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

该学院早期职业发展（CAREER）资助的研究目标是开发一个计算框架，以研究表面力装置（SFA）和原子力显微镜（AFM）实验中的几个基本问题。在两个可变形固体表面之间的液膜在摩擦和润滑中起着核心作用。由于人们对将器件小型化到纳米尺度的兴趣，迫切需要了解分子膜在受限几何形状中在挤压和剪切下如何对外部载荷作出反应。这个看似简单却又普遍存在的问题，不仅涉及到封闭流体的结构和动力学的复杂演化，而且还涉及到封闭固体的复杂弛豫。液-气分子动力学（LVMD）模拟与具有应力边界条件的驱动动力学算法相结合，将重点关注三个关键问题：（1）讨论了SFA实验中封闭流体分层过渡的性质，特别是讨论了Bubson和Tosatti成核-生长模型中n-n- 1分层过渡的性质，（2）SFA实验中液膜的结构特性和剪切行为，（3）AFM实验中液膜的压缩和剪切行为。如果研究成功，将引发表面力科学界许多基本但长期存在争议的问题，如挤出机制、SFA和AFM实验中液膜的结构特性和剪切行为等。在这些计算研究的进展将显着提高我们的理解nanoconfined液膜的nanotribological性能。综合教育计划的重点是暴露和培训研究生和本科生在基于仿真的工程和科学（SBE S）的研究，直接让他们在大规模计算代码和算法的开发。这项研究工作将丰富PI的计算纳米科学研究生班，材料科学与工程本科班教学，并将促进更多的本科生参与SBE S研究。教育外展活动将扩大到高中学生从学校没有围墙（SWW），华盛顿特区公立高中，以促进SBE S教育通过暑期实习计划。因此，这个职业生涯项目将有利于学生，教育工作者和社会在许多方面。

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.