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 (DBA s – 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). DBA s – n gemini surfactants showed excellent surface activities and packed tightly at the interface. For example, the minimum CMC value for DBA s – 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 DBA s – 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.