Directional step flow across ridges on multiscale two-face prism array

Directional wetting or spreading on asymmetric structures have received much attention because of their potential to control the liquid flow in microfluidic devices. Although there have been many reports on directional liquid flows, the flow speeds of the directional flows could not be predicted. Here, we present a controllable strategy for directional flow on a multiscale two-face prism array, one face is smooth and the other face is roughened. The polymeric surface of the prism is roughened by oxygen plasma while the other side is blocked by a coated metal film. With the designed structure, we demonstrate a unidirectional liquid flow and manipulate the flow speed in an open channel. From a simplified model suggested here, the flow speed could be predicted quantitatively.

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