Viscous force during tangential separation of meniscus bridges

Abstract

Viscous force can be significant and become one of the main reliability issues when a tangential sliding operation is needed, as is common for a number of micro/nano devices. In this study, equations for viscous force during tangential separation of two flat surfaces, a sphere and a flat surface, are developed. The effects on viscous force due to separation distance, initial meniscus height, separation time and roughness are presented. Viscous force increases with an increase in separation distance. The force decreases with an increase in initial meniscus height for the separation of two flat surfaces, whereas the opposite occurs in the separation of a sphere and a flat surface. Viscous force is inversely proportional to separation time. The introduction of roughness leads to a rapid decrease in viscous force. The decrease in viscous force is inversely proportional to square root of the number (1/) of asperities. The study provides a fundamental understanding of the physics of the tangential separation process and may be useful for the control of forces in the design of micro/nano devices.