Synthesis and Surface Tension Study of the Spacer Chain Length Effect on the Adsorption and Micellization Properties of a New Kind of Carboxylate Gemini Surfactant

Abstract

AbstractA series of carboxylate gemini surfactants, which contain two hydrocarbon chains linked by amide groups, two carboxylate groups, a flexible alkane spacer were synthesized by three‐step reactions and named alkylidene–bis‐(N,N′‐dodecyl‐carboxypropylamides) (2C12H25CnAm; n = 2, 3, 4, 6, 8 is the number of methylene groups of the spacer), their structures were confirmed by FTIR,1H NMR, and LC–MS/TOF, and their purity checked by HPLC. The micellar properties with increasing spacer chain length of these gemini surfactants were determined by surface tension methods. The critical micelle concentration (CMC) varies slightly with spacer chain length; surface tension at CMC(γCMC), the tendency of micellization versus adsorption, CMC/C20, the minimum area per surfactant molecule at the air/solution interface (ACMC), all decrease with increasing spacer chain length; surface reduction efficiency, pC20, the surface excess at the air/solution interface (ГCMC) increase with increasing spacer chain length. The results probably indicate that increasing spacer chain length of these carboxylate gemini surfactants will increase spacer incorporation into the double hydrophobic chain.