Simulation and experiments on the capillary forces between two continuously fully wet circular disks

The capillary force of the axisymmetric liquid bridge between two continuously fully wet disks is investigated. The energy minimization method shows excellent consistency with the method based on the Young-Laplace equation. The capillary force between two disks is typically repulsive at small distances, and becomes attractive with increasing separation distance for a fixed liquid volume. In addition, the radius ratio of the two disks has a crucial effect on the capillary forces. The mean curvature, pinned contact angles, and rupture distance of the liquid bridge between two disks of various sizes are characterized. The mean curvature of the liquid bridge first decreases; after a minimum value is achieved, it gradually increases. When the two disks are of equal size, the pinned contact angles are identical. When the two disks have unequal radii, the pinning angles of the liquid at the upper and lower disks tend to coincide with the increase in separation distance. The rupture distance decreases with the increase in the ratio of the radii of the bottom disk to the top one. Finally, the force-distance curves for fully wet circular disks have been experimentally verified, and good consistency has been found.