Thermodynamics and Structure of Chemically Heterogeneous Solid-Liquid Interfaces

University Of Kansas Center For Research Inc, Lawrence KS

Investigators

Abstract

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.