Studies on Fluids and Fluid Mixtures: Connecting Theory with Experiment

这笔赠款由材料研究部和化学部共同资助。这项研究的目标是将流体及其混合物的微观结构和宏观行为联系起来，特别是对复杂的流体。虽然研究工具是理论上的，但重点是与实验建立联系，并在适当的情况下与模拟联系起来。这项工作提供的一个不同寻常的机会是，能够使用相同的理论方法比较晶格模型和连续模型的结果。复杂流体的行为最近引起了人们的高度兴趣，这是因为科学家可以获得越来越复杂的测量类型，以及模拟稠密流体混合物的能力大大扩展。本文提出的研究建立在PI和她的团队使用Born-Green-Yvon(BGY)积分方程法模拟晶格和连续介质流体和混合物的工作基础上。晶格理论给出了简单的热力学变量的封闭表达式。它的优势包括它对非理论家的可及性，以及使用复杂系统上的晶格模拟结果来测试它的能力。连续统理论能够处理更微妙的问题，涉及局部结构和整体性质之间的相互作用。然而，需要数值方法，而且对混合物的模拟数据有限。类似的晶格和连续统理论的发展为确定哪些性质对施加晶格约束敏感创造了机会。这里提出的晶格研究集中在三个项目上：重新推导BGY理论来描述薄膜和界面，并研究向块体的转变；增加所研究的体系的复杂性，以包括三元混合物；以及将BGY理论的热力学结果映射到Flory-Huggins chi参数的形式上，Flory-Huggins chi参数是聚合物社区中最广泛使用的特征参数。这项工作将建立在格子BGY理论描述简单和聚合物流体和混合物的已证明的能力的基础上，并将利用最近开发的从最少的实验数据中提取大量信息的策略。在连续介质方面，BGY理论最近被用于研究高达16-MERS和正构烷烃的方井流体。这些结果将为拟议的小支链烷烃研究提供信息，该项目将导致更好地理解填充对流体性质的影响，并因此了解当使用晶格BGY理论时可能丢失的内容。第二个项目专注于短链流体的方井混合物；组分将在单体和8-MERS之间变化，从而扩大了当前模拟结果的限制。这项研究将需要考虑分子间和分子内分布的浓度依赖性：如何处理它，以及在什么条件下它将变得重要。在这项工作中，实验数据/分析与PI开发的用于研究复杂流体的理论工具之间的联系将得到扩展和加强。其结果是，材料社区可以使用更复杂的策略组合来解决与理解微观结构和宏观行为之间的联系有关的问题。本科生和研究生的本地演讲将帮助他们发展教学技能。结果还将通过国际和平协会及其研究小组在全国会议和出版物上所作的会议发言来传播。国际和平研究所在研究和教学指导方面的努力已导致研究生和研究生队伍中的妇女人数以及教员中的妇女人数有所增加；预计这种影响将继续下去。

This grant is supported jointly by the Division of Materials Research and the Chemistry Division. The research is targeted at correlating microscopic structure and macroscopic behavior for fluids and their mixtures, with a particular emphasis on complex fluids. While the research tools are theoretical , the focus is on making connections with experiment and, where appropriate, simulation. An unusual opportunity afforded by this work is the ability to compare the results for the lattice and continuum models using the same theoretical approach. The behavior of complex fluids has been of high interest recently, stimulated by the increasingly sophisticated kinds of measurements accessible to scientists as well as the greatly expanded ability to simulate mixtures of dense fluids. The research proposed here builds upon the work of the PI and her group in using the Born-Green-Yvon (BGY) integral equation technique to model lattice and continuum fluids and mixtures. The lattice theory yields simple closed-form expressions for thermodynamic quantities. Advantages include its accessibility to non-theorists, and the ability to test it using lattice simulation results on complex systems. The continuum theory is capable of tackling more subtle issues involving the interplay between local structure and bulk properties. However, numerical methods are required and simulation data on mixtures are limited. The development of analogous lattice and continuum theories creates opportunities for determining which properties are sensitive to the imposition of a lattice constraint. The lattice studies proposed here focus on three projects: re-deriving the BGY theory to describe films and interfaces and studying the transition to the bulk; increasing the complexity of systems studied to include ternary mixtures; and mapping the thermodynamic results of the BGY theory onto the formalism of the Flory-Huggins chi parameter, the most widely-used characteristic parameter in the polymer community. This work will build on the demonstrated ability of the lattice BGY theory to describe simple and polymeric fluids and mixtures, and will exploit recently developed strategies for extracting much information from a minimal amount of experimental data. On the continuum side, the BGY theory has been used recently to study square-well fluids of up to 16-mers, and n-alkanes. These results will inform the proposed study of small branched alkanes, a project which will lead to a greater understanding of packing effects on fluid properties, and consequently of what may be lost when the lattice BGY theory is used. The second project focuses on square-well mixtures of short chain fluids; the components will range between monomers and 8-mers, thereby stretching the limit of current simulation results. This research will require consideration of the concentration dependence of the inter- and intramolecular distributions: how to treat it, and under what conditions it will become important. In this work connections between experimental data/analysis and the theoretical tools developed by the PI to study complex fluids will be expanded and strengthened. The outcome is that a more sophisticated combination of strategies, accessible to the materials community, will be available in solving problems relating to understanding connections between microscopic structure and macroscopic behavior. Local presentations by undergraduates and graduates will help them develop teaching skills. Results will also be disseminated through conference presentations by the PI and her research group at national meetings, and publications. The PI's efforts in research and teaching mentorship has resulted in an increase in the number of women in the ranks of graduate and postgraduate students and in faculty; it is expected that such effects will continue.