Heats of dilution of sub-micellar aqueous surfactant solutions

Abstract

Heats of dilution of sub-micellar solutions of a series of sodium alkyl sulphates and alkyl-trimethylammonium bromides are reported and two possible interpretations of the observed deviations from simple Debye-Hückel theory are given. The first is in terms of dimerisation of the surfactant ions. The second is that the effective distance of closest approach of ions of opposite charge decreases with increasing temperature because of corresponding decreases in hydrophobic hydration of the alkyl chains of the surfactant ions. Neither interpretation is to be preferred to the other on the basis of evidence currently available.