Control of Droplet Movement on an Inclined Wall by Difference of Wettability

Abstract

Recently it is strongly demanded to manipulate a liquid droplet in lab-on-chip or micro reactors used in chemical engineering devices. This study concerns the control of the movement of liquid droplet on an inclined plate, using the difference of wettability caused by the chemical structure change of a polymer which is resulted from the irradiation of ultraviolet rays. The behavior of droplets was carefully observed experimentally when it enters into the irradiated area having an oblique boundary to the moving direction. Considering the surface tension acting on the perimeter with different contact angles, the movement of droplet was analyzed theoretically. The calculated results approximate well the actual behavior of droplet. Then we proposed a geometric pattern of irradiated area in which the droplet could be moved linearly with a constant angle to the gravitational direction. The experimental observation shows that the droplet behavior was successfully controlled to be moved along on the line of geometric pattern.