Log Kkao/w values of cationic surfactants were calculated from the isotherm data. Since the isotherms were nonlinear, the resulting log Kkao/w values were concentration-dependent, spanning over 1-2 log units for each cationic surfactant (Figure ). To compare different surfactants, log Kkao/w values in an isosteric condition (i.e., at a constant Ckao) were interpolated using the Freundlich equation.