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Spontaneous Ratchet Currents and Transition Dynamics in Active Wetting

Noah Grodzinski1,*, Robert L. Jack1,2, and Michael E. Cates1

  • *Contact author: njbg2@cam.ac.uk, he/him/his
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Phys. Rev. Lett. 136, 257101 – Published 23 June, 2026

DOI: https://doi.org/10.1103/sq25-hfsb

Abstract

Self-propelled particles accumulate on repulsive barriers in so-called active wetting, whose relationship with equilibrium wetting remains unclear. Using an exact (noiseless) hydrodynamic framework for an active lattice gas, we show, using a slit geometry with periodic boundary conditions, that active matter exhibits both fully wet and partially wet states, with a critical wetting transition between them. Furthermore, we demonstrate the existence of a spontaneous-symmetry-breaking ratchet current in the partially wet state, leading to departure of the bulk densities from their binodal values and the emergence of a novel dynamical pathway for the full-to-partial wetting transition. We elucidate this modified dynamical pathway using a minimal model. The results, while establishing a direct connection between active and equilibrium wetting, also identify the nonequilibrium consequences of activity.

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Hydrodynamic theory of wetting by active particles

Noah Grodzinski, Michael E. Cates, and Robert L. Jack
Phys. Rev. E 113, 065423 (2026)

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References (67)

