Long range signature of liquid's inertia in nanoscale drainage flows†

In confinement, liquid flows are governed by a complex interplay of molecular, viscous and elastic forces. When a fluid is confined between two approaching surfaces, a transition is generally observed from a long range dynamical response dominated by viscous forces in the fluid to a short range elasto-hydrodynamic response due to the elastic deformation of the solid materials. This study investigates the behavior of fluids driven between oscillating solid surfaces using a dynamic Surface Force Apparatus. Our findings reveal that the dominant influence on fluid behavior arises from long-range inertial effects, superseding conventional elasto-hydrodynamic effects. Through systematic experimentation involving fluids of varied viscosities, diverse substrates, we identify key parameters and develop a comprehensive model which explains our measurements. Our findings not only provide insights into confined fluid dynamics but also offer practical implications for various applications in microfluidics, nanotechnology and liquid lubrication.