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

这项教师早期职业发展（Career）基金的研究目标是开发一个计算框架来研究表面力仪器（SFA）和原子力显微镜（AFM）实验中的几个基本问题。液体薄膜被限制在两个可变形的固体表面之间，在摩擦和润滑中起着核心作用。在器件小型化到纳米尺度的兴趣驱动下，迫切需要了解分子膜在有限几何形状下在挤压和剪切下对外部负载的反应。这个看似简单却无处不在的问题不仅涉及到受限流体结构和动力学的复杂演化，还涉及到受限固体的复杂松弛。结合应力边界条件下驱动动力学算法的液汽分子动力学（LVMD）模拟将重点关注三个关键问题：(1) SFA实验中受限流体层状转变的性质，特别是Persson和Tosatti的成核-生长模型中n- n- 1层状转变的性质；(2)SFA实验中液膜的结构性质和剪切行为；(3)AFM实验中液膜的挤压和剪切行为。如果取得成功，这项研究工作将导致许多表面力科学界长期存在的基本问题，如挤出机制，SFA和AFM实验中液膜的结构性质和剪切行为，得到解答。这些计算研究的进展将大大提高我们对纳米受限液体膜的纳米摩擦学特性的理解。综合教育计划的重点是通过直接参与大规模计算代码和算法的开发，使研究生和本科生在基于仿真的工程与科学（sbe&s）研究中暴露和培训他们。这项研究工作将丰富PI的计算纳米科学研究生班和材料科学与工程本科班的教学，并将促进更多的本科生参与SBE&amp；S的研究。美国华盛顿特区公立高中“没有围墙的学校”（SWW）的高中学生将参加此次教育推广活动，通过暑期实习项目推广sbe&s教育。因此，这个CAREER项目将在许多方面有益于学生、教育者和社会。

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.