  1. M. C. Marchetti, J. F. Joanny, S. Ramaswamy, T. B. Liverpool, J. Prost, M. Rao, and R. A. Simha, Hydrodynamics of soft active matter, Rev. Mod. Phys. 85, 1143 (2013).
  2. S. Ramaswamy, The mechanics and statistics of active matter, Annu. Rev. Condens. Matter Phys. 1, 323 (2010).
  3. M. E. Cates and J. Tailleur, Motility-induced phase separation, Annu. Rev. Condens. Matter Phys. 6, 219 (2015).
  4. M. E. Cates and C. Nardini, Active phase separation: New phenomenology from non-equilibrium physics, Rep. Prog. Phys. 88, 056601 (2025).
  5. T. Vicsek, A. Czirók, E. Ben-Jacob, I. Cohen, and O. Shochet, Novel type of phase transition in a system of self-driven particles, Phys. Rev. Lett. 75, 1226 (1995).
  6. J. Toner and Y. Tu, Flocks, herds, and schools: A quantitative theory of flocking, Phys. Rev. E 58, 4828 (1998).
  7. J. Tailleur and M. E. Cates, Statistical mechanics of interacting run-and-tumble bacteria, Phys. Rev. Lett. 100, 218103 (2008).
  8. J. Elgeti, R. G. Winkler, and G. Gompper, Physics of microswimmers—single particle motion and collective behavior: A review, Rep. Prog. Phys. 78, 056601 (2015).
  9. M. E. Cates and J. Tailleur, When are active Brownian particles and run-and-tumble particles equivalent? Consequences for motility-induced phase separation, Europhys. Lett. 101, 20010 (2013).
  10. Y. Fily and M. C. Marchetti, Athermal phase separation of self-propelled particles with no alignment, Phys. Rev. Lett. 108, 235702 (2012).
  11. G. S. Redner, M. F. Hagan, and A. Baskaran, Structure and dynamics of a phase-separating active colloidal fluid, Phys. Rev. Lett. 110, 055701 (2013).
  12. P. Digregorio, D. Levis, A. Suma, L. F. Cugliandolo, G. Gonnella, and I. Pagonabarraga, Full phase diagram of active Brownian disks: From melting to motility-induced phase separation, Phys. Rev. Lett. 121, 098003 (2018).
  13. R. Wittkowski, A. Tiribocchi, J. Stenhammar, R. J. Allen, D. Marenduzzo, and M. E. Cates, Scalar ϕ4 field theory for active-particle phase separation, Nat. Commun. 5, 4351 (2014).
  14. E. Tjhung, C. Nardini, and M. E. Cates, Cluster phases and bubbly phase separation in active fluids: Reversal of the Ostwald process, Phys. Rev. X 8, 031080 (2018).
  15. Y. Ben Dor, S. Ro, Y. Kafri, M. Kardar, and J. Tailleur, Disordered boundaries destroy bulk phase separation in scalar active matter, Phys. Rev. E 105, 044603 (2022).
  16. P. Galajda, J. Keymer, P. Chaikin, and R. Austin, A wall of funnels concentrates swimming bacteria, J. Bacteriol. 189, 8704 (2007).
  17. C. O. Reichhardt and C. Reichhardt, Ratchet effects in active matter systems, Annu. Rev. Condens. Matter Phys. 8, 51 (2017).
  18. C. Bechinger, R. Di Leonardo, H. Löwen, C. Reichhardt, G. Volpe, and G. Volpe, Active particles in complex and crowded environments, Rev. Mod. Phys. 88, 045006 (2016).
  19. J. Stenhammar, R. Wittkowski, D. Marenduzzo, and M. E. Cates, Light-induced self-assembly of active rectification devices, Sci. Adv. 2, e1501850 (2016).
  20. O. Granek, Y. Kafri, M. Kardar, S. Ro, J. Tailleur, and A. Solon, Colloquium: Inclusions, boundaries, and disorder in scalar active matter, Rev. Mod. Phys. 96, 031003 (2024).
  21. M. Mangeat, S. Chakraborty, A. Wysocki, and H. Rieger, Stationary particle currents in sedimenting active matter wetting a wall, Phys. Rev. E 109, 014616 (2024).
  22. S. Das, G. Gompper, and R. G. Winkler, Confined active Brownian particles: Theoretical description of propulsion-induced accumulation, New J. Phys. 20, 015001 (2018).
  23. J. Elgeti and G. Gompper, Wall accumulation of self-propelled spheres, Europhys. Lett. 101, 48003 (2013).
  24. N. Sepúlveda and R. Soto, Wetting transitions displayed by persistent active particles, Phys. Rev. Lett. 119, 078001 (2017).
  25. N. Sepúlveda and R. Soto, Universality of active wetting transitions, Phys. Rev. E 98, 052141 (2018).
  26. L. Caprini, D. Breoni, A. Ldov, C. Scholz, and H. Löwen, Dynamical clustering and wetting phenomena in inertial active matter, Commun. Phys. 7, 343 (2024).
  27. A. Wysocki and H. Rieger, Capillary action in scalar active matter, Phys. Rev. Lett. 124, 048001 (2020).
  28. U. Thiele, What is active wetting?, arXiv:2602.10287.
