Synthesis and surface properties of anionic gemini surfactants with amide groups

Abstract

Novel anionic gemini surfactants, 1,2-bis( N- β-carboxypropanoyl- N-alkylamino)ethane (2C n enAm; n is hydrocarbon chain length of 6, 8, 10, 12, or 14), with two hydrocarbon chains, two carboxylate groups, and two amide groups, were synthesized by three-step reactions. Their solution properties were characterized by equilibrium and dynamic surface tension, steady-state fluorescence spectroscopy of pyrene, and dynamic light-scattering techniques. The surface tension measurements of 2C n enAm give low critical micelle concentrations (cmc), great efficiency in lowering the surface tension, and strong adsorption at air/water interface. Gemini surfactants behave normally with the logarithm of cmc decrease linearly with the chain length. In addition, adsorption and micellization behavior of 2C n enAm was estimated by parameter of p C 20, cmc/ C 20, and standard free energy (Δ G 0 mic and Δ G 0 ads); they are significantly influenced by hydrocarbon chain length, and the adsorption is promoted more than the micellization as chain length becomes longer. The results of dynamic light-scattering and fluorescence quenching indicate that small micelles of 2C n enAm are observed at the concentrations above the cmc, and further large particles are also seen. Further, from the dynamic surface tension measurements, it is found that the shorter hydrocarbon chain length of 2C n enAm, the faster the rate of decrease of surface tension.