Synthesis And Surface-active Properties Of Novel Cationic Gemini Surfactants

In recent years,new types of surfactant called Gemini surfactants have attracted increasing attention of various industrial and academic research groups.Gemini surfactants are a new class of surfactants having two hydrophobic tails and two hydrophilic head groups connected through a linkage adjacent to the hydrophilic head groups in a molecule.They display greater propensity to form micelles and can efficiently reduce surface tension compared with their corresponding conventional single-chain surfactants counterparts.In this dissertation,three series of quaternary-ammonium Gemini surfactants were designed and synthesized by a three-step synthetic sequence:substitution reaction,ammoniation reaction and quaternization reaction.The target compounds were synthesized by using long chain 1-bromohydrocarbons(1-bromoctane, 1-bromodecane,1-bromododecane,1-bromotetradecane,1-bromohexadecane), dihydric alcohol compounds(ethylene glycol,diethylene glycol,triethylene glycol ether),epichlorohydrin and dimethylamine as starting materials.First,three diepoxy-compounds(ethylene glycol diglycidyl ether 4a,diethylene glycol diglycidyl ether 4b,diglycidyltriethylene glycol 4c) were synthesized from epichlorohydrin and dihydric alcohol compounds.Then another series of important intermediates (bis[dimethylaminomethyl]triethylene glycol 5a,bis[dimethylaminomethyl]-tetraethylene glycol 5b,bis[dimethylaminomethyl]pentaethylene glycol 5c) were synthesized.These amination products were used in the next quaternization reaction step to synthesize three series of quaternary-ammounium Gemini surfactants.All new products were characterized by IR spectra,¹H NMR spectra,¹³C NMR spectra and MS. The surface properties including surface excess concentration,Γ_cmc,surface area demand per molecule,A_cmc,efficiency in surface tension reduction,pC₂₀,the effectiveness of surface tension reduction,γ_cmc,critical micelle concentration,CMC, and standard free energy of micellization,ΔG_ads⁰ andΔG_mic⁰,were investigated by means of surface tension measurements.The relationship between the structure and properties was discussed.The results showed that compared with those of its corresponding conventional single-chain surfactants,these novel Gemini surfactants had lower critical micelle concentration and reduced surface tension more efficiently. The foaming properties of the synthesized Gemini surfactants were also studied.The results showed that the foaming ability of these Gemini surfactants decreased with the increase of the length of alkyl chain in the cationic Gemini surfactants.