CAREER: Discovering the Mechanisms of Liquid Phase Epitaxy and Bringing Intermolecular Forces to the Physics Curriculum

University Of Arizona, Tucson AZ

Investigators

Abstract

Recent breakthroughs in mesoscopic materials have reinvigorated the science of solid-liquid interfaces and shifted its emphasis from bulk thermodynamic descriptions to intermolecular forces. The goals of this project are to establish a central facility for the measurement and mapping of intermolecular and surface forces by atomic force microscopy (AFM) and, through student research, to discover the role of solid surfaces in directing interfacial order formation in an adjoining liquid phase (liquid phase epitaxy). First, the nucleation and overgrowth of a solid phase over a different substrate will be investigated by in-situ imaging in metastable solutions. Studies will focus on differences in growth morphology (wetting vs. island nucleation vs. needle growth) as a function of compatibility between substrate and overlayer. Second, force measurements and soft contact imaging will explore the interfacial self-assembly of surfactant solutions and the templating of lyotropic phases by interfacial micelles. Observed interfacial morphologies will be correlated with theoretical calculations based on optimizing the net interaction energy of the micelle lattice and substrate. The role of temperature in structural phase transitions will be explored using an existing temperature-control cell that operates over the aqueous range of temperatures. The students participating in this research will be trained in a contemporary area of condensed matter physics and will thereby be prepared to enter the scientific/technical workforce. %%% The partial ordering of a liquid film in contact with a solid surface is central to interfacial processes ranging from crystal growth to mesoscopic materials synthesis to boundary layer lubrication. The goals of this project are to uncover the mechanisms of interfacial order formation by the measurement and mapping of intermolecular forces by atomic force microscopy (AFM). This technique uses a sub-microscopic tip or stylus to measure intermolecular forces and to image surfaces at atomic scales by mapping force variations across the surface. Student experimentalists will use force measurements and imaging in liquid environments to investigate the role of solid surfaces in nucleating solid and liquid crystalline phases from solutions. Crystal growth of one mineral on a second, closely matched solid will be imaged in real time and at molecular resolution in supersaturated solutions. Studies will focus on differences in growth morphology versus the degree of mismatch between the atomic structure of substrate and overlayer. The nucleation of liquid crystalline phases of surfactants or detergents by solid surfaces will also be investigated. The observed structures of interfacial layers will be correlated with theoretical calculations, based on optimizing the net interaction energy of the surface and surfactant aggregate layer. The effects of temperature on these phases will be investigated using a special sample cell currently under operation. These results are expected to shed new light on interfacial processes such as detergency and the synthesis of advanced materials by self-assembly. This research will be conducted with students who will be prepared for scientific/technical employment in academia, industry, and government.