Comparison of microscopic dynamics and continuum theory for Poiseuille and diffusioosmotic flows in a microchannel

Abstract

Diffusioosmotic flows in a microchannel are investigated using microscopic coarse-grained particle-based simulations that incorporate molecular interactions between fluid particles and channel walls. The fluid–wall molecular interactions, coupled with concentration gradients, generate flows in the potential regions where the interactions are effective, thereby driving global flows in the bulk. Fluid velocities in narrow potential regions obtained from simulations are quantitatively compared with predictions from continuum theory that accounts for density and viscosity variations. While continuum theory adequately predicts enhanced flow velocities throughout the channel, it does not fully capture flow behaviors in regions of very low fluid density near the wall, revealing its limitations. Friction between the fluid and the wall can be controlled by temperature. As temperature decreases, friction is reduced, which makes the wall surface more slippery. In addition, Poiseuille flows driven by gravity are simulated using microscopic dynamics incorporating fluid–wall molecular interactions. Fluid velocity slips near the wall, and corresponding enhancements in flow velocities throughout the channel are quantitatively analyzed by comparing simulation results with theoretical predictions that account for viscosity variations in the potential region.