Spin labeling electron spin resonance study of the shape of nonionic detergent micelles

Abstract

The size and shape of nonionic micelles in aqueous solutions and the changes in these systems at the cloud point have not yet been unambiguously determined. The electron spin resonance (ESR) spin labeling cannot always determine the size and shape of the micelles but the ESR lineshapes of the fatty acid spin probe in the C 12E 8 micellar system show that the micelles are probably small and spherical while in the C 12E 6 system they are rod-like. In both systems no spectral changes were observed above the cloud point indicating that the micelles form only loose aggregates as the system becomes optically turbid. At still higher temperatures in the C 12E 6 micellar system demixtion occurred giving rise to flocculae of lamellar phase suspended in aqueous solution of surfactant.