Thermodynamics and Structure of Chemically Heterogeneous Solid-Liquid Interfaces

堪萨斯大学的Brian B. Laird因其对固液界面的理论和计算研究而获得化学学部化学理论、模型和计算方法项目的奖项。这种界面在自然界和技术中都很常见，从通常观察到的冰和水之间的界面到溶液中的纳米颗粒表面。了解这种界面的结构和热力学在包括化学、材料科学、纳米工程、冶金、胶体科学和生物物理学在内的广泛领域都很重要。例如，形成特定固液界面的能量成本控制着液体是完全覆盖（或湿润）固体表面，还是像刚打过蜡的汽车上的水一样凝结成水滴。然而，对固液界面的直接实验研究是困难的，特别是对于金属系统，高温和光谱探针缺乏透明度严重限制了实验研究。因此，计算方法对于开发界面区域的详细原子级图像至关重要。在这项工作中，分子模拟技术用于在原子水平上检查所谓的化学非均相固液界面的性质；即，固、液相在化学成分上有显著差异的界面。本研究中使用的特定系统专门用于解决界面科学中的基本问题，同时与特定的技术应用相关，例如了解纳米颗粒在溶液中的稳定性，金属脆化机制和蓝宝石纳米线的生长。该项目还有助于培养学生和博士后在计算化学、液态物理和材料科学方面的技术，并为他们提供先进科学规划方面的丰富经验。这些技能在化学、工程、材料科学、制药科学、生物学和物理学的广泛应用中有着广泛的应用，并且在计算科学和技术的任何方面都具有相当大的市场价值。本研究的总体目标是在基本的分子水平上理解化学非均相固液界面的热力学和结构性质是如何由原子和分子相互作用以及界面几何形状形成的。这一努力需要(a)开发、评估和应用新的计算方法和力场来研究凝聚相之间的界面，以及(b)将现有方法扩展到超出开发方法的系统类别。在这个项目中，一个协调的方案，方法开发，分子动力学模拟和应用统计力学进行系统的研究，化学非均相固液界面的热力学和结构。该项目特别侧重于三类系统：(a)化学非均相金属/金属固液界面，特别是对铝和液态镓之间界面的研究，这是研究液态金属脆化的一个有趣的模型系统。(b)使用氧化铝/铝(l)界面作为试验台的金属/金属-氧化物固液界面——该系统提供了一个难得的机会，可以直接比较原子水平固液界面的实验和模拟结果。(c)曲面流体。研究了波纹表面、凸胶体颗粒和凸表面上的流体系统的界面自由能与曲率的关系。对结果进行了检验，以评估形态计量热力学的有效性，形态计量热力学是最近发展起来的曲面热力学理论。

Brian B. Laird of the University of Kansas is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry Division for the theoretical and computational study of solid-liquid interface. Such interfaces are common in nature and technology, from the commonly observed interface between ice and water to the surfaces of nanoparticles in solution. Understanding the structure and thermodynamics of such interfaces is important in a broad array of fields including chemistry, materials science, nano-engineering, metallurgy, colloidal science and biophysics. For example, the energy cost in forming a particular solid-liquid interface control whether the liquid completely covers (or wets) the solid surface or instead, beads up into droplets, like water on a freshly waxed car. Direct experimental study of solid-liquid interfaces, however, is difficult - especially for metallic systems where high temperatures and lack of transparency to spectroscopic probes severely limit experimental study. As a result, computational methods have been crucial in developing a detailed atomic-level picture of the interfacial region. In this work, molecular simulation techniques are used to examine, at an atomic level, the properties of so-called chemically heterogeneous solid-liquid interfaces; namely, interfaces in which the solid and liquid phases are significantly different in chemical composition. The particular systems used in this study were chosen specifically to address fundamental questions in interface science, while at the same time be relevant to specific technological applications, such as understanding the stability of nanoparticles in solution, mechanisms for metal embrittlement and the growth of sapphire nanowires. The project also contributes to the training of students and postdocs in the techniques of computational chemistry, liquid-state physics and materials science and affords them a considerable experience in advanced scientific programming. These skills have wide use in a vast array of applications in chemistry, engineering, materials science, pharmaceutical science, biology and physics and gives them considerable marketability in any aspect of computational science and technology. The overall goal of this proposed research is to understand, on a fundamental molecular level, how the thermodynamic and structural properties of chemically heterogeneous solid-liquid interfaces are shaped by atomic and molecular interactions and interfacial geometry. This effort requires both (a) the development, evaluation and application of new computational methods and force fields to study the interfaces between condensed phases and (b) the extension of existing methods to classes of systems beyond those for which the methods were developed. In this project, a concerted program of method development, molecular-dynamics simulations and applied statistical mechanics is developed to perform a systematic study of the thermodynamics and structure of chemically heterogeneous solid-liquid interfaces. The project focuses specifically on three classes of systems: (a) Chemically heterogeneous metal/metal solid-liquid interfaces, in particular a study of the interface between aluminum and liquid gallium, which is of interest as a model system for the study of liquid-metal embrittlement. (b) Metal/metal-oxide solid-liquid interfaces using the alumina(s)/Al(l) interface as a test-bed - a system which provides a rare opportunity to directly compare experiment and simulation results for a solid-liquid interface at the atomic level. (c) Fluids at curved surfaces. The curvature dependence of the interfacial free energy for a number of systems is investigated including fluids at corrugated surfaces, convex colloidal particles and convex surfaces. Results are examined to assess the validity of Morphometric Thermodynamics, a recently developed theory of curved surface thermodynamics.