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

相互接触的两个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应用中非常重要。通常，当两个表面以增加的力压在一起时，使两个表面滑动分开所需的横向力增加。最近的工作发现了这不是真的情况下，即，当两个表面以增大的力压在一起时，将表面滑动分开变得更容易。在某些液体与选定的固体表面接触滑动的情况下，已经观察到这种意想不到的行为。由于固体上的液体润滑是许多系统的关键部件（即，润滑汽车发动机的油），了解这种效应可能在技术上和社会上都有很大的好处。该项目的目标是更好地了解表面上液滴的行为，并开发一种更好的方法来预测液体-固体表面运动时所施加的力。提出了一个新的描述界面相互作用的性质，即界面模量。这项工作将被用来作为一系列教育推广活动的基础，以高中学生，并为本科生提供研究经验，包括对学生的代表性不足的群体的重点。摩擦学科学教导，横向摩擦力随着两个表面之间的接触面积增加而增加，并且摩擦力与法向力成比例。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加，但是横向力随着法向力减小。这一发现是由一种新的仪器，离心粘附天平（CAB），允许独立控制和测量两个接触表面的法向和侧向力。 将进行系统的研究，从而建立一套模型流体/固体系统的表面化学和物理性质之间的关系，界面模量和表面损伤。表面粗糙度预计将是一个关键参数和一系列的纳米结构表面包括在研究中。

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.