Synthesis and surface activities of a novel di-hydroxyl-sulfate-betaine-type zwitterionic gemini surfactants

A series of novel di-hydroxyl-sulfate-betaine-type zwitterionic gemini surfactants of 1,2-bis[N-ethyl-N-(2-hydroxyl-3-sulfopropyl)-alkylammonium] alkyl betaines (DBAs–n, where s and n represent the spacer length of 2, 4 and 6 and the hydrocarbon chain length of 8, 12, 14, 16 and 18, respectively) were synthesized by reacting alkylamine with sodium 3-chloro-2-hydroxypropanesulfonate (the alternative sulphonated agent), followed by the reactions with а,ω-dibromoalkyl and then ethyl bromide. Their adsorption and aggregation properties were investigated by means of equilibrium surface tension, dynamic light-scattering (DLS) and transmission electron microscopy (TEM). DBAs–n gemini surfactants showed excellent surface activities and packed tightly at the interface. For example, the minimum CMC value for DBAs–n series was of the order of 10−5 M and the surface tension of water can be decreased as low as 22.2 mN/m. It was also found that the aggregates of DBAs–n solutions were significantly dependent on their hydrocarbon chain lengths. The aggregates changed from vesicles to entangled fiber-like micelles as the chain length increased from dodecyl to tetradecyl.