Understanding the Interaction of Moving Liquid Drops on Solid Surfaces and the Role of a Surface Modulus in Solid-Liquid Systems

两个相互接触的移动表面之间的摩擦、润滑和磨损在从汽车发动机到不粘涂层的各种应用中都是重要的。通常，当两个表面被压在一起时，随着力的增加，滑动两个表面所需的侧向力也会增加。最近的工作发现了不是这样的情况，即当两个表面被压在一起时，随着力的增加，滑动表面变得更容易。在某些液体与选定固体表面接触的情况下，观察到了这种意外的行为。由于固体上的液体润滑是许多系统(例如，汽车发动机的机油润滑)的关键组件，了解这种影响可能会在技术上和社会上带来巨大的好处。这个项目的目标是更好地了解液滴在表面上的行为，并开发一种更好的方法来预测液固表面在运动时所受的力。提出了一种描述相互作用的新性质，即界面模数。这项工作将作为针对高中生的若干教育推广活动的基础，并为本科生提供研究经验，包括侧重于代表性不足群体的学生。摩擦学告诉我们，侧向摩擦力随着两面接触面积的增加而增加，摩擦力与法向力成正比。然而，该研究小组最近的工作发现了一个违反这一基本原则的系统。已经证明，对于固体表面上的某些液体，尽管两个表面之间的接触面积增大，但侧向力随法向力的减小而减小。这一发现得益于一种名为离心式附着天平(CAB)的新仪器，它允许独立控制和测量接触的两个表面的法向力和侧向力。将对一组模型流体/固体体系进行系统的研究，从而建立表面化学和物理性质与界面模数和表面损伤之间的关系。表面粗糙度预计将是一个关键参数，这项研究包括了一系列纳米结构表面。

Friction, lubrication, and wear between two moving surfaces in contact with one another are important in applications ranging from car engines to non-stick coatings. Typically, when two surfaces are pressed together with increasing force, the lateral force required to slide the two surfaces apart increases. Recent work has discovered cases where this is not true, i.e., as the two surfaces are pressed together with increasing force it becomes easier to slide the surfaces apart. This unexpected behavior has been observed in the case for some liquids sliding in contact with select solid surfaces. Since liquid lubrication on solids is a critical component of many systems (i.e., oil lubricating a car engine), understanding this effect could be of great benefit technologically and to society. The goal of this project is to better understand the behavior of liquid drops on surfaces and to develop a better method for predicting the forces exerted on a liquid-solid surface when it is in motion. A new property for describing the interaction of has been proposed, namely interfacial modulus. The work will be used as the basis for a number of educational outreach activities to high school students and to provide research experiences for undergraduate students including a focus on students from under-represented groups. Tribological science teaches that lateral frictional force increases as the contact area between two surfaces increases and that frictional force is proportional to normal force. However, recent work by this research group has uncovered a system that violates this basic principle. It has been demonstrated that for some liquids on a solid surface, lateral force decreases with normal force despite the fact that the contact area between the two surfaces increased. The discovery was enabled by a new instrument, the Centrifugal Adhesion Balance (CAB), that allows for independent control and measurement of the normal and lateral forces for two surfaces in contact. A systematic study will be conducted whereby the relationships between surface chemical and physical properties to the interfacial modulus and to surface damage will be established for a set of model fluid/solid systems. Surface roughness is expected to be a critical parameter and a range of nanostructured surfaces are included in the study.