Aggregation Behavior Of Quaternary Ammonium Gemini Surfactants With Oligo(Oxyethylene) Spacer In Heptane Solution

Quaternary ammonium Gemini surfactants are made up of two cationic surfactants connected at the lever of the head groups by a hydrophilic spacer chain. The distance between the head groups in Gemini molecule can be controlled through designing and synthesizing different length of the spacer chain. This results in changes in the molecule geometry and the alkyl chain density of the surfactant molecule, and also in the charge density of ionic head groups and their hydration. All these changes would directly affect the self-association of surfactant molecules and the structure of aggregate. At present, the study of oligo(oxyethylene) alkanediyl -α,ω-bis- dimethylalkyl-ammonium bromide only focused on the self-association rule of Gemini surfactant molecules in the aqueous solution, few studies are concentrated on the nonaqueous system.So the aggregation behavior of Gemini surfactants C₁₂-EO_x-C₁₂·2Br(x=1,2,3) in heptane had been investigated systematically. The dissolution of C₁₂-EO_x-C₁₂·2Br in heptane needs n-hexanol as cosolvent, so we studied the reverse micelle properties and the structure of Gemini surfactants in n-hexanol/n-heptane at fixed volume rate of 0.2. And the critical reverse micelle concentrations (crmcI) of C₁₂-EO_x-C₁₂·2Br in heptane solutions had been investigated by absorption spectrum method using iodine as probe. The saturated amount of water solubilization in the reverse micelles was measured by water solubilizing method. Finally the W/O microemulsions of C₁₂-EO_x-C₁₂·2Br had also been investigated by the dilution method, including the influence factors of water content W₀ and the spacer chain x. The main results are concluded as follows:1. The critical reverse micelle concentrations crmcI of C₁₂-EO_x-C₁₂·2Br using iodine probe spectrometric method has been found to increase with increasing x, which is similar to the variation of the critical micelle concentrations cmcaq with x in the aqueous solution.2. The results of water solubilizing method indicates that the saturated amount of water in C₁₂-EO_x-C₁₂·2Br/heptane/hexanol systems enhances with increasing x and increasing temperature.