CAREER: Drop impact dynamics and fingering on thin liquid films

工程师、物理学家和普通公众都被水滴撞击坚硬表面时形成的皇冠的美丽图像所吸引。除了令人着迷的图像外，水滴撞击、扩散、回缩和破裂在农业、喷墨和微电子打印、喷涂、燃烧、能源生成和法医科学中具有广泛的技术意义。尽管有许多用途，但由于(A)表面张力、粘度、惯性和重力之间的复杂相互作用，以及(B)在表面涂覆精确控制亚微米液体层的表面的挑战，对液体薄膜的液滴冲击动力学迄今尚未完全了解。微/纳米加工的最新进展通过操纵流体-结构相互作用实现了这一点。该研究项目的主要目的是提供对液滴冲击薄膜的基本理解。该项目将包括紧密结合的教育和推广计划，包括本科生和研究生水平的多年学生指导，以及通过两个主要公共场所：密歇根大学自然历史博物馆和Xplore工程，激励、启发和丰富K-12学生的教育经验的社区推广。研究计划的目标是利用实验和理论建模来全面了解液层厚度小于1微米的液体薄膜上的液滴撞击动力学。该研究计划使用最先进的微/纳米工程表面涂覆已知厚度的润滑膜，研究液滴撞击动力学，主要有三个目标：1)了解液滴撞击光滑且可变形的液膜时空气的作用，液滴和润滑剂涂层之间的液-液接触；2)确定环形润湿脊对指进和液滴破碎的作用；3)了解随之而来的流体动力不稳定性的根本原因，以及从径向扩展的液膜分叉出的卫星液滴的数量。研究的目的是捕捉液滴和润滑层之间的密度和粘度失配对破碎机理的影响。通过结合高速可视化、荧光显微镜、白光干涉显微镜、反射干涉对比显微镜和平面激光诱导荧光，拟议的研究有望产生新的知识，并指导未来在软物质物理和流体力学方面的研究。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Engineers, physicists, and the general public have been fascinated by the beautiful images of the crown that forms when a drop impacts a rigid surface. Besides the mesmerizing images, drop impact, spreading, retraction, and breakup has broad technological implications in agriculture, inkjet and microelectronics printing, spray coating, combustion, energy generation, and forensic science. Despite the many utilities, drop impact dynamics on thin liquid films is not fully understood to date due to (a) the complex interplay between surface tension, viscosity, inertia, and gravity and (b) the challenge of coating surfaces with precisely controlled sub micrometer liquid layers. Recent advances in micro/nanofabrication have enabled this by manipulating fluid-structure interaction. The principal aim of the research program is to provide fundamental understanding of drop impact on thin liquid films. The project will encompass closely integrated education and outreach programs including multi-year student mentoring at the undergraduate and graduate levels and a community outreach to motivate, inspire, and enrich the educational experience of K-12 students through two major public venues: University of Michigan Museum of Natural History and Xplore Engineering.The goal of the research program is to use experiments and theoretical modeling to develop a comprehensive understanding of drop impact dynamics on thin liquid films where the liquid layer thickness is less than one micron. Using state-of-the-art micro/nanoengineered surfaces coated with a lubricant film of known thickness, the research program investigates drop impact dynamics with three principal objectives: 1) understanding the role of air entrapment when a drop impacts a smooth and deformable liquid film featuring liquid-liquid contact between the drop and the lubricant coating, 2) identifying the role of the annular wetting ridge on fingering and drop breakup, and 3) understanding the root cause of the hydrodynamic instability that ensues impact and the number of satellite drops that bifurcate from the radially expanding liquid lamella. The research aims to capture the effects of density and viscosity mismatch between the drop and the lubricant layer on the breakup mechanism. By combining high-speed visualization, fluorescence microscopy, white light interferometry, reflection interference contrast microscopy, and planar laser-induced fluorescence, the proposed research is expected to produce new knowledge and guide future research in soft matter physics and fluid mechanics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.