Self-driven penetration of droplets into non-wetting capillaries

Abstract

This is a successive study to our previous study published in this journal. In the present study, a further numerical study on the penetration of a droplet into non-wetting capillaries is carried out by using many-body dissipative particle dynamics (MDPD). The simulation results show the outer (outside of the capillary) and inner (inside of the capillary) curvatures of the droplet can cause two Laplace pressures. The difference between these two pressures forms a net pushing force which directly drives the droplet flowing into the non-wetting capillary. We give a detailed analysis on how the outer and inner curvatures change during the penetration process. To further show the effect of the Laplace pressure difference on the droplet movement, we also simulate a new droplet/capillary/film system. In this system, the droplet and liquid film are placed at both ends of a prefilled capillary. It is very interesting to find that the droplet penetrates even faster in lyophobic capillaries over lyophilic ones, and the spontaneous penetration does not pose any wettability restriction which is different from previous study in literatures. The present work is expected to provide new ideas for designing microfluidics or nanofluidics devices by utilizing the driving force from the droplet itself.