Microphase-enhanced reactions: Simultaneous effects of ion coupling and counterion binding

Abstract

Microphase-induced enhancement of the rate of mass transfer of the reactive species in instantaneous heterogeneous reactions is described by the generalized film theory under quasisteady-state conditions. The diffusive transport of ions which incorporates the ion-coupling phenomenon is represented by the Nernst-Planck equation. The molecular transport is described by the Fickian diffusion. In contrast to the previous investigations, a substantial increase in the relative enhancement factors (about 2 to 6 times) in the two phase reactions (between N,N-diethyl aniline and HCl in the presence of anionic surfactant sodium lauryl sulfate, and between 2,5-dimethyl phenol and NaOH in the presence of cationic surfactant cetyltrimethylammonium bromide) is observed experimentally. This increase in the rate of mass transfer of the reactive species is shown to be caused by the augmentation of the diffusion coefficients of the reactive species owing to the ion-coupling effect. Also, counterion binding of the reactive species on the micellar charged surface is analyzed within the framework of the ion-exchange equilibrium model. The solution of the resulting ion-exchange expressions in conjunction with mass-transfer model predicts the reduction in enhancement factors by 5-15%.