Molecular-Based Study of Reversed Micelles in Supercritical in Carbon Dioxide for Solvent Substitution in the U.S. Chemical Industry

小行星9613555 建议使用小角X射线（SAXS）和中子（SANS）散射加上互补的分子动力学（MD）和蒙特卡罗（MC）模拟，以开发一个分子水平的理解的反胶束（RM）在超临界二氧化碳（SC-CO2）的形成和稳定性。 该项目的结果将有助于美国化学工业的基本知识基础，以取代目前大多数工业化学反应和分离过程中使用的许多有毒或有害溶剂。 尽管SC-CO2具有作为溶剂替代品的吸引力，但它并不是某些物质的良好溶剂，例如：1）水、水溶性和极性物质，或2）大多数高分子量物质，如合成聚合物或蛋白质。 然而，已经提出了通过使用RM在SC-CO2中处理这些不溶性物质的技术。 最近，经过十多年的研究，已经发现合适的表面活性剂可以将水溶液和聚合物分散在RM和SC-CO2中。 这项工作的目的是了解新发现的表面活性剂的详细分子特征如何有助于RM的形成，以了解是什么使成功的CO2 - 亲表面活性剂尾的研究，表征了连续SC-CO2相与微观RM核之间的界面层，为预测和测量RM的尺寸和形状奠定了基础，为SC-CO2中RM作为液体溶剂的替代物的广泛工业应用提供了所需的知识基础。 建议应用四种基于分子的技术来研究SC-CO2中的RM：1）SANS，因为其能够通过选择性氘化来改变特定分子组分之间的对比度，2）SAXS，因为其高生产率和与SANS相比的不同对比度，3）MC，因为其有效探索构型空间，以及4）MD，因为其能够在分子水平上探索动力学过程。 散射可以告诉很多关于微观结构（球体？棒？薄板？生物连续结构？）宏观结构（集群？）无法通过其他方式获得的RM。ORNL的30米SANS仪器和现有的高压SAXS单元将用于表征聚合物和水岩心的RM。 ORNL的大规模并行Intel Paragon超级计算机将用于使用从OPLS参数集开发的精确模型来模拟SC-CO2中新发现的表面活性剂的RM。 Paragon超级计算机的功率和我们的并行技术的效率的组合将允许确定预构造的RM的稳定性。一个主要的目标将是作出定量比较稳定的RM结构确定SANS和SAXS实验和模拟确定的。 然后，它建议使用模拟实验，与现有的热力学数据，以了解平衡的相互作用，需要形成稳定的RM在SC-CO2，从而了解成功的表面活性剂所需的分子结构。 随着SANS、SAXS、MC和MD研究的预期成功，将提供一套完整的基于分子的工具来研究SC-CO2中的RM。 利用这些工具，提出了测试和调整现有的含水RM的热力学模型，例如，那些Nagarajan，Blankschtein和Holland，在SC-CO2中的RM。 分子和热力学模型，它建议建议新的表面活性剂的合成和测试。 即使是实现这种程度的成功的一小部分，也将大大增强SC-CO2在美国化学工业中广泛替代传统液体溶剂的知识基础。 最终结果将是一个更有竞争力的行业，减少排放。 ***

9613555 Cummings It is proposed to use small angle x-ray (SAXS) and neutron (SANS) scattering plus complementary molecular dynamics (MD) and Monte Carlo (MC) simulations to develop a molecular-level understanding of the formation and stability of reverse micelles (RMs) in supercritical carbon dioxide (SC-CO2). The results of this project will contribute to the fundamental knowledge base for the U.S. chemical industry to substitute SC-CO2 for many of the toxic or hazardous solvents presently used in most industrial chemical reaction and separation processes. Despite its attractive features as a solvent substitute, SC-CO2 is not a good solvent for certain classes of substances, e.g. 1) water, water-soluble, and polar substances or 2) most high molecular weight substances such as synthetic polymers or proteins. Techniques have been proposed, however, for processing these insoluble substances in SC-CO2 through the use of RMs. Recently, after a decade-long search, appropriate surfactants have been discovered to disperse both aqueous systems and polymers in RMs andSC-CO2. The aim of this work is to understand how the detailed molecular characteristics of the newly discovered surfactants contribute to the formation of RMs to understand what makes a successful CO2 -philic surfactant tail, to characterize the interfacial layer between the continuous SC-CO2 phase and the microscopic RM core, to establish the basis for predicting and measuring the size and shape of RMs, in short, to provide the molecular foundations for the needed knowledge base for widespread industrial utilization RMs in SC-CO2 as substitute for liquid solvents. It is proposed to apply four molecular-based techniques to study RMs in SC-CO2: 1) SANS for its ability to vary contrast between specific molecular components through selective deuteration, 2) SAXS for its high productivity and different contrast compared with SANS, 3) MC for its efficient exploration of the configuration space, and 4) MD for its capability to explore dynamical processes at a molecular level. Scattering can tell much about the microstructure (spheres? rods? lamella? biocontinuous structures?) and macrostructure (clustering?) of RMs which is unavailable by other means. Both the 30-m SANS instrument at ORNL with the existing high pressure SAXS cell, will be used to characterize RMs with both polymer and water cores. And the massively parallel Intel Paragon supercomputers at ORNL, will be used to simulate RMs from the newly discovered surfactants in SC-CO2 using accurate models developed from the OPLS parameter set. The combination of the power of the Paragon supercomputers and the efficiency of our parallel techniques will permit determination of the stability of preconstructed RMs. A primary goal will be to make quantitative comparisons between the stable RM structures as determined by SANS and SAXS experiments and those determined by simulation. Then, it is proposed to use simulation experiments, with available thermodynamic data, to understand the balance of interactions that is required to form stable RMs in SC-CO2, and thus to understand the molecular structure required for a successful surfactant. With anticipated success in the proposed SANS, SAXS, MC, and MD studies, a full repertoire of molecular-based tools for study of RMs in SC-CO2 would be available. With these tools it is proposed to test and adapt existing thermodynamic models of aqueous RMs, e.g., those Nagarajan, Blankschtein, and Holland, to RMs in SC-CO2 . With both molecular and thermodynamic models, it is proposed to suggest novel surfactants for synthesis and testing. Achieving even a small fraction of this degree of success, will substantially enhance the knowledge base for widespread substitution of SC-CO2 to replace conventional liquid solvents in the U.S. chemical industry. A more competitive industry with reduced emissions will be the ultimate result. ***