An evaluation of the electrostatic free energy of micelle formation

The acid dissociation constants, K, of decyl- and dodecylammonium chloride were determined from pH measurements, in the absence of added salt, just above and just below the critical micelle concentration. The change in K is related to the electrostatic work of forming the micelle. This work is 2.53 kT and 3.75 kT, respectively, for the C₁₀ and C₁₂ salts. Upon comparing these values with similar values obtained by other means for different micelle-forming molecules of equal hydrocarbon chain length, one finds a correlation between the change in K and the specific character of the ionizable group. This specific effect is discussed in terms of the surface geometry of the micelle and the transmission of electrostatic effects through the micelle hydrocarbon cavity of low dielectric constant.