Counterintuitive wetting route of droplet on patterned hydrophilic surface

Abstract

The wetting transition of a droplet on a patterned hydrophilic surface can occur spontaneously and may further lead to superwetting that has the potential to develop novel technologies in the field of anti-fogging, printing and heat transfer. However, it is still unknown how the wetting transition occurs on such a patterned surface. In contrast to the conventional view that wetting occurs immediately in the vertical direction upon the contact of the droplet with the solid surface due to the capillary force, we find that the droplet spreads first in the horizontal direction if the patterned surface has a large enough roughness. Then, the wetting transition occurs at the periphery rather than in the middle part of droplet, which is termed as "one-dimensional wetting". We ascribe such an interesting phenomenon to the competition between the horizontal force arising from the non-equilibrium surface tension and the vertical capillary force as well as to the different pressure under the droplet, which lead to three different wetting routes. Thus, we hope that this new point of view can be helpful to the understanding of the wetting transition of the droplet on the patterned hydrophilic surface.