Analytical, numerical and experimental study on capillary flow in a microchannel traversing a backward facing step

Furthermore, an analytically derived geometric condition required for spontaneous capillary flow over a BFS was developed. To validate the flow condition, experimental measurements were performed on microchannels with BFSs fabricated in silicon using deep reactive ion etching with aspect ratios ranging from 1.5 to 3.8. The contact angle of surfactant/water solutions ranged from 50° to 85° on the silane-treated silicon surfaces and from 93° to 100° on the PDMS top surface for the closed structure experiments. The experimental results were in good agreement with the analytically derived condition. The developed model is an enabling tool for designers of capillary-driven microfluidic systems.