A comparison of the counterion binding to ionic micelles in aqueous and nonaqueous systems

• The counterion binding to hexadecyltrimethylammonium fluoride (C16TAF) micelles in three different solvents; water, formamide and ethylene glycol, has been studied both experimentally and theoretically. Self-diffusion measurements by NMR spectroscopy was used as the experimental technique, and the counterion binding was determined for surfactant concentrations up to 20 wt%. The degree of counterion binding was found to be very different in the three solvents; high in water and ethylene glycol but much lower in formamide, with an increase with concentration in the latter system. The Poisson-Boltzman equation was used to calculate how the aggregation number and the dielectrical constant of the solvent affect the counterion binding. A comparison between experimental and calculated values of degrees of counterion binding indicates that the micelles are significally smaller in the non-aqueous systems. The concentration dependence of the counterion binding in formamide was explained as aggregate growth with increasing surfactant concentration.

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