ON HEMIMICELLE FORMATION AT OXIDE/WATER INTERFACES

Abstract

Publisher Summary This chapter describes the phenomena of hemimicelle formation at oxide/water interfaces involving the association of adsorbed ions. Each hemimicelle contains more than 20 surfactant ions. For both dodecyl sulfonate and dodecylbenzene sulfonate, the size of the hemimicelle is increased with increase in salt concentration. The effect of salt on hemimicelle formation is similar to the salt effect on micelle formation. The formation of hemimicelles is taken as a surface analog of micelle formation in bulk solution. Hemimicelle formation is dependent on the electrical nature of the interface and the salt concentration. In the chapter, the proposed model allows calculation of the size of the hemimicelle from the available adsorption data. The model is further used to explain the effect of pH, ionic strength, the number of carbon atoms in the hydrocarbon chain, and the effects of benzene rings in the hydrocarbon chain. Correspondence between the hemimicelle formation and micelles in bulk solution is taken as indicative of the “hydrophobic effect” in both cases. Hemimicelles are more difficult to form at lower pHs or high surface potentials. This is attributed to the exclusion volume effect of bulky surfactant ions relative to the smaller inorganic counter ions.