Stabilization Mechanism of Emulsions and Latexes in CO2

我们的目标是在压缩的基于二氧化碳的体系中发展胶体和界面科学的知识，以便为稳定的(1)有机聚合物乳液和(2)由水和二氧化碳组成的乳液设计表面活性剂。表面活性剂在有机-二氧化碳和水-二氧化碳界面上的吸附将被描述为表面活性剂的“亲二氧化碳”和“厌恶二氧化碳”部分之间的平衡的函数。同时，乳胶和乳液的空间稳定性将通过改变表面活性剂的亲二氧化碳部分的溶剂化长度和程度来控制。将界面性质和胶体稳定性与表面活性剂结构联系起来，对于合理设计CO2中这些新型胶体的表面活性剂是至关重要的。将开发新型的二嵌段或三嵌段共聚物表面活性剂结构，以稳定CO2中的有机聚合物乳液，然后将其转移到水中形成稳定的水性乳液。在二氧化碳中，表面活性剂的亲二氧化碳链段将提供空间稳定。一旦转移到水中，这一段将坍塌到表面，另一段将电离以提供静电稳定。胶乳的稳定性将与表面活性剂在二氧化碳和水中的吸附、胶乳颗粒大小、二氧化碳密度和(在水中)表面电荷(在水中)作为pH的函数有关，将发展对表面活性剂在二氧化碳中水界面的性质的知识，以指导对二氧化碳中水(W/C)和水中二氧化碳(C/W)乳状液稳定性的研究。通过对界面张力的测量，可以确定表面活性剂的“亲二氧化碳”和“憎二氧化碳”或亲水部分的平衡点。这一平衡状态将作为理解乳状液稳定性和类型(曲率)(W/C或C/W)作为表面活性剂结构、压力、温度和盐度的函数的重要参照点。由水和二氧化碳组成的乳液可用于无溶剂涂料、生物分子的反应和分离、多相聚合、提高石油采收率、形成高比表面积材料，以及清洗金属、织物、半导体和受污染的土壤。考虑到全球每年使用的有机溶剂超过300亿磅，减少废物的潜力是巨大的。

ABSTRACTCTS-9905531Johnston, Keith P.U. of Texas @ AustinThe objective is to develop a knowledge of colloid and interface science in compressed CO2-based systems in order to design surfactant for stable (1) organic polymer latexes and (2) emulsions composed of water and CO2. The adsorption of surfactant at organic-CO2 and water- CO2 interfaces will be described as a function of the balance between the surfactant's "CO2-philic" and "CO2-phobic" segments. Simultaneously, steric stabilization of latexes and emulsions will be controlled by varying the length and degree of solvation of the CO2-philic segment of the surfactant. The ability to relate interfacial properties and colloid stability to surfactant structure is of vital importance for the rational design of surfactants for these novel colloids in CO2.Novel types of diblock or triblock copolymer surfactant structure will be develop to stabilize an organic polymer latex in CO2, which can then be transferred to water form a stable aqueous latex. In CO2, the CO2-philic segment of the surfactant will provide steric stabilization. Upon transfer to water, this segment will collapse onto the surface, and another segment will ionize to provide electrostatic stabilization. The stability of the latex will be related to the adsorption of the surfactant in CO2 and water, the latex particle size, the CO2 density and the surface charge (in water) as a function of pH.A knowledge of the properties of surfactants at the water-in-CO2 interface will be developed to guide studies of the stability of water-in-CO2 (W/C) and CO2-in-water (C/W) emulsions. From measurements of the interfacial tension, the point where the "CO2-philic" and "CO2-phobic" or hydrophilic parts of the surfactant are balanced will be identified. This balance state will serve as crucial reference point to understand emulsion stability and type (curvature) (W/C or C/W) as a function of surfactant structure, pressure, temperature and salinity. Novel sub-micron emulsions will be formed where the interfacial tension is very low, and then the pressure or temperature will be adjusted to manipulate the stability of the emulsion.Emulsions composed of water and CO2 may be utilized for solvent-free coatings, reactions and separations of biomolecules, heterogeneous polymerization, enhanced oil recovery, formation of high surface area material, and cleaning of metals, fabrics, semiconductors, and contaminated soil. The potential for waste reduction is enormous given that more than 30 billion pounds of organic solvents are used worldwide each year.