Modeling Nanoscale Confinement of Fluids: Applications to Fluids in Porous Materials and Liquids Wetting Nano-structured Surfaces

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

Monson / 0649552 Intellectual merit: This project is directed at the molecular thermodynamic modeling of fluid properties under nano-scale confinement. In this context, confinement refers on the one hand to the case of fluids in complex porous materials and on the other to when a liquid is in contact with a small scale patterning on a solid surface, where confinement is created by the length scale of the surface patterning. For fluids in porous materials, understanding of fundamental thermodynamic behavior has significant impact on applications ranging from catalysis to adsorption separations to membranes, as well as in the use of adsorption for porous materials characterization. The interfacial wetting of porous, structured or patterned surfaces by liquids has been of considerable interest in many technologies, ranging from the development water resistant textiles to the design of gas-liquid-solid catalytic reactors. Recently, interest is also emerging in applications in nanotechnology where liquids contact solids such as micro- and nano-fluidics, nano-lithography or "lab on a chip" technologies. The research focuses on two areas: (i) Development and application of coarse-grained models for fluids confined in complex pore structures. The investigators are developing a unified modeling approach to fluids in complex pore structures that can treat both wetting fluids (gas adsorption) and non-wetting liquids (mercury porosimetry) in single framework. The research program seeks to understand the equilibrium states of these systems as well as hysteresis and the accompanying dynamics. (ii) Understanding how liquids wet topologically and chemically patterned surfaces. The investigators use density functional theory and molecular simulations to calculate the density distributions for liquid droplets on patterned surfaces. The goal is to understand the fine details of the three-phase solid-liquid-vapor contacting and how this is influenced by the structure of the solid surface. These research areas are linked fundamentally by a common theme of fluid confinement and interfacial wetting phenomena. A central issue for statistical mechanics research in these areas is the need to deal with the three-dimensionality of the density distribution in these systems created by the complexity in the geometry. These models should allow one to bridge the nanoscopic and mesoscopic length scales. This research features several computational methods including mean field density functional theory and Monte Carlo simulation. Broader Impacts: The project represents an example of fundamental research in molecular thermodynamics that is closely linked with important engineering applications. The primary impact of the research is in application to porous material characterization using gas adsorption and mercury porosimetry. The research is creating a single molecular modeling framework for understanding both of these important characterization techniques. Recent research in nanotechnology has shown the importance of understanding interfaces at small length scales. The modeling techniques developed here for studying confined fluids, which focus on three-dimensional interfacial structure, can make a significant impact in this area also. The project has significant educational components, in the first instance through the involvement of graduate students, postdoctoral scholars and undergraduates. Research group activities are designed to develop the ability of students to communicate their research achievements, and our graduate students participate in teaching undergraduate courses as an educational requirement of their degree program. Material developed under NSF support will be used to develop lectures in adsorption thermodynamics for undergraduates and project materials for a course in statistical thermodynamics for chemical engineering graduate students. The project features collaboration with researchers in industry (Quantachrome Corporation) as well as international collaboration with research groups at the University of Leipzig and the Technical University of Berlin.