In order to reduce the spread of COVID-19, the University of Illinois has enacted several measures, including cancelling or postponing large gatherings. With that in mind, the Department of Chemical and Biomolecular Engineering has suspended its public seminars and lectures until further notice.
Energy losses arise as two contacting surfaces move against each other. The need to engineer friction at the microscale is increasingly important in technologies as diverse as soft robotics, geosciences, and consumer products. In this seminar, I will describe our journey from the classical field of particulate suspensions to the futuristic applications of tactile engineering. The first part of the talk will focus on the role of particle roughness in the rheology, structure, and dynamics of concentrated colloidal suspensions. We find that shear thickening, exemplified by the ability to run on cornstarch pools, is a strong function of the particle morphology. We discuss ways to quantify contact between particles, and how it could be used to understand non-monotic trends in the shear thickening and phase behavior of the suspensions. The second part of the talk will focus on the coupling between solid and fluid in a soft lubricated contact when microtextures are present. We develop a scaling framework using Reynolds' equations and solid deformation to capture the elastohydrodynamic lubrication of patterned tribopairs involving elastomers, thermosets, and hydrogels. Remarkably, the model captures the frictional behavior of entirely different setups: a bench-scale tribo-rheometer, a robotic finger, and real human fingers. Our results demonstrate that the tactile mechanics of soft materials can be engineered using a combination of pattern geometry, material elasticity, and fluid properties. The scaling framework opens up new ways to incorporate materials science into the futuristic engineering of haptic devices.