The Synthesis And Properties Of Cleavable Cationic Gemini Surfactants

Cationic gemini surfactants have broad application prospects in the fields of sterilization,textile,wood preservation,metal corrosion inhibition,oil recovery and other fields attribute to their lower critical micelle concentration（CMC）,special aggregation ability and rheological properties.However,surfactants will accumulate in the environment during use,which can cause soil and water pollution.Especially,the cationic gemini surfactants have strong biological toxicity to aquatic organisms due to their strong bactericidal properties.In order to obtain more excellent and more environmentally friendly cationic gemini surfactants,amide and ester groups were introduced into the surfactant molecules,and two series of twelve new cationic gemini surfactants with cleavable properties were obtained.The specific research process is as follows:1.Three cationic gemini surfactants containing amide group in the spacer were synthesized through a two-step reaction,and their general chemical formula is:12),named BQA-n（n=8,10,12）.The structures of intermediate products and gemini surfactants were confirmed by Fourier transform infrared spectroscopy（FT-IR）and nuclear magnetic resonance hydrogen spectroscopy（¹H NMR）.2.The CMC of BQA-n（n=8,10,12）at different temperatures were determined by conductivity method.Compared with traditional monomer surfactants,these gemini surfactants have lower CMC.The counter ion dissociation degrees（α）and micellization standard Gibbs free energy(ΔG⁰_mic)of these gemini surfactants were calculated,and their Krafft temperatures（K_t）were determined.The results show that all of the three gemini surfactants have the ability to form micelles spontaneously and have good water solubility.3.Nine cationic gemini surfactants with amide group in the spacer and ester group in the hydrophobic chain were synthesized through a three-step reaction,and theirCONH-（CH₂）₃-N⁺（CH₃）₂CH₂COOC_nH_2n+1（m=2、3、4,n=8、10、12）,named BEQA-n,PEQA-n and HEQA-n（n=8,10,12）.The structures of intermediate products and gemini surfactants were confirmed by FT-IR and ¹H NMR.4.The CMC of BEQA-n,PEQA-n and HEQA-n（n=8,10,12）at different temperatures were determined by conductivity method.It was found that the simultaneous introduction of amide and ester groups makes the gemini surfactants have lower CMC.TheαandΔG⁰_mic of these gemini surfactants were calculated,and their Krafft temperatures（K_t）were determined.It showed that these gemini surfactants also have the ability to form micelles spontaneously and have good water solubility.The hydrolysis time of BEQA-n,PEQA-n and HEQA-n（n=8,10,12）in acidic and alkaline solutions was investigated.It was found that the simultaneous introduction of amide and ester groups made gemini surfactants have better hydrolysis ability.Ultraviolet-visible spectrophotometer,dynamic light scattering（DLS）,electron transmission microscope（TEM）and contact angle measurement were used to investigate the electrolyte tolerance,aggregation,wetting and foaming properties of the gemini surfactants containing both amide and ester groups.The results showed that both the length of the hydrophobic chain and the spacer of the gemini surfactants had a great influence on their surface properties,and the introduction of amide and ester groups also caused the gemini surfactant to change these properties.In addition,the minimum inhibitory concentrations（MIC）of BEQA-n,PEQA-n and HEQA-n（n=8,10,12）against E.coli ATCC 25922 and S.aureus ATCC 25923 were determined and used to evaluate the antibacterial activity of these gemini surfactants.HEQA-10 showed the best antibacterial activity against both strains.