Synthesis, surface activity and performance in "green" shampoo formulations of new carboxybetaine-type surfactants

Novel zwitterionic surfactants-(N-methylalkylamide-derived) [3-(alkylmethylamino)-3-oxopropyl] dimethylammonium acetates (abbr. C(n)DMPAB, n = 10, 12, 14, and 16) have been rationally designed as multifunctional surface active compounds with the intended characteristics toward their application in natural shampoo formulations. The synthetic routes included the alkylation of N-methyl-N-alkylamines with methyl 3-(dimethylamino)propionate, followed by betainization, while the purification steps enabled the isolation of high-purity products for physicochemical analyses. Surface activity and micellization properties of novel C(n)DMPAB surfactants were studied by surface tension isotherms, and their wettability by advancing and receding contact angle measurements utilizing the Wilhelmy method. The aim of these studies was to exhibit the full potential of C(n)DMPAB series compounds as the multifunctional components of modern, salt-free shampoo formulations with confirmed natural origin. The performance activity studies of shampoos, containing C(n)DMPAB surfactants, as well as model formulation (with commercial cocoamidopropyl betaine), included organoleptic and foaming characteristics, viscosity measurements, dispersibility in distilled and tap water as well as microbiological characteristics. Our studies showed great potential of novel C(n)DMPAB surfactants in replacing commercial cocoamidopropyl betaine, especially considering their increased viscosity, faster dispersibility as well as enhanced natural origin content.