Wicking dynamics into two-rail open channel with periodical branches

Abstract

Wicking into open channels with branches is frequently adopted in multiple assays for medical testing. The penetration velocity plays a key role in improving efficiency. However, it is significantly reduced in the bifurcation microfluidic systems. As a result, understanding and enhancing wicking dynamics in bifurcation capillary flow is imperative. Capillary imbibition into a two-rail channel with periodical branches is investigated by many-body dissipative particle dynamics. The influences of the branch width and surface wettability on the penetration velocity and imbibition flow rate are examined. Four different types of spontaneous capillary flows are observed, including no invasion into branches, reduction in the penetration velocity, stick-slip motion, and inter-branch gap covered by liquid. Four regimes are identified accordingly, the phase diagram relates the flow behavior to the branch width, and surface wettability is established. As the branch width is significantly large (small gap), the penetration velocity is found to be greater than that without branches. It is attributed to the partial covering behavior, which leads to the effective width more than the main channel width.