Rate Effects on Dynamic Properties of Liquid under Nanoconfinement

Abstract

The dynamic properties of liquids in confined geometries or porous media are of both fundamental and practical importance in many physical situations, such as lubrication of micro/nanoelectromechanical systems, the flow of liquids in rocks and nanopores, and transport through porous media in filtration processes. The investigation of liquids confined at the nanoscale has been an active field for many years, but their properties remain controversial. In this work, a surface force apparatus (SFA) has been used to investigate the dynamic properties of nanoconfined octamethylcyclotetrasiloxane (OMCTS) between two mica surfaces. The dependences of normal and adhesion forces on different confinement or retraction rates were studied. The hydrodynamic effects and liquid drainage were also determined. The contribution of hydrodynamic effects to liquid drainage is limited. Our experimental results showed that normal forces are strongly changed at high loading rates, whereas adhesion forces vary slightly. The rapidly confined film behaves as a jamming liquid of enhanced viscosity for a film thickness below to a few nanometers, while the viscosity change little at slow confinement rate. These results indicate that confining rate effects play a great role in the properties of nanoconfined liquid.