Sunlight-Driven Water Transport via a Reconfigurable Pump.

Fast and controllable water transport in microchannels has implications for many applications. A combination of stimuli-responsive asymmetrical changes in the geometry and gradient in the surface wettability offers the possibility to accelerate the transport and realize controllability. Herein, we introduce a meters-long sunlight-powered reconfigurable water pump constructed by tubular poly(dimethylsiloxane) (PDMS) premixed with chemically reduced graphene oxide (rGO), in which the inner wall is modified with thermal-sensitive poly(N-isopropylacrylamide) hydrogel (PNIPAm). This sunlight-powered water pump delivers a record-high advance speed of 1.5 mm s-1 and 13.6 kg h-1  m-2 under 1.5 sun. Theoretical and experimental results reveal that the remarkable performance results from the synergistic effect of the contact-angle gradient arising from the reversible hydrophilic/hydrophobic switch of PNIPAm and the capillary force arising from the geometric deformation of the microchannel.