Effect of salt counterions on the physicochemical characteristics of novel green surfactant, ethane-1,2-diylbis(N,N-dimethyl-N-tetradecylammoniumacetoxy) dichloride

In this research article we have examined the effect of chloride (Cl-), sulphate (SO42-), phosphate (PO43-), anthranilate (An(-)) and tosylate (Tos(-)) counterions on the physicochemical characteristics of green gemini surfactant, ethane-1,2-diyl bis(N,N-dimethyl-N-tetradecylammoniumacetoxy) dichloride (14-E2-14) through a multidimensional approach. Substantial changes were observed in the physicochemical parameters. Counterions were found to cause reduction in critical micellar concentration (CMC) and minimum area per head group (A(min)) of the 14-E2-14 gemini surfactant. However, increase in aggregation number (N-g) and surface excess concentration (Gamma(max)) of the 14-E2-14 surfactant was observed upon increasing the counterion concentrations. The Gibbs free energies of micellization (Delta G(mic)(o)) and adsorption (Delta G(ads)(o)) ads, were found to be negative, indicating that 14-E2-14 micellization is spontaneous. The order of efficacy of counterions to influence the micellar characteristics was: An(-) > Tos(-) > PO43- > SO42- > Cl-. Further, H-1 NMR results demonstrated morphological transitions (sphere-to-rod) and newer phase formation. The UV-vis and FT-IR results delineate intercalation of organic counterions (An(-) and Tos(-)) into the palisade layer of 14-E2-14 micelles. TEM micrographs show emergence of non-spheroidal micelles at higher counterion concentrations. This study could be significant to surfactant science scientists in tailoring green surfactants with desirable physicochemical characteristics, so that special-characteristic-tailored surfactants could be exploited in designing and compilation of environmentally benign industrial, cosmetic and biomedical products. (C) 2016 Elsevier B.V. All rights reserved.