| Abstract
| - A surface-active arenediazonium ion, 4-hexadecyl-2,6-dimethylbenzenediazonium ion, 16-ArN2+, wasused as a chemical trapping probe of the concentrations of weakly basic nucleophiles in the surfactant filmbetween the aqueous and oil domains of opaque relatively long-lived C12E5/octane/water macroemulsionsas 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 surfactantfilm. Product yields from trapping of the available nucleophiles, H2O, the terminal OH group of C12E5, andCl-, were used to estimate average hydration numbers of all aggregates present in the macroemulsionsas a function of increasing temperature and added NaCl. At 19.9 °C, the average hydration number in themacroemulsions is 2.5, compared to a 70% larger value of 4.2 in C12E6 micelles at 20 °C obtained previouslyby chemical trapping. Average hydration numbers decrease with increasing temperature and with addedNaCl at constant temperature as macroemulsion structure changes from oil-in-water type through thebalanced point to water-in-oil type. These results are consistent with the oriented wedge theory ofmacroemulsion stability. Chemical trapping estimates of Cl- concentrations within the interfacial layerof the surfactant film of the macroemulsions show that the molarity of Cl- in the aqueous region of theinterfacial layer is always about 10% greater than the Cl- molarity in the aqueous domain. Thus, Cl-, andprobably Na+, move freely between the bulk aqueous domain and the surfactant film of the macroemulsions,contradicting an assumption of adsorption/depletion model for the effect of lyotropic salts on the hydrationof the interfacial layer. These results demonstrate the potential of chemical trapping for probing surfactantfilm compositions of opaque macroemulsions.
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