Hypothesis: Surface activity of selected cleavable esterquat cationic surfactants is determined by the synergistic effect of surface active products of their hydrolysis.
Experiments: Interfacial behavior of two classes of esterquat surfactants, quaternary alkylammmoniumesters and amino acid betaine (trimethylglycine) esters of fatty acids were examined both experimentally and theoretically. The surface tension measurements at air/water interface were performed by the pendant drop shape analysis method, then the obtained isotherms were theoretically described by the model of adsorption of ionic/non-ionic surfactants mixtures taking into account the presence of surface active products of surfactant hydrolysis.
Findings: We found that surface activity of the mixture of surface active compounds resulting from the esterquat basic hydrolysis increases with time and it is higher when the ester carbonyl group is connected with the quaternary amine by bridging oxygen than in the inverted (betaine ester type) arrangement. That is, in the first case, the consequence of strong synergistic effect between the cationic esterquat surfactant and the anionic product of its hydrolysis - dodecanoate ion, while in the second case, the non-ionic hydrolysis product - dodecanol exhibits much weaker synergy. The addition of side CH3 group into the esterquat head-group slows down the hydrolysis that leads to the lower surface activity of the resulting mixture.
Keywords: Adsorption; Cationic amphiphiles; Cleavable surfactants; Esterquats; Hydrolysis; Water/air interface.
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