Study On The Synthesis And Properties Of Carboxylate Surfactants With ?-substituted Groups

Carboxylate surfactants are widely applied in food,printing and dyeing,construction,tertiary oil recovery and other fields because of their abundance,mild and biodegradable properties.However,due to the poor water solubility of saturated long-chain carboxylate surfactants,their applications are still limited.In this thesis,two kinds of carboxylate surfactants with?-substituted groups were synthesized by using fatty acids as starting materials.The water solubility and other related aqueous properties were further investigated.The main contents are summarized as follows:1.With lauric acid,tetradecanoic acid,hexadecanoic acid,stearate acid and eicosanoic acid as raw materials,two series of carboxylate surfactants,sodium?-phenoxy carboxylates?abbreviated as C_n-ph-Na,n=12,14,16,18,20?and sodium?-?para?or meta?-?tert-butyl?phenoxy?carboxylates?abbreviated as C_n-p-?t-bu?ph-Na and C_n-m-?t-bu?ph-Na,n=12,14,16,respectively?,were synthesized through bromide reaction,esterification reaction,Williamson etherification and saponification reaction.At the same time,several sodium fatty acids?abbreviated as C_nNa,n=12,14,16,18,20?were also synthesized for comparison.And all the products were confirmed by ¹H NMR.2.The water solubility of surfactants C_nNa and C_n-ph-Na were obtained by turbidity and observation method,respectively.Among the series of C_nNa surfactants,C₁₂Na has the best water solubility,which is 27 mmol�L^-1.However,for surfactants C_n-ph-Na,the aqueous solubility are 1250 mmol�kg^-1,1110 mmol�kg^-1,800 mmol�kg^-1,670 mmol�kg^-1 and 100mmol�kg^-1,respectively,which is far higher than that of C_nNa.Powder X-ray diffraction?XRD?measurement was carried out to investigate the crystal structure of the two series surfactants.For surfactant C_n-ph-Na,due to the presence of phenoxyl group at the?position,there is a large gap between the parallel aligned alkyl chains of head-to-tail-arranged surfactants in the solid state,leading to weakened cohesive forces between the alkyl tails and thus improving the aqueous solubility of surfactants.3.Surface activity of C_n-ph-Na was measured by surface tension method and fluorescence probe method.Their cmc values are 4.81 mmol�L^-1,0.56 mmol�L^-1,0.036mmol�L^-1,0.0068 mmol�L^-1and 0.033 mmol�L^-1,respectively.The prescence of benzene ring increases the surfactants hydrophobicity,and thus improving the aggregation ability.What's more,stable Pickering emulsions can be obtained by hydrophobization-modifying Al₂O₃nanoparticles in-situ by surfactants C_n-ph-Na.With increasing concentrations,C₁₂-ph-Na and C₁₄-ph-Na were able to induce double phase inversion of emulsions in the presence of alumina nanoparticles due to their suitable hydrophobicity.In addition,solutions of C₁₆-ph-Na and C₁₈-ph-Na at high concentration are viscoelastic.4.The solubility,surface activity and emulsifying capacity of surfactants C_n-p-?t-bu?ph-Na and C_n-m-?t-bu?ph-Na were investigated through UV-Vis spectrophotometry,surface tension method and fluorescence probe method.These surfactants have good aqueous solubility,emulsifying ability and strong aggregation ability.Moreover,the viscoelasticity of surfactants solutions was studied through static and dynamic rheological measurements.C₁₂-p-?t-bu?ph-Na,C₁₄-p-?t-bu?ph-Na,C₁₄-m-?t-bu?ph-Na and C₁₆-m-?t-bu?ph-Na solutions can form viscoelastic solutions at relatively low concentrations.Cryo-TEM identified the presence of wormlike micelles in the solutions.