Synthesis,Self-assembly And Inhibition Performance Of Asymmetric Quaternary Gemini Surfactants And Their Polymers

Carbon steel,one of the critical structural materials in industrial applications,is widely used in petrochemical,hydroelectric power generation,automobile production,and pipeline transportation because of its low cost and excellent mechanical properties.However,corrosion of carbon steel has always been one of the most important problems in the industrial field,causing substantial economic losses,environmental pollution,and waste of resources every year.Adding quaternary ammonium surfactants is an effective and low-cost way to alleviate the corrosion of carbon steel.Although many synthetic quaternary ammonium surfactants have been used in industrial applications to mitigate erosion of carbon steel,problems such as low corrosion inhibition efficiency,unstable adsorption film and short corrosion resistance time still exist.Therefore,it is essential to develop efficient and stable quaternary ammonium salt surfactants for the corrosion protection of carbon steel in the industry.In this paper,low molecular weight asymmetric quaternary ammonium salt Gemini surfactant,photo-responsive asymmetric quaternary ammonium salt Gemini surfactant,and polymerized polyquaternary ammonium salt surfactant were designed and synthesized.Their surface activity and self-assembly behavior were studied,and their corrosion inhibition performance on carbon steel was evaluated.The main research contents and results are as follows:（1）A series of quaternary asymmetric Gemini surfactants（PKO 15-3（OH）-n,n=12,14,16）were synthesized using long alkyl chain tertiary amines,epichlorohydrin,and N-[3-（Dimethylamino）propyl]dodecanamide.The molecular structures were determined by FT-IR,¹H NMR,and elemental analysis.Compared to the structurally similar symmetrical Gemini surfactant（ADQ-n）,PKO 15-3（OH）-n had a lower critical micelle concentration and higher surface activity.The results of the conductivity method suggested that the micellization processes of PKO 15-3（OH）-n in water were spontaneous and exothermic.The results of critical accumulation parameters,DLS,and TEM studies demonstrated that surfactants with larger asymmetry tend to form vesicles in aqueous solutions.The inhibition performance of A3 carbon steel by PKO 15-3（OH）-n in 0.5 mol L^-1 HCl solution was investigated by weight loss method,polarization curves,and AC impedance.The results showed that the inhibition efficiency of PKO15-3（OH）-n increased with the increase of asymmetry.PKO 15-3（OH）-n had higher inhibition performance than symmetrical surfactants with similar structures.In addition,the inhibition efficiency of PKO 15-3（OH）-12 remained as high as 93.55%when the immersion time was extended from 4 h to 20 days,indicating that the adsorbed film formed by PKO 15-3（OH）-12 on the carbon steel surface has excellent stability.The reactive sites of PKO 15-3（OH）-n were investigated by quantum chemical calculations,and the results showed that the N and O atoms on the amide bond in the PKO 15-3（OH）-n molecule formed coordination bonds with the empty d orbitals of Fe atoms and produced chemisorption.The molecular dynamics simulations show that the PKO 15-3（OH）-n molecules were adsorbed on the carbon steel surface in a parallel manner.Combining the experimental data and molecular dynamics simulations,the adsorption model of the asymmetric quaternary Gemini surfactant on the carbon steel surface was further constructed.（2）Compared with surfactants with low molecular weight,polymer surfactants have a larger chemical modification space,stronger selectivity,higher adsorption film strength,and can show better application performance.In order to further improve the corrosion inhibition performance of surfactant and the stability of the adsorption membrane,the asymmetric quaternary ammonium Gemini surfactant was polymerized by the free radical polymerization reaction,and polyquaternary ammonium polymer surfactant was successfully synthesized,namely poly（DE-3（OH）-12）.The structure was characterized by ¹H NMR and GPC.The surface tension studies showed that the surface activity of poly（DE-3（OH）-12）decreased after polymerization but was better than that of polymeric surfactants reported in the literature.The results of DLS and TEM indicated that the poly（DE-3（OH）-12）molecules tended to form micelles in aqueous solutions.The results of the weight loss and electrochemical method suggested that the inhibition properties and the stability of the adsorption film have been greatly improved by polymerizing the asymmetric quaternary ammonium salt Gemini surfactant,and the protection time of carbon steel has been extended effectively.（3）The performance of PKO 15-3（OH）-n or poly（DE-3（OH）-12）is relatively single.The introduction of azobenzene groups not only increases the active sites of surfactants and improves their corrosion inhibition efficiency,but also broadens the application fields of Gemini surfactants.A series of photo-responsive asymmetric quaternary ammonium Gemini surfactants（AZO-3（OH）-n,n=12,14,16）were synthesized by introducing azobenzene group into hydrophobic alkyl chains via dehydration condensation and quaternization reaction,which having the unique physicochemical properties of asymmetric Gemini surfactants and the optical activity of azobenzene groups.The molecular structure was determined by ¹H NMR and elemental analysis.The results obtained from the surface tension methods showed that trans-AZO-3（OH）-n had higher surface activity compared with PKO 15-3（OH）-n containing the same asymmetry.In addition,the surface activity andГ_max were obviously reduced by the transformation of AZO-3（OH）-n from trans to cis conformation after UV light irradiation.The critical packing parameters,DLS,and TEM results showed that AZO-3（OH）-n molecules formed vesicles in an aqueous solution under visible light,and then the vesicles disappeared and reassembled into micelles after UV irradiation.In addition,the foam performance was related to the surface tension,and the UV light irradiation induced the transformation of AZO-3（OH）-n molecular structure from trans to cis,which reduced the surface tension of AZO-3（OH）-n and realized the mutual transformation of foaming and defoaming.The results of corrosion inhibition performance showed that the introduction of the azobenzene group enhanced the corrosion inhibition performance of AZO-3（OH）-n,which may be due to more active sites on the azobenzene group,such as benzene ring,nitrogen-nitrogen double bond,etc.（4）The polymeric surfactant(poly（DE-3（OH）-AZO）,containing light-responsive,asymmetric quaternary Gemini links,was synthesized by free radical homopolymerization reaction using 2-（Dimethylamino）ethyl acrylate,4-n-butyl-4’-carboxy-azobenzene,and epichlorohydrin as raw materials.The molecular was characterized by ¹H NMR and GPC.The results of the surface tension method showed that the surface activity of poly（DE-3（OH）-AZO）decreased when it changed from trans to cis.The DLS and TEM results suggested that the aggregate morphology changed from vesicles to small micelles after alternate irradiation with visible and UV light.The weight-loss and electrochemical studies indicated that the number of active sites of a single molecule increased after the Gemini surfactant polymerization;thus,the adsorbed film’s stability and inhibition performance significantly improved.The results of quantum chemical calculations and molecular dynamics simulations were consistent with the experimental results.In summary,different types of asymmetric quaternary ammonium Gemini surfactants were synthesized in this paper to achieve efficient and durable protection of A3 carbon steel based on the molecular structure of symmetrical quaternary ammonium Gemini surfactants.In addition,the introduction of the azobenzene group endowed the surfactant photo-responsiveness,further expanding the applications scope of Gemini surfactant,laying a theoretical foundation for the future development of more functional oligomerization and polymer surfactant...