Autocatalysis in liquid/liquid surfactant transfer

Abstract

Equilibrium and transfer properties of two surfactants (a non-ionic one, Brij5, and a cationic one, CTAB) were studied in water/oil biphasic systems. Water/air surface tension measurements provide information on both the partition coefficient and also on the type of aggregates formed: classical micelles or swollen micelles (oil-in-water microemulsion). A clear correlation is established between the type of aggregates and the kinetics recorded during transfer of the surfactant from the organic to the aqueous phase. Indeed, an accelerating kinetics is obtained for every system leading to the formation of swollen micelles. This is the first example of autocatalytic dynamics observed in biphasic conditions for a non-reactive system. This non-linear behavior, correlated to the Critical Aggregation Concentration, confirms the contribution of an interface mediated pathway, known as the “budding mechanism”, to the formation of microemulsion for both non-ionic and ionic surfactants.