碳氢表面活性剂的设计、合成及其构建水/CO2微乳液的作用机理

Water-in-CO2 (w/c) microemulsions, formed by fluorinated surfactants and a very few hydrocarbon surfactants, has been widely accepted as a promising approach to overcome the disadvantage of CO2 as a very poor solvent for those polar and high molecular weight solutes. However, high cost and toxicity of the fluorinated surfactants, and extremely high pressures and low water content of w/c microemulsions established by the hydrocarbon surfactants make the w/c microemulsions incapable for practical application in large scale. In this project, molecular simulations combined with controllable polymerization will be used to design and synthesize hydrocarbon surfactants. The mechanism of the surfactants forming w/c microemulsions will be studied. The phase behavior and surface tension of the surfactants will be measured in high pressure CO2, and the interactions between the surfactants and CO2 will be investigated by using molecular simulations. Then, the unit group of the surfactants which can form w/c microemulsions will be screened. Compared with the characterization results of high-pressure in situ UV-Vis spectra, small angle neutron scattering and small angle x-ray scattering on the w/c microemulsions, a modeling of micelle of the microemulsions for calculating the boundary layer density will be established to discover the effect of structures on the boundary layer density including the ratio of CO2-philic group to water-philic group and single or double tails in the hydrocarbon surfactants. The results may obtain the principles for designing the hydrocarbon surfactants which can form the w/c microemulsions and the methods for manipulating the structure and properties of the w/c microemulsions.

含氟表面活性剂或极少数碳氢表面活性剂可用于构建水/CO2微乳液，克服因CO2非极性无法溶解大分子和极性物质的缺陷，但前者价格昂贵、有毒，而后者所需压力极高且构建的微乳液含水量少，使得水/CO2微乳液至今无法获得大规模实际应用。本项目拟采用分子模拟结合实验研究的方法，利用活性可控聚合手段设计、合成碳氢表面活性剂，探索其构建水/CO2微乳液的作用机理。通过实验测定合成表面活性剂在构建微乳液时的相行为、界面张力，并采用分子模拟分析其与CO2的相互作用，筛选可用于构建微乳液的表面活性剂结构单元。通过高压原位紫外光谱、小角中子散射、小角X射线散射等表征手段，考察不同结构（包括亲水/CO2基团比例、单双尾链等）表面活性剂构建的微乳液的微观结构，建立可靠的微乳液分子模拟方法，确定碳氢表面活性剂结构在微乳液构建过程中对边界层密度影响的作用机理，获得碳氢表面活性剂的设计准则，掌握对微乳液结构性能的调控手段。

CO2具有无毒、不燃、价廉及超临界条件温和等优点，但其非极性无法溶解大分子和极性物质限制了其应用范围。W/C微乳液的构建可解决该难题，但目前能最有效形成W/C微乳液的含氟表面活性剂价格昂贵且对环境不利，使W/C微乳液无法得到广泛应用。研究设计合成污染小、成本低廉的碳氢类（助）表面活性剂构建W/C微乳液是实现其实际应用的关键。本项目通过分子动力学模拟与实验相结合的方法，设计合成系列具有不同支链化程度的碳氢类表面活性剂，探索支链化结构与CO2相互作用机理；制备了不同支链化程度的非氟助表面活性剂协助含氟表面活性剂构建W/C微乳液，通过实验测定微乳液微水环境，并采用模拟分析（助）表面活性剂对微乳液结构性能的影响；建立了可靠的微乳液分子模拟方法并模拟研究表面活性剂的双尾链结构对微乳液界面行为的作用机制；使用多元组分构建C/W乳液并通过实验及耗散力子动力学模拟对其稳定性进行分析；对可用于含重金属和多环芳烃土壤修复的W/C微乳液构建原则进行探索，研究结果可为低/非氟含量W/C微乳液的构建与应用提供新途径和新机制。