Arenediazonium Salts: New Probes of the Compositions of Association Colloids. 7. Average Hydration Numbers and Cl- Concentrations in the Surfactant Film of Nonionic C12E5/Octane/Water Macroemulsions: Temperature and NaCl Concentration Effects

Abstract

A surface-active arenediazonium ion, 4-hexadecyl-2,6-dimethylbenzenediazonium ion, 16-ArN2+, was used as a chemical trapping probe of the concentrations of weakly basic nucleophiles in the surfactant film between the aqueous and oil domains of opaque relatively long-lived C12E5/octane/water macroemulsions as a function of temperature and added NaCl. The results demonstrate that the chemical trapping method “sees” the composition of the oligooxyethylene or interfacial layer on the aqueous side of the surfactant film. Product yields from trapping of the available nucleophiles, H2O, the terminal OH group of C12E5, and Cl-, were used to estimate average hydration numbers of all aggregates present in the macroemulsions as a function of increasing temperature and added NaCl. At 19.9 °C, the average hydration number in the macroemulsions is 2.5, compared to a 70% larger value of 4.2 in C12E6 micelles at 20 °C obtained previously by chemical trapping. Average hydration numbers decrease with increasing temperature...