The directed, long-range and self-propelled transport of droplets on solid surfaces is crucial for many applications from water harvesting to bio-analysis1,2,3,4,5,6,7,8,9. Typically, preferential transport is achieved by topographic or chemical modulation of surface wetting gradients that break the asymmetric contact line and overcome the resistance force to move droplets along a particular direction10,11,12,13,14,15,16. Nonetheless, despite extensive progress, directional droplet transport is limited to low transport velocity or short transport distance. Here we report the high-velocity and ultralong transport of droplets elicited by surface charge density gradients printed on diverse substrates. We leverage the facile water droplet printing on superamphiphobic surfaces to create rewritable surface charge density gradients that stimulate droplet propulsion under ambient conditions17 and without the need for additional energy input. Our strategy provides a platform for programming the transport of droplets on flat, flexible and vertical surfaces that may be valuable for applications requiring a controlled movement of droplets17,18,19.
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The data that support the findings of this study are available from the corresponding authors on reasonable request.
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This work was supported by the National Natural Science Foundation of China (21603026), Research Grants Council of Hong Kong (no. C1018-17G) and supported by Max-Planck-Gesellschaft (Max Planck Partner Group UESTC-MPIP) and the ERC advanced grant 340391-SUPRO. We thank S. J. Lin for assistance with adhesion force measurements; L. Zhou and T. H. Zhang for assistance with the analytical model; and S. Sun and H. L. Liu for discussions.
The authors declare no competing interests.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary Video legends 1–10, discussion, Figs. 1–14, Tables 1–4 and refs. 1–35.
Droplet transport mediated by surface charge gradient.
Droplet transport on a superamphiphobic surface with the SCD gradient placed upside down.
SCD gradient generation process.
Circular arc motion of a droplet.
Droplet transport on flexible superamphiphobic surfaces with SCD gradients.
Ultralong-distance droplet transport.
A droplet cargo device.
Charged surface-based droplet pipette.
Blood transportation with a SCD gradient.
Open channel droplet manipulation platform for particle transport.