Binding of N-Alkylpyridinium Chlorides to Nonionic Micelles

Article abstract of DOI:10.1021/j100307a022

Binding of N-alkylpyridinium chlorides (C₁₀, C₁₂, and C₁₄) to dodecyl oxyethylene ether (C12E6 and C12E8) micelles is determined in the presence of 5 mol m^-3 NaCl at various temperatures by potentiometry which employs an electrode responsive to the surfactants.Binding affinity is expressed in terms of a distribution coefficient, K_x, of a cationic surfactant between the aqueous bulk phase and the nonionic micellar phase, and is larger for an alkylpyridinium cation with a longer hydrocarbon chain.The values of K_x are divided into three regions depending on the mole fraction of bound cationic surfactant in a micelle, X.At X < 0.02, K_x remains constant, while for 0.02 < X < 0.2, the binding affinity decreases until it attains a plateau at X > 0.2.The constant K_x values reflect an intrinsic binding affinity (K₀).With increase in X, electrostatic repulsion among bound cationic surfactants causes decreased K_x values, which may be analyzed by a simple electrostatic theory to estimate the position of bound cationic head groups.From the temperature dependence of K₀, it is found that the binding process is nearly athermal for C12E8 micelles but exothermic for C12E6 micelles, the latter associated with the growth of micellar size with temperature.