The surface activity of salts added to water is orders of magnitude lower than that of surfactants. Sodium trifluoromethanesulfonate (NaTf) produced a change in surface tension with concentration, Δγ/Δc, of -13.2 mN·L/m·mol. This value is ca. 4-fold larger than those of simple salts and that of methanesulfonate. This unexpected surface effect suggested that positively charged micelles containing Tf could exhibit interesting properties. Dodecyltrimethylammonium triflate (DTATf) had a higher Kraft temperature (37 °C) and a lower cmc (5 × 10(-3) M) and degree of dissociation (0.11) than the chloride and bromide salts of DTA. Above the Kraft temperature, at a characteristic temperature t(1), the addition of NaTf above 0.05 M to a DTATf solution induced phase separation. By increasing the temperature of the two-phase system to above t(1), a homogeneous, transparent solution was obtained at a characteristic temperature t(2). These results, together with well-known triflate properties, led us to suggest that the Tf ion pairs with DTA and that the -CF(3) group may be dehydrated in the interfacial region, resulting in new and interesting self-aggregated structures.

Chemical trapping of bromide ions in reverse micelles prepared with hexadecyltrimethylammonium bromide, CTAB, in n-dodecane/CHCl3 and isooctane/n-hexanol has been obtained for 2,4,6-trimethylbenzenediazonium (1-ArN2 +) and 2,4-dimethyl-4-hexadecylbenzenediazonium (16-ArN2 +) tetrafluoroborates. Quantitative analysis of the reaction products of 1-ArN2 + and 16-ArN2 + with water and bromide ion, the corresponding phenol and bromo derivatives, and comparison with appropriate standard curves yielded the local concentrations of Br- in the water pool, [Br]f, and micellar interface, [Br]b, in reverse CTAB micelles prepared in n-dodecane/CHCl3 and isooctane/n-hexanol. The determination of [Br]b in reverse micelles by chemical trapping with 16-ArN2 + can be obtained after correction for probe distribution between the reverse micelle and the organic solvent, especially in the case of n-dodecane/CHCl3. This correction was possible after demonstrating that 16-ArN2 +, upon dediazoniation in wet n-dodecane/CHCl3, yields exclusively the corresponding bromo derivative. A Poisson−Boltzmann (PB) equation above a water/detergent molar ratio, W/S, of 14 appropriately describes the values of [Br]f. Comparison of the experimental values of [Br]b with those predicted by PB with changing W/S suggest that 16-ArN2 + extends from the interface 0.6−1.2 nm with increasing W/S. Both PB calculations and experimental data indicate that the degree of counterion dissociation from CTAB reverse micelles in n-dodecane/CHCl3 reaches a value of ca. 0.2 above W/S 15.

The local concentrations of chloride, Clb, and bromide, Brb, in the interface of vesicles prepared with dioctadecyldimethylammonium chloride, DODAC, or bromide, DODAB, dipalmitoylphosphatidylcholine, DPPC, dimyristoylphosphatidylcholine, DMPC, and mixtures of DMPC, DPPC, and DODAC were determined by chemical trapping by analyzing product yields from spontaneous dediazoniation of vesiclebound 2,6-dimethyl-4-hexadecylbenzenediazonium ion. The values of Cl b and Brb in DODAC and DODAB vesicles increase with vesicle size, in agreement with previous data showing that counterion dissociation decreases with vesicle size. Addition of tetramethylammonium chloride displaces bromide from the DODAB vesicular interface. The value for the selectivity constant for Br/Cl exchange at the DODAB vesicular interface obtained by chemical trapping was ∼2.0, well within values obtained for comparable amphiphiles. In vesicles of DPPC the values of Cl b were very sensitive to the nature of the cation and decreased in the order Ca 2+ > Mg 2+ > Li + > Na + > K + ) Cs + ) Rb + g TMA + . The effect of the cation becomes more important as temperature increases above the phase transition temperature, Tm, of the lipid. The values of Clb increased sigmoidally with the mol % of DODAC in vesicles prepared with DODAC/lipid mixtures. In sonicated vesicles prepared with DODAC and DMPC (or DPPC), the values of Clb reach local concentrations measured for the pure amphiphile at 80 mol % DODAC. These results represent the first extensive study of local concentration of ions determined directly by chemical trapping in vesicles prepared with lipids, synthetic amphiphiles, and their mixtures.