Critical Behavior In Nanoscale Confined Fluid Systems

利用有限尺寸尺度理论结合计算机模拟方法，研究了纳米尺度孔隙结构模型中受限流体临界行为的基本方面。描述了分析这两类系统中关键现象的原始结果。所开发的框架结合了临界尺度概念，并严格考虑了在临界区域进行模拟时重要的有限尺寸效应。支撑对密闭系统的分析的是气液系统和伊辛系统之间的普遍性假设，这一观点与现代临界现象理论的结果保持一致。所提出的有限尺寸尺度分析导致了非常特殊的条件，这些条件定义了临界行为的开始，从而定义了受限系统中的相变制度。通过这种方式，尺寸依赖性成为模拟的一个盟友，并有助于产生预测这些系统的关键性质和其他感兴趣的基本行为的新方法。了解多孔介质中近临界流体的热力学和输运行为对化学和材料工程的几个研究领域都很重要。其中包括开发利用多孔材料在低体积临界温度下有效储存气体的方法，使用超临界流体化学气相沉积（SFCVD）在多孔介质中沉积金属薄膜，以及使用超临界流体干燥多孔硅和气凝胶。在后一种应用中，干燥过程的轨迹被明确地选择为避免穿越孔内流体的相边界。

ABSTRACT CTS-9706805 Univ. of Rochester Fundamental aspects of the critical behavior of a confined fluid in a model nanoscale pore structure are being investigated utilizing finite-size scaling theory in conjunction with computer simulation methodology. Original results are described for analyzing critical phenomena in there types of systems. The framework developed incorporates critical scaling concepts and rigorously accounts for finite-size effects that are important when doing simulations in the critical region. Underpinning the analysis in the confined system has been the assumption of universality between the gas-liquid and Ising-type systems, a perspective in keeping with the results of modern critical phenomena theory. The finite-size scaling analysis presented leads to very specific conditions that define the onset of critical behavior, and hence the phase transition regime, in the confined system. In this way, size dependence is made an ally of the simulations and helps lead to novel methods for predicting critical properties and other fundamental behavior of interest in these systems. Understanding the thermodynamic and transport behavior of near-critical fluids confined in porous substrates is important to several areas of research in chemical and materials engineering. These include the development of methods for using porous materials to efficiently store gases with low bulk critical temperatures, metallic thin film deposition in porous media using supercritical fluid chemical vapor deposition (SFCVD) and the use of supercritical fluids for drying porous silicon and aerogels. In this latter application, the drying trajectory of the process is chosen to expressly avoid traversing the intrapore fluid's phase boundary.