Taken Metal Ion As Spacer To Form Gemini-type Surfactant Through Coordination Bond

Gemini surfactants are made of two amphiphilic moieties connected at the level of the head groups or very close to the head groups by a spacer group. Generally, Gemini surfactants are linked by common covalent bond and the space group has several atoms. In this thesis, Gemini-type surfactants through coordination bond by linking two conventional surfactants were studied, which took a single metal ion as "spacer". Two kinds of conventional surfactant C₁₂H₂₅N(CH₂COONa)₂ and C₁₂H₂₅NHCH₂COO--Na were synthesized and studied. Our work focused on the research of surface tension, pH and the effect of 2Na-EDTA. We confirmed that Gemini-type surfactants through coordination bond were formed. And we studied the effect of different metal ions , surfactants and pH et al. on the formation of Gemini-type surfactant. In aqueous solution C₁₂H₂₅N(CH₂COONa)₂ and C₁₂H₂₅NHCH₂COONa are mostly in the form of C₁₂H₂₅N⁺H(CH₂COO^-)₂ and C₁₂H₂₅NH₂⁺CH₂COO^-, respectively. Both forms have chelating ability. In their aqueous solution, a remarkable decrease of surface tension can be observed when divalent metal ion was added into the solution of C₁₂H₂₅N(CH₂COONa)₂ and C₁₂H₂₅NHCH₂COONa , respectively, in the mole ratio of 1:2 between metal ion and conventional surfactant. This indicated that Gemini surfactants may be formed. Variation of pH leads to the change of surface tension of surfactant with metal ion aqueous solution. The surface tension would increase with the decrease of pH. This is because surfactants would be protonated in acid aqueous solution and have no chelating ability. The more acid environment, the less Gemini-type surfactants would be formed. Different metal ions have different contribution to the decrease of surface tension. The better chelating ability of metal ion with surfactant could leads to lower surface tension of aqueous solution. Fe²⁺, Cu²⁺ and Ni²⁺ have better chelating ability than Zn²⁺, Mn²⁺ and so on, which leads to forming more Gemini-type surfactants and lower surface tension in aqueous solution, The chelating ability of conventional surfactant has great effect on the formation of Gemini-type surfactant through coordination bond. Surfactants with better chelating are easier to form into Gemini-type surfactant. C12H25N(CH2COONa)2 has better chelating ability than C12H25NHCH2COONa and C11H23COONa has almost no binding ability. The increase of surface tension was observed when 2Na-EDTA with the same mole as metal ion was added into the solution of C12H25N(CH2COONa)2 or C12H25NHCH2COONa with metal ion. This is because 2Na-EDTA has great binding ability with metal ion and leads to the collapse of Gemini-type surfactant.