CAREER: Squeezing and Shear Behaviors of Liquid Films in Confined Geometry

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The research objective of this Faculty Early Career Development (CAREER) grant is to develop a computational framework to investigate several fundamental issues in the surface force apparatus (SFA) and atomic force microscope (AFM) experiments. Liquid films confined between two deformable solid surfaces play a central role in friction and lubrication. Driven by the interest in miniaturization of devices to nanometer scales, there is a compelling need to understand how the molecular films react to external loading under squeezing and shear in a confined geometry. This seemingly simple yet ubiquitous question involves not only complicated evolutions of the structure and dynamics of the confined fluids, but also complex relaxations of the confining solids. The liquid-vapor molecular dynamics (LVMD) simulation coupled with a driven dynamics algorithm with stress boundary conditions will focus on three critical issues: (1) the nature of the layering transition of the confined fluids in the SFA experiment, especially the nature of the n - n - 1 layering transition in the Persson and Tosatti's nucleation-growth model proceed, (2) the structural properties and the shear behaviors of liquid films in the SFA experiment, and (3) the squeezing and shear behavior of liquid films in the AFM experiment.If successful, the research effort will lead to many fundamental yet long-standing controversial questions in the surface force science community, such as the squeeze-out mechanism, the structural properties and shear behaviors of liquid films in SFA and AFM experiments, to be answered. Advancements in these computational studies will significantly enhance our understanding of the nanotribological properties of nanoconfined liquid films. The integrated education plan focuses on exposing and training graduate and undergraduate students in simulation-based engineering and science (SBE&S) research by directly engaging them in the development of large-scale computational codes and algorithms. The research effort will enrich the PI's Computational Nanoscience graduate class, and Materials Science and Engineering undergraduate class teachings, and will promote more undergraduate students to be involved in SBE&S research. The education outreach activities will be extended to high school students from The School Without Walls (SWW), a Washington DC public high school to promote SBE&S education through summer internship program. Therefore, this CAREER project will benefit the students, the educator, and society in many aspects.