Abstract: A quaternary ammonium Gemini surfactant (14-8-14) was synthesized from N,N-dimethyl tetradecylamine and 1,8-dibromooctane.The optimum reaction condition was obtained by single factor experiment.The optimum synthesis condition was as follows:the dosage of N,N-dimethyl amine was 5 mmol;the molar ratio of n(N,N-dimethyl amine)∶n(dibromoalkane) was 2.2∶1;10 mL acetonitrile was used as solvent;the reaction temperature was 80 ℃;and the reaction time was 24 h.24 kinds of quaternary ammonium Gemini surfactants m-n-m were synthesized under this condition,most of which had a yield larger than 80%.The surface tension of the products were determined.The effects of the hydrophobic alkyl chain and the spacer on the surface activity of Gemini surfactants were studied.The results show that,for the same spacer n,the surface tension of Gemini surfactants first decreases and then increases with the increase of hydrophobic alkyl chain length (m>10).14-n-14 Gemini surfactants exhibit the best surface activity.Moreover,when the hydrophobic alkyl chain m=14,the surface tension of Gemini surfactants first increases and then decreases with the increase of the spacer length n.

Key words: Gemini surfactant, bis-quaternary ammonium salt, synthesis, surface activity