Hofmeister effect on micellization, thin films and emulsion stability

Abstract

The Hofmeister effect on the critical micelle concentration (CMC), the thin liquid film electrostatic disjoining pressure (Π(el)) and the critical coalescence pressure of emulsion drops (P(CR)) were investigated. For CMC literature data were used, but Π and P(CR) were measured by us. The essence of the theoretical approach was to modify existing theories of CMC and Π(el) by using generalized Gouy equation and dimensionless surface potential (Φ(S)), involving the counterion specific adsorption energy (u(0)). The computational procedure of u(0) does not involve any adjustable parameters. Linear dependences of ln(CMC), Φ(S) and P(CR) on u(0) were found in conformity with Hofmeister series. The experimental slopes of ln(CMC) and Φ(S) vs. -u(0)/k(B)T were negative and very close to the theoretical ones. A hypothesis was put forward for explanation of the positive slopes of P(CR) on u(0). The obtained results suggest that the counterion specific adsorption energy u(0) encompasses all major factors, involved in the Hofmeister effect for the studied phenomena. If this is confirmed by analysis of more phenomena, revealing Hofmeister effect, one could claim that u(0) is the factor controlling the Hofmeister effect and a powerful tool for its study.