with copolymer concentrations up to 70 wt.% were isotropic when examined by polarised light microscopy, consistent with cubic symmetry.