Polymeric Surfactants in Supercritical Fluids

9626828约翰斯顿的目标是(1)将实验和理论结合起来，以提供对含有压缩二氧化碳的体系中表面活性剂对界面性质的影响的基本了解，以及(2)将这些表面活性剂用作空间稳定剂，通过沉淀成二氧化碳来形成尺寸均匀的聚合物微粒和微纤维。二氧化碳是一种环境友好的溶剂，正被用来取代有机溶剂，以最大限度地减少废物。在未来的材料形成和多相聚合过程中，表面活性剂将扮演重要的角色。由于二氧化碳的性质与亲水性或亲油性溶剂完全不同，因此将需要创新的新型表面活性剂。首次用新型串联式变体积张力计测量了液体与二氧化碳之间的界面张力和表面活性剂在这些界面上的吸附，并用一种新的晶格流体自洽场模型进行了计算。实验研究和模型将用于在分子水平上设计聚合物表面活性剂，以稳定CO2与不同极性的液体之间的界面，包括水、聚乙二醇齐聚体、聚丙烯酸酯和聚苯乙烯。用蒙特卡罗计算机模拟方法研究超临界流体对高分子链的溶剂化作用。具体地说，将确定从溶剂化链到塌陷链的转变，并采用接近较低临界溶液温度相边界的方法。上述基础知识将被用来设计表面活性剂，通过沉淀成液体和超临界流体二氧化碳来生产聚合物材料。在这里，聚合物溶液通过毛细管喷洒到二氧化碳中，以沉淀出尺寸小至100纳米的微粒、微球和微纤维。表面活性剂将在空间上稳定沉淀聚合物的微观结构，以最大限度地减少絮凝和团聚，这通常是当前技术的主要限制。界面性质在材料形成过程和多相聚合中起着关键作用。对于可溶于CO2的表面活性剂，表面活性剂的吸附尚未得到解决。界面张力和吸附影响许多现象，包括分散相的成核、生长、稳定和合并、喷雾的雾化以及从喷雾中形成纤维。了解表面活性剂在CO2液界面上的吸附将对这些现象的基础研究以及新材料的形成和聚合工艺的开发都大有裨益。***

9626828 Johnston The objectives are (1) to combine experiment and theory to provide a fundamental understanding of the effects of surfactants on interfacial properties in systems containing compresses carbon dioxide, and (2) to use these surfactants as steric stabilizers to form uniformly sized polymer microparticles and microfibers by precipitation into carbon dioxide. Carbon dioxide is an environmentally benign solvent that is being used to replace organic solvents for waste minimization. In future materials formation and heterogeneous polymerization processes, surfactants will play an important role. Because Co2 has very different properties than either hydrophilic or lipophilic solvents, innovative new types of surfactants will be required. The interfacial tension between liquids and carbon dioxide, and the adsorption of surfactants at these interfaces, will be measured with a novel tandem variable-volume tensionmeter for the first time and also calculated with a new lattice fluid self-consistent field model. The experimental studies and the model will be used to design polymeric surfactants at the molecular level to stabilize the interface between Co2 and liquids of varying polarity including water, and oligomers of poly(ethylene glycol), polyacrylates and polystyrene. The solvation of polymer chains by supercritical fluids will be studied by Monte Carlo computer simulation. Specifically, the transition from solvated chains to collapsed chains with the approach to a lower critical solution temperature phase boundary will be determined. The above fundamental knowledge will be used to design surfactants to produce polymeric materials by precipitation into liquid and supercritical fluid carbon dioxide. Here, a polymer solution is sprayed through a capillary into CO2 to precipitate microparticles, microspheres, and microfibers, with dimensions as small as 100nm. The surfactant will sterically stabilize the precipitating polymer microstructure to minimize flocculation and agg lomeration, which is often a major limitation in the current technology. Interfacial properties play a key role in materials formation processes and heterogeneous polymerizations. Surfactant adsorption has not yet been addresses for CO2 soluble surfactants. The interfacial tension and adsorption influence many phenomena including nucleation, growth, stability and coalescence of dispersed phases, atomization of sprays, and fiber formation from sprays. A knowledge of surfactant adsorption at CO2 liquid interfaces will be high beneficial to both fundamental studies of these phenomena and the development of new materials formation and polymerization processes. ***