Abstract: Influence of carbon chain length of counter-ion of didecyldimethylammonium carboxylate with separate carbon chain length (n=2,4,6,8,10,12) on its surface activity and application performance was explored via determination of surface activity as well as foaming performance,emulsifying performance and wetting performance of the quaternary ammonium salt.Results indicated that as the carbon chain length of the counter-ion increases gradually,the surface activity of the quaternary ammonium carboxylate increases gradually too;while its cmc declines gradually;its minimum surface tension (γcmc) declines firstly and rises afterward,achieving at a lowest value as the carbon chain length equivalents to n=10.Meanwhile,the efficacy for lowering the water surface tension of 20 mN/m (pc20) increases gradually;saturate adsorption (Гtotal) increases gradually;the area occupied by a single molecule of the surfactant (Am) decreases gradually.As the increase of the carbon chain length,both the foaming and emulsifying performance enhance firstly and decline afterward;while the wetting performance enhances.

Key words: didecyldimethylammonium carboxylate, carbon chain length, surface activity, application performance