Thermoresponsive switching of liquid flow direction on a two-face prism array

We present a simple approach to reversibly switch the direction of liquid flow on physically symmetric and chemically asymmetric prism structures by exploiting the reversibility of surface wetting properties of a thermo-responsive polymer, poly(N-isopropyl-acrylamide). Such an asymmetric prism array creates a flow path in the direction of the lower critical contact angle. This allows a unidirectional "step flow" across the ridges of prism channels, which can be made reversible with a suitable temperature change.