Liquid-Diode Microtubes Sculpted by Dissolution

Directional transport of liquids is of great importance in microfluidics, biomedical engineering, and energy saving. Despite considerable progress in engineering various open surfaces to achieve liquid manipulation, the realization of diode-like liquid transport in enclosed spaces is still challenging. Here, a liquid-diode microtube is presented for directional liquid transport within confined spaces by controlling dissolution. The microtubes exhibit gradient ratchet structures on the inner wall, sculpted by the interfacial instability during the dissolution process. Under the effect of asymmetric pinning and Laplace pressure, such microtubes selectively enable directional liquid transport in closed channels. More importantly, liquid diodes are fabricated as assembly units with opposite diode-enforced directions for the industrial oil-water separation. These results demonstrate the capacity of liquid-diode microtubes sculpted by dissolution for directional and passive liquid transport, potentially paving the way for oil-water separation in industrial applications.