Association characteristics of synthetic non-ionic surfactants in aqueous solution

Abstract

The mode of association of three novel synthetic non-ionic surfactants CH₃O[CH₂]₆CH(OCH₃)CH(OCH₃)[CH₂]₈[O.CH₂CH₂]_xOH, (x= 6, 8, 18) has been determined in aqueous solution by total intensity light scattering, vapour-pressure osmometry and solubilisation techniques. The association of the hexaoxyethylene compound has been described using association models which assume micellar growth by the stepwise addition of monomers to primary micelles formed at the critical micelle concentration (c.m.c.). The scattering intensity from solutions of the other two surfactants increased non-linearly with concentration with no significant inflection attributable to a c.m.c. The association of the octadecyloxyethylene compound conformed to a stepwise process with successive equilibrium constants of equal magnitude, whilst that of the octaoxyethylene compound was most satisfactorily described using a cooperative association model.