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Wetting by active fluids

Nature Physics (2026)Cite this article

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Abstract

The Young–Dupré equation is a cornerstone of the theory of capillary and wetting phenomena, which governs the shape of droplets adsorbed on surfaces in equilibrium. However, many living and synthetic materials, such as swarming bacteria and active colloids, are composed of self-propelled particles that are inherently out of thermal equilibrium. The description of the wetting of surfaces by such active fluids thus requires a new framework. Here we develop an analogue to the Young–Dupré equation for systems made of self-propelled particles. A key step is to define the liquid–gas surface tension of active fluids as the force exerted along the interface, which we show from first principles to be negative, even when active materials separate into stable liquid and gas phases. Our active Young–Dupré equation explains why partial wetting appears in simulations where the surface tensions do not balance and reveals the underlying feedback mechanism: the interface is stable only because of steady flows, which are themselves generated by the parity symmetry-breaking interface. Unlike in passive fluids, where the droplets are scale-free, this feedback loop selects the sizes and shapes of adsorbed droplets in active materials. Our results outline a framework for understanding how active matter wets surfaces.

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Fig. 1: Wetting of a solid surface by a macroscopic liquid droplet.
Fig. 2: When interfaces exert active surface (ex)tension on confining walls.
Fig. 3: The active Young–Dupré equation.
Fig. 4: Size selection and splitting dynamics of active droplets adsorbed on a solid surface.

Data availability

The data that support the findings of this study are available from the corresponding author upon request. The data generated in this study are available via Figshare at https://doi.org/10.6084/m9.figshare.31148908 (ref. 70).

Code availability

The codes and algorithms that have been used to support the findings of this study are available from the corresponding author upon request.

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Acknowledgements

F.v.W., J.T. and R.Z. thank K. Mandadapu at University of California Berkeley for hospitality and discussions. J.T. thanks the Laboratoire MSC for hospitality. Y.Z. acknowledges support from National Natural Science Foundation of China (grant no. 12304252). Y.K. acknowledges financial support from ISF (grant nos. 2038/21 and 3457/25) and NSF/BSF (grant no. 2022605). F.v.W. and J.T. acknowledge support from ANR Thema.

Author information

Authors and Affiliations

  1. Center for Soft Condensed Matter Physics and Interdisciplinary Research and School of Physical Science and Technology, Soochow University, Suzhou, China

    Yongfeng Zhao  (赵永峰)

  2. School of Physics and Astronomy and Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai, China

    Yongfeng Zhao  (赵永峰)

  3. Laboratoire d’Hydrodynamique, CNRS, École Polytechnique, Institut Polytechnique de Paris, Palaiseau, France

    Ruben Zakine

  4. Université Paris Cité, Laboratoire Matière et Systèmes Complexes, Paris, France

    Adrian Daerr & Frédéric van Wijland

  5. Department of Physics, Technion—Israel Institute of Technology, Haifa, Israel

    Yariv Kafri

  6. Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA

    Julien Tailleur

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  1. Yongfeng Zhao  (赵永峰)
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  2. Ruben Zakine
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  3. Adrian Daerr
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  6. Frédéric van Wijland
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Contributions

Y.Z., R.Z., A.D., J.T., Y.K. and F.v.W. conceived the project. Y.Z., A.D., J.T., Y.K. and F.v.W. wrote the manuscript. Y.Z. produced all numerical data.

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Correspondence to Yongfeng Zhao  (赵永峰).

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Nature Physics thanks Takumi Matsuzawa and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information (download PDF )

Supplementary Sections 1–12, Movies 1–7 and Figs. 1–14.

Supplementary Video 1 (download MP4 )

Wilhelmy plates being expelled from the active liquid phase.

Supplementary Video 2 (download MP4 )

Intermittent dynamics of active droplets.

Supplementary Video 3 (download MP4 )

A droplet of initial radius R0 = 175 showing the stability of macroscopic phase separation.

Supplementary Video 4 (download MP4 )

A droplet of initial radius R0 = 1,750 showing the stability of macroscopic phase separation.

Supplementary Video 5 (download MP4 )

Intermittent dynamics of adsorbed active droplets showing a reverse Ostwald ripening.

Supplementary Video 6 (download MP4 )

A system with bulk phase separation in a periodic system.

Supplementary Video 7 (download MP4 )

Intermittent dynamics of active droplets corresponding to Supplementary Fig. 9h.

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Zhao, Y., Zakine, R., Daerr, A. et al. Wetting by active fluids. Nat. Phys. (2026). https://doi.org/10.1038/s41567-026-03208-4

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