Effect of Spacer on Surface Activity and Foam Properties of Betaine Gemini Surfactants

Abstract A series of betaine-type Gemini surfactants (C s -BGS, where C is the methylene part of the spacer, s = 2, 4, 6) were synthesized from sodium 3-chloro-2-hydroxypropanesulfonate, oleamidopropyl dimethylamine and bromoalkane. The chemical structure of the prepared compounds was confirmed by 1 H NMR, 13 C NMR, IR spectra, and elemental analysis. Their critical micelle formation concentrations (CMC) in the aqueous solution at 25 °C were determined by measuring the surface tension and the electrical conductivity. As the length of the spacer increased, the values of their CMC and γ cmc also increased. The surface tension measurements of C 2 -BGS revealed that the surfactant possesses a low CMC, is very efficient in reducing the surface tension, and is very strongly adsorbed at the air-water interface. In addition, the adsorption and micellization behavior of C s -BGS was estimated from the efficiency of surface tension reduction (pC 20 ), minimum average surface area per surfactant molecule (A min ), and standard free energies of micellization and adsorption. These properties are significantly affected by the spacers and the adsorption is more favored than the micellization.