Non-slip Vs Slip: The Hydrodynamic Boundary Condition and the Moving Contact Line

Ping Sheng
Hong Kong University of Science & Technology, Hong Kong

Immiscible two-phase flow in the vicinity of the contact line (CL), where the fluid-fluid interface intersects the solid wall, is a classical problem that falls beyond the framework of conventional hydrodynamics. In particular, molecular dynamics (MD) studies have shown clear violation of the no-slip boundary condition. Numerous ad hoc models were proposed to resolve this incompatibility, but none can give realistic predictions in agreement with MD simulations. Consequently, a breakdown in the hydrodynamic description for the molecular-scale CL region has been suggested. We have uncovered the boundary condition governing the moving contact line, denoted the generalized Navier boundary condition (GNBC), and used this discovery to formulate a continuum hydrodynamics whose predictions are in remarkable quantitative agreement with the MD simulation results at the molecular level.

* Molecular Scale Contact Line Hydrodynamics of Immiscible Flows, T. Qian, X. P. Wang and Ping Sheng, Phys. Rev. E68, 016306 (2003).