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The concentration dependent properties exhibit a break point due to the micellization.The CMC of surfactant is usually determined by plotting those properties as a function of concentration. The other important property of ionic surfactant solutions is the degree of micellar counterion dissociation, which has been used to be quantified by the two-site model (7,8). From this simple model one can calculate the α by using the concentrations of "free" ions in the aqueous bulk phase and "bound" ions in micellar phase. The model has successfully The MQAE probe was developed to study the transport of chloride ion in liposomes (11).The MQAE are highly polar and membrane impermeant, which has suitable physical properties for measurement of the concentration of free chloride ion. When the cationic MQAE is introduced to cationic surfactant solutions, the MQAE will tend to partition in aqueous bulk phase due to the low octanol-water partition coefficient in addition to the electrostatic effect.The fluorescence behavior of water-soluble MQAE can be expected to related to the chloride ion concentration in aqueous bulk phase. Fig. 2 shows the Stern-Volmer plots for quenching of MQAE fluorescence by various cationic surfactants. The fluorescence intensities of MQAE 5 were found to decrease in the presence of CTAC, TTAC, TDBAC and DAC. The observed quenching can be ascribed to the free chloride ion dissociated from the surfactant. All experimental data gave linear plots below their CMCs. The slopes of plots, K SV , below CMC are summarized in Table 1. The K SV for CTAC agreed very closely with that of NaCl. The K SV for surfactant monomer tend to decrease with decreasing length of the alkyl chain. The decrease in

A group contribution method is proposed to predict the cmc of aqueous binary mixtures of surfactants. The interaction parameters of the molecule's functional groups, including hydrophilic groups, were determined from the cmc values of mixed systems. The calculated cmc's were in good agreement with the experimental ones. The cmc curves in a series of mixed systems, e.g., lithium perfluorooctanesulfonate (LiFOS)-lithium dodecyl sulfate (LiDS), -lithium tetradecyl sulfate (LiTS), and -lithium hexadecyl sulfate (LiHS), were fitted by the same interaction parameters. The mutual solubilities of fluorocarbon and hydrocarbon surfactants in the micellar phase were also studied. The hydrocarbon-rich micelles solubilized the fluorocarbon surfactants to a certain extent, whereas the fluorocarbon-rich ones solubilized the hydrocarbon species sparingly. We could predict the cmc of nonideal binary mixtures by the use of cmc, .Kg, molecular structure data of pure components, and the group interaction parameters.

The degree of micelle ionization of gemini surfactants has been investigated by using halide-sensitive fluorescence probes (e.g., 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ)). The fluorescence is quenched by the free bromide ions dissociated from surfactants. The degree of micelle ionization increased with increasing spacer chain length, but it decreased with increasing surfactant concentration. The Stern-Volmer plot gave two inflection points (i.e., not only at the cmc but also far above the cmc). The second inflection point suggested spherocylindrical micellar growth with decreases in the degree of micelle ionization. The spherocylindrical micellar growth was depressed with increasing spacer chain length, whereas it was enhanced with increasing tail chain length. The degree of micelle ionization of spherocylindrical micelles depended on the concentration and chain length of gemini surfactants. The change in SPQ fluorescence spectra upon hydrogenation was utilized to evaluate the solubilization site in micelle solutions. The dissolved SPQ in water was instantly reduced by the addition of NaBH4, resulting in abrupt changes in fluorescence intensity and spectral shift. All of the SPQ in micelle solution was also instantly reduced by NaBH4, indicating the existence of SPQ in the water bulk phase, but its fluorescence intensity increased upon the solubilization of hydrogenated SPQ into micelles.

A new cationic surfactant, 1,1,2,2-tetrahydroheptadecafluorodecylpyridinium chloride (HFDePC), quenches the fluorescence emission from pyrene in pure micelles but hardly quenches it in mixed micelles composed of fluorocarbon and hydrocarbon surfactants. Pyrene is located in hydrocarbon-rich micelles, and its fluorescence is quenched by cetylpyridinium chloride. However, HFDePC is mainly solubilized in fluorocarbon-rich micelles, and a collision probability between pyrene and HFDePC would be small within the lifetime of the excited pyrene. That is, the depression of quenching by HFDePC could be ascribed to the coexistence of two kinds of mixed micelles. The effects of addition of salt and temperature toward the depression of quenching were also examined.