Directional Droplet Spreading Transport Controlled on Tilt‐Angle Pillar Arrays

Abstract

Abstract The controllable unidirectional spreading of droplet on tilt‐angle pillar arrays (TPAs) composed of epoxy resin (TDE‐85) and polyethylene glycol is presented. TPAs are fabricated via soft lithography with multimolding steps that coupled with a directional heat‐pressing and temperature controlling process, in which tilt‐angle structures are generated by using temperature‐responsive shape memory polymers and then act as mold. TPAs with different tilt angles (e.g., unidirection and opposite directions) are thereby obtained. It is found that the TPAs propel the droplet directional spreading or droplet contrasting spreading effectively. On the wettability‐optimized TPAs, the droplet can achieve the strong anisotropy with high length/width ratios (i.e., 11/1). Furthermore, unique TPAs with contrasting tilt angles can achieve the two droplets to form the contrasting spreading so as to gather together as a microreactor. It is revealed that such controlled spreading ability of TPAs is attributed to the cooperation of gradient surface energy resulted from the effect of tilt angles and the controllable surface wettability. The findings offer insights into the design of novel fluid‐controlling surfaces, which can be extended to some realms, e.g., microfluidics or microreactors.