The binary and ternary phase behavior of a series of di-n-alkyldimethylammonium bromide surfactants has been investigated. The formation of clear, isotropic microemulsion phases in ternary mixtures with oil and water has been mapped on composition diagrams and this has been correlated with their binary phase behavior in water and with conductivity measurements of the water connectivity in the system.
Macrocyclic compounds are used to complex metal counterions and thereby change the interfacial properties of anionic micelles and mica. Macrocyclic cryptate ligands (C221 or C222) or the crown ether (18-crown-6) were added to surfactant solutions of lithium, sodium, potassium, calcium, or barium dodecyl sulfate. This resulted in lower critical micelle concentrations, decreased aggregation numbers, which are insensitive to added salt, and larger interfacial areas per molecule. Surface forces measurements show that the mica counterion complexation effects are less dramatic. Addition of C222 to potassium or barium salt solutions results in significant increase in the separation of the mica surfaces at "contact", but almost no change in the surface potential. These results provide a basis for comparing counterion effects for colloidal interfaces with fixed and labile surface charges.
The micellization of SDS in the presence of cryptand C222 and 18-crown-6 was investigated to determine what counterion-specific effects control the aggregation of anionic surfactants. Complexation of the sodium alters the cmc, aggregation number, and ionization of the micelles considerably. The results are discussed in terms of changes in the double layer surrounding the micelle which induce reorganization of the micelle. and P. W. Carr for helpful discussions in the course of this work, and D. D. Thomas for making available the fluorometer used for the aggregation number determinations.
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