Ultra‐strong velocity dependence of dynamic contact angle for water intrusion at the nanoscale

Abstract Understanding and manipulating water intrusion at the nanoscale have increasingly attracted much interest in nature and technology. A velocity‐dependent dynamic contact angle (DCA), as a boundary condition, serves a vital function in an advancing water front. However, an understanding of DCA mechanisms remains limited. Here, we develop a universal theory for DCA jointly produced by the friction dissipation near the contact line region and the viscous energy losses at the bulk meniscus, molecular movements overcoming these two modes of dissipation are characterized as slip velocity and bulk velocity in hydrodynamics, respectively. We find that contact angle significantly changes with velocity during water intrusion into nano‐capillaries with different wettability, spanning from superhydrophilic to superhydrophobic. Our results demonstrate that the velocity dependence of DCA can be readily strengthened or suppressed by tuning confinement or wettability of nano‐capillaries, which can be further used to manipulate nanoscale water flow at a more precise level.