Mechanistic analysis of droplets blocked at junctions of serial wedge pattern

Abstract

Serial wedge pattern has garnered significant interest for its potential applications in rapid and long-distance liquid transport. However, the occurrence of droplets being blocked at junctions of the serial wedge pattern poses a critical challenge to droplet transport. In this paper, the blocking of droplets is introduced in detail, and the condition of the blocking is systematically investigated. The threshold of blocking is quantitatively represented by the width difference between the wide and narrow ends of wedge (ld). Pinning resistance encountered by droplets when detaching from junctions is a primary cause of blocking. The pinning resistance leads to the droplet tails being torn off. It has been observed that ld plays a crucial role in ensuring smooth droplet transport on the serial wedge pattern and preventing blocking. Larger volume of droplets negatively influences passage by reducing the transport velocity. Conversely, increasing the volume of droplets helps restrain the torn-off tail. Optimizing the curvature at junctions mitigates blocking by not only increasing transport velocity but also decreasing the volume of the torn-off tail. A systematic understanding of the mechanism of blocking can significantly advance the practicality of pumpless droplet transport on the serial wedge pattern.