| Studies have shown that Gemini surfactants were a new type of surfactants with two single chain amphiphiles linked at hydrophilic head group by the spacer.The properties of Gemini surfactants vary greatly with each other due to the difference in the spacer.In this paper,by designing the molecular structure,a new type of amide Gemini anionic surfactants with rigid group as the spacer were synthesized and characterized,namely,N,N-bis-dodecyl-2,6-pyridinium dimethylamide propionate sodium,N,N-bis-tetradecyl-2,6-pyridinium dimethylamide propionate sodium and N,N-bis-hexadecyl-2,6-pyridinium dimethylamide propionate sodium?abbreviated as DLP-12,DLP-14,DLP-16?,their surface chemical properties,hydrodynamic radius as well as potential applications were explored.The details are as follows:?1?2,6-pyridyldiformyl chloride and N-alkyl-?-amino propionic acid methyl ester were obtained through two steps of chemical reaction.The amide Gemini anionic surfactants with hydrophobic chain of 12,14 and 16 were synthesized by amidation and saponification.The optimal conditions for the reaction were explored by single factor experiments.When reaction temperature was 40°C,reaction time was 8 h and n?N-dodecyl-?-amino propionic acid methyl ester?:n?2,6-pyridyldiformyl chloride?was 2.4:1,the yield of DLP-12 was 68.14%.?2?The properties of DLP were determined.The results showed that they performed good emulsifying property,foam property and solubilization ability,which enhanced with the increase in hydrophobic chain.However,the wettability and solubility showed the opposite rules.The critical micelle concentration?cmc?of DLP was determined by three methods,including surface tension,conductivity and steady-state fluorescence method.The difference between the cmc values measured by the three methods was little and the change rules were consistent.With the increase in the hydrophobic chain,the cmc decreased.The cmc determined by surface tension were 9.091×10-5 mol/L,7.940×10-5 mol/L and 5.984×10-5 mol/L for the DLP-12,DLP-14,DLP-16 at the temperature of 298.15 K,respectively,which were much lower than the traditional single chain amphiphilic monomer used in the experiment.For the same surfactant,with the increase in temperature,surface tension at critical micelle concentration(?cmc)decreased,while cmc increased.The calculation results of micellization thermodynamic parameters showed that the process of micelle association was exothermic and spontaneous.The packing parameters?P?for DLP-12,DLP-14 and DLP-16 were 0.644,0.444 and 0.405under the same conditions which showed that DLP-12 was easy to form layer-like structure or vesicle in solution,DLP-14 was easy to form short rod-like structure and DLP-16 was easy to form long rod-like or vesicle structure.The results of dynamic light scattering?DLS?showed that with the increase in the hydrophobic chain,the hydrodynamics radius increased.The results of dynamic light scattering?DLS?showed that the hydrodynamic radius of surfactant increased with the increase in hydrophobic chain.The results of TGA showed that the initial decomposition temperatures of DLP-12,DLP-14 and DLP-16 were far more than 80°C,therefore,it was expected to be applied in the field of oil exploitation.?3?The interaction between anionic Gemini surfactant and cationic dye methylene blue?MB?was studied.The results showed that MB and DLP-12 could interact with each other due to the electrostatic interaction.On the one hand,NaCl could promote the formation of surfactant micelles,on the other hand,due to the existence of coexisting ions,the ion charge between MB and DLP-12 was shielded to a certain extent;While,hydroxypropyl-?-cyclodextrin?HP-?-CD?could entangle with the hydrophobic chain of surfactant through hydrophobic action,resulting in the change of corresponding absorption spectrum. |
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