The Effect of Detaching Force on the Droplet Residue on a Fiber

The adherence to, and removal of droplets from cylindrical fibers underlie applications from fog harvesting, oil–water, and water transport in fuel cells. When the droplets are forcibly removed from hydrophilic fibers, the ease of detachment strongly depends on droplet volume and the rate of the process controlled by the applied force. In the present work, we study the mechanism of water droplet detachment and retention of residual water on smooth hydrophilic fibers using nonequilibrium molecular dynamics simulations. We extract scaling relations that allow extrapolation of our findings to larger length scales that are not directly accessible by molecular models. Our studies of the droplet breakup uncover a strongly nonmonotonic influence of external force, with the amount of residual water maximized under the intermediate force strengths whereas a complete or near-complete detachment of the droplet can be achieved in both extremes, with the applied force only slightly, or considerably exceeding the minimal force of detachment. The strength of this force decreases with the size of the drop, while the maximal residue increases with the droplet volume, V, sub-linearly, in proportion to the V^2/3.