Developing a Theory of Relaxation Dynamics for Fluids Confined in Porous Materials

这个奖项是根据2009年美国复苏和再投资法案(公法111-5)资助的。该项目支持开发和应用建模技术的研究计划，该技术可以同时描述受限于多孔材料中的流体的热力学和动态传输现象。这项工作的科学动机有两个方面。一个动机是需要了解介孔材料中的吸附脱附滞后现象。在这些系统中缺乏真正的均衡，这使得理解动力学变得特别有趣。另一个动机是对吸附等温线中平衡的传输阻力以及这些阻力如何依赖于多孔材料的结构有更深入的了解。这些都是由来已久的问题，甚至在某种意义上都是经典的。然而，该项目建议进行建模研究，以开发对热力学和传输现象的一致描述。这有可能在这一领域做出真正的变革性贡献。我们在这里采取的方法是发展一个关于体系中含时分子密度分布的理论。然后，我们根据系统状态之间的跃迁概率来考虑这种分布的动态演化。我们使用格子气体模型来描述系统中的相互作用，而PI理论，动态平均场理论(DMFT)，给出了系统平衡态和亚稳态的平均场(经典密度泛函)描述。这项研究包括以下几个部分：i)DMFT在各种模型孔几何结构中的应用。他们将选择说明孔隙结构对松弛动力学的影响的几何图形。Ii)应用于实际系统中的孔道几何。他们将研究独立的孔系统，包括MCM 41和多孔硅，有序孔网络系统，如Kit 6和SBA 16，以及以多孔玻璃为例的无序孔网络系统。Iii)发展一种输运和自扩散理论。DMFT也可以从扩散的角度进行分析，并提供了输运扩散系数和自扩散系数的理论。四)汞孔隙度测定仪的应用。我们将使用DMFT来了解汞渗透法中汞捕获的性质，这是在他们最近的工作基础上进行的，该工作展示了如何在单个框架中对气体吸附和汞渗透法进行建模。五)准确性评估和进一步发展。他们将使用川崎动力学和分子动力学模拟对该方法中内置的近似的影响进行详细评估。他们还研究了理论中的热涨落，并计划将该方法扩展到非晶格分子模型。本文提出的研究在本质上是基础性的，并解决了受限于多孔材料中的流体的动态松弛的纳米尺度模拟。这是一项潜在的变革性研究，因为它将在受限流体性质领域的两个研究界之间架起一座桥梁：一个主要侧重于吸附测量和热力学，另一个侧重于运输现象。直接的影响是多孔性材料表征方法的发展。然而，鉴于全世界在开发从分离、催化到微电子等各种应用的新型多孔材料方面所做的非常广泛的努力，最终的影响可能是非常广泛的，包括与能源有关的应用。该项目有许多教育组成部分，包括本科生的研究经验，与社区大学的接触，以及根据研究为热力学、反应工程和运输现象的本科课程开发课程材料。

0853068Monson"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Intellectual Merit. This project supports for a research program on development and application of modeling techniques that can simultaneously describe both thermodynamic and dynamic transport phenomena for fluids confined in porous materials. The scientific motivation for this work is two fold. One motivation is the need to understand adsorption desorption hysteresis in mesoporous materials. The absence of true equilibrium in these systems makes it of particular interest to understand the dynamics. Another motivation is to develop a more sophisticated understanding of the transport resistances to equilibration in adsorption isotherms and how these depend on the structure of the porous materials. These are both problems with long histories and are even in some sense classical. However, the project proposes modeling research on developing a consistent description of both the thermodynamics and transport phenomena. This has the potential for a truly transformative contribution in this field. The approach we take here is to develop a theory of the time dependent molecular density distribution in the system. We then consider the dynamic evolution of this distribution in terms of the probabilities of transitions between states of the system. We use a lattice gas model to describe the interactions in the system and the PIs theory, dynamic mean field theory (DMFT), yields a mean field (classical density functional) description of the equilibrium and metastable states of the system. Ther proposed research has following components: i) Application of the DMFT to a variety of model pore geometries. They will choose geometries that illustrate the impact of pore structure on the relaxation dynamics. ii) Application to pore geometries in real systems. They will study systems of independent pores, including MCM 41 and porous silicon and ordered pore network systems such as KIT 6 and SBA 16, as well as disordered pore network systems exemplified by porous glasses. iii) Developing a theory of transport and self-diffusivities. The DMFT can also be analyzed from the point point of view of diffusion and provides a theory of transport diffusivity as well as self diffusivity. iv) Application to mercury porosimetry. We will use the DMFT to understanding the nature of mercury entrapment in mercury porosimetry, building on their recent work showing how gas adsorption and mercury porosimetry can be modeled in a single framework. v) Accuracy assessment and additional developments. They will make a detailed assessment of the impact of the approximations built into the approach using Kawasaki dynamics and molecular dynamics simulations. They also investigate including thermal fluctuations in the theory and plan to investigate an extension of the approach to off lattice molecular models.Broader Impacts. The research proposed here is fundamental in nature and addresses the nanoscale modeling of dynamic relaxation for fluids confined in porous materials. This is potentially transformative research since it will provide a bridge between two research communities in the area of confined fluid properties: one that focuses primarily on adsorption measurements and thermodynamics and the other that focuses on transport phenomena. The immediate impact is in the development of characterization methods for porous materials. However, given the very extensive world-wide effort in developing new porous materials for applications ranging from separationsto catalysis to microelectronics the ultimate impact could be very broad including energy-related applications. The project has a number of educational components including research experience for under- graduates, outreach to community colleges and development of course materials for undergraduate courses in thermodynamics, reaction engineering and transport phenomena based on the research.