The Binding of Pentadiyl‐α,ω‐Bis(Dimethyldodecylammonium), a Cationic Gemini 12‐5‐12 Surfactant to Conjugated Carboxylates as Organic Counterions

ABSTRACT The critical micelle concentration (CMC) values of the cationic gemini surfactant pentadiyl‐α,ω‐bis(dimethyldodecylammonium) bromide depend on the hydrophobicity of added conjugated organic carboxylate anions. Nine conjugated counterions, present as sodium salts of organic acids, were studied to expand the correlation to the counterion hydrophobicity effect on the CMC. These added salts are sodium benzoate, sodium o‐fluorobenzoate, sodium o‐chlorobenzoate, sodium o‐bromobenzoate, sodium 2,6‐difluorobenzoate, sodium 3,5‐difluorobenzoate, sodium cinnamate, sodium 3,5‐difluorocinnamate, and sodium sorbate. Three methods, conductivity, fluorescence intensity, and NMR chemical shifts, were employed to obtain CMC values. 1D and 2D NMR spectra yield data on the counterion binding to the micellar interface. A straightforward correlation of the Log (CMC) values and the Log P values of the organic acid, which was deprotonated to serve as the counterion, demonstrates the Log P values can be utilized to predict the surfactant aggregation behavior over an extensive range.