  29. S. Douezan, K. Guevorkian, R. Naouar, S. Dufour, D. Cuvelier, and F. Brochard-Wyart, Spreading dynamics and wetting transition of cellular aggregates, Proc. Natl. Acad. Sci. U.S.A. 108, 7315 (2011).
  30. J. F. Joanny, K. Kruse, J. Prost, and S. Ramaswamy, The actin cortex as an active wetting layer, Eur. Phys. J. E 36, 52 (2013).
  31. E. Lauga, W. R. DiLuzio, G. M. Whitesides, and H. A. Stone, Swimming in circles: Motion of bacteria near solid boundaries, Biophys. J. 90, 400 (2006).
  32. L. Chai, V. Zaburdaev, and R. Kolter, How bacteria actively use passive physics to make biofilms, Proc. Natl. Acad. Sci. U.S.A. 121, e2403842121 (2024).
  33. R. M. Harshey, Bacterial motility on a surface: Many ways to a common goal, Annu. Rev. Microbiol. 57, 249 (2003).
  34. C. Pérez-González, R. Alert, C. Blanch-Mercader, M. Gómez-González, T. Kolodziej, E. Bazellieres, J. Casademunt, and X. Trepat, Active wetting of epithelial tissues, Nat. Phys. 15, 79 (2019).
  35. A. Brugués, E. Anon, V. Conte, J. H. Veldhuis, M. Gupta, J. Colombelli, J. J. Muñoz, G. W. Brodland, B. Ladoux, and X. Trepat, Forces driving epithelial wound healing, Nat. Phys. 10, 683 (2014).
  36. K. Binder and D. P. Landau, Wetting and layering in the nearest-neighbor simple-cubic Ising lattice: A Monte Carlo investigation, Phys. Rev. B 37, 1745 (1988).
  37. P. G. de Gennes, Wetting: Statics and dynamics, Rev. Mod. Phys. 57, 827 (1985).
  38. D. E. Sullivan and M. M. Telo da Gama, Wetting transitions and multilayer adsorption at fluid interfaces, in Fluid Interfacial Phenomena, edited by C. A. Croxton (Wiley, New York, 1986), pp. 45–134.
  39. S. Dietrich, Wetting phenomena, in Phase Transitions and Critical Phenomena, edited by C. Domb and J. L. Lebowitz (Academic Press, New York, 1988), Vol. 12.
  40. M. Schick, An introduction to wetting phenomena, in Liquids at Interfaces, Les Houches Summer School Session XLVIII, edited by J. Charvolin, J.-F. Joanny, and J. Zinn-Justin (North-Holland, Amsterdam, 1990), pp. 415–497.
  41. D. Bonn, J. Eggers, J. Indekeu, J. Meunier, and E. Rolley, Wetting and spreading, Rev. Mod. Phys. 81, 739 (2009).
  42. F. Turci, R. L. Jack, and N. B. Wilding, Partial and complete wetting of droplets of active Brownian particles, Soft Matter 20, 2060 (2024).
  43. Y. Zhao, R. Zakine, A. Daerr, Y. Kafri, J. Tailleur, and F. van Wijland, Wetting by active fluids, Nat. Phys. 22, 805 (2026).
  44. P. D. Neta, M. Tasinkevych, M. M. Telo da Gama, and C. S. Dias, Wetting of a solid surface by active matter, Soft Matter 17, 2468 (2021).
  45. F. Turci and N. B. Wilding, Wetting transition of active Brownian particles on a thin membrane, Phys. Rev. Lett. 127, 238002 (2021).
  46. S. Das and R. Chelakkot, Morphological transitions of active Brownian particle aggregates on porous walls, Soft Matter 16, 7250 (2020).
  47. P. Pérez-Bastías and R. Soto, Two-field theory for phase coexistence of active Brownian particles, Phys. Rev. E 112, 055403 (2025).
  48. S. Das and R. Chelakkot, Active wetting transitions induced by rotational noise at solid interfaces, J. Chem. Phys. 163, 014704 (2025).
  49. N. Grodzinski, M. E. Cates, and R. L. Jack, Hydrodynamic theory of wetting by active particles, Phys. Rev. E 113, 065423 (2026).
  50. J. Bialké, J. T. Siebert, H. Löwen, and T. Speck, Negative interfacial tension in phase-separated active Brownian particles, Phys. Rev. Lett. 115, 098301 (2015).
  51. R. Adkins, I. Kolvin, Z. You, S. Witthaus, M. C. Marchetti, and Z. Dogic, Dynamics of active liquid interfaces, Science 377, 768 (2022).
  52. R. Zakine, Y. Zhao, M. Knežević, A. Daerr, Y. Kafri, J. Tailleur, and F. van Wijland, Surface tensions between active fluids and solid interfaces: Bare vs dressed, Phys. Rev. Lett. 124, 248003 (2020).
  53. M. Kourbane-Houssene, C. Erignoux, T. Bodineau, and J. Tailleur, Exact hydrodynamic description of active lattice gases, Phys. Rev. Lett. 120, 268003 (2018).
  54. J. Mason, C. Erignoux, R. L. Jack, and M. Bruna, Exact hydrodynamics and onset of phase separation for an active exclusion process, Proc. R. Soc. A 479, 20230524 (2023).
  55. C. Erignoux, On the hydrodynamics