Design and fabrication of inverted tapered micro-pillars for spontaneously transporting liquid upward

Abstract

Directional liquid transport has significant domestic and industrial applications. Theoretically, tapered objects can transport a liquid droplet horizontally or along a small slant angle: Many biomaterials have already demonstrated this ability. However, spontaneously transporting liquid in the vertical direction has been challenging. In this study, a numerical model was developed to simulate the transporting process and design inverted tapered pillars. The range of acceptable parameters for the pillar’s geometry was obtained. When the taper angle, the diameter of the bottom end of the pillar, and the contact angle of the liquid are less than 10°, 80 μm, and 54.5°, respectively, then liquid may be transported upward spontaneously. An experimental setup for fabricating the pillars was also developed and presented. With this setup, the designed pillars were successfully fabricated by the gradient electrochemical corrosion method and enhanced its wettability by the electrochemical modification method. The fabricated pillars were then experimentally validated, showing that they can spontaneously transport a micrometer-scale droplet upward. These results may provide a new and systematic way to design and fabricate a tool for high-efficiency liquid transport.