Surface charge printing for programmed droplet transport

Abstract

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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Fig. 1: Droplet transport mediated by a printable SCD gradient.
Fig. 2: Charge characterization and charge density gradient formation.
Fig. 3: Self-propulsion mechanism and performance control.
Fig. 4: General applications of the charged superamphiphobic surface.

Data availability

The data that support the findings of this study are available from the corresponding authors on reasonable request.

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Acknowledgements

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.

Author information

Q.S., X.D. and Z.W. conceived the research and designed the experiments. X.D., Z.W. and H.-J.B. supervised the research. Q.S., D.W. and J.Z. carried out the experiment. Q.S. and Y.L. built the analytical models. All authors analysed the data. Q.S., S.Y., L.C., J.C. and D.V. interpreted the data. Q.S., X.D., Z.W., D.V. and H.-J.B. wrote the paper.

Correspondence to Zuankai Wang or Hans-Jürgen Butt or Xu Deng.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Video legends 1–10, discussion, Figs. 1–14, Tables 1–4 and refs. 1–35.

Supplementary Video 1

Droplet transport mediated by surface charge gradient.

Supplementary Video 2

Droplet transport on a superamphiphobic surface with the SCD gradient placed upside down.

Supplementary Video 3

SCD gradient generation process.

Supplementary Video 4

Circular arc motion of a droplet.

Supplementary Video 5

Droplet transport on flexible superamphiphobic surfaces with SCD gradients.

Supplementary Video 6

Ultralong-distance droplet transport.

Supplementary Video 7

A droplet cargo device.

Supplementary Video 8

Charged surface-based droplet pipette.

Supplementary Video 9

Blood transportation with a SCD gradient.

Supplementary Video 10

Open channel droplet manipulation platform for particle transport.

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