Structural Effect on Surface Activities of Anionic Surfactants Having N-acyl-N-methylamide and Carboxylate Groups

The simultaneous presence of N-acyl-N-methylamide and carboxylate groups in the surfactant molecule produces some unique interfacial properties in aqueous media. These are ascribed to the steric effect of hydrogen bonding between the two groups. Properties of sodium N-dodecanoyl-N-methyl-β-alanate (SDMA) and N-dodecanoylsarcosinate (SDSa) were compared with those of sodium N-dodecanoyl-N-methyltaurinate (SDMT) and sodium decyloxyacetate (SDOA) in water in 0.1 M NaCl at 30°C. Evidence for the steric effect on micellization includes the order of increasing Amin (the minimum area occupied by the surfactant molecule at the air/water interface) and values of the critical micellar concentration (cmc)/C20 ratio (a measure of the factors inhibiting micellization relative to adsorption at the air/water interface): SDOA