Normal force induced by viscoelastic flow between confined surfaces

Particle dynamics and lubrication flows for a particle moving near a confining boundary in viscoelastic surrounding are widely encountered and of essential significance in biophysics, nature and engineering application. Different from normal force of confined particle in viscous fluid caused by geometry and inertial effect in high Reynolds number, viscoelastic fluid under shear shows normal stress. In this talk, we aim to clarify the elasticity-induced normal force and justify the contributions from elastic effect and soft boundary. Our study focuses on flow in small Re while Wi number is in a wide range from 0.05 to 10. Large elastic effect will be introduced for large elasticity number El = Wi / Re >> 1. We deduce a theoretical expression of elasticity-induced normal force based on scaling analysis and numerical simulation, which unveils major factors dominating normal force and characteristic length scale. The analysis is further applied to the situations with the presence of a soft boundary, and we show normal force in viscoelastic fluid can be in magnitude dominant to that of elastohydrodynamic one in micro- and nanofluidic. Overall, our findings could provide helpful insights to understand nonintuitive migration behaviors of particles in various biophysical applications.