Surface tension and micellization properties of heterogemini surfactants containing quaternary ammonium salt and sulfobetaine moiety.

A novel gemini surfactant with two hydrocarbon chains and two different hydrophilic parts containing a quaternary ammonium salt and a sulfobetaine moiety, N,N-dimethyl-N-{2-[N'-methyl-N'-(3-sulfopropyl)-alkylammonium]ethyl}-1-alkylammonium bromides (2C(n)AmSb, where n represents hydrocarbon chain lengths of 8, 10, 12, and 14), was synthesized by reacting N,N,N'-trimethylethylenediamine with n-alkyl bromide, followed by reacting with 1,3-propane sultone. The adsorption and aggregation properties of 2C(n)AmSb in the absence and presence of NaCl were characterized by the measurement of surface tension, steady-state fluorescence, and dynamic light scattering. The critical micelle concentration (cmc) and surface tension at the cmc of 2C(n)AmSb were compared with those for the corresponding monomeric surfactants, their mixtures, and gemini surfactants. The poor solubility in water shown by 2C(n)AmSb was improved by the addition of NaCl. The cmc of 2C(n)AmSb in the presence of NaCl is lower than that in the absence of NaCl, and the surface tension is almost identical for both systems. The radius of the aggregates formed by 2C(n)AmSb in a solution containing NaCl is found to be 0.70+/-0.3, 2.5+/-0.7, 5.6+/-1.4, and 10.7+/-2.4 nm for n=8, 10, 12, and 14, respectively. The particle size increases with an increase in hydrocarbon chain length; in particular, relatively large aggregates are formed for n=12 and 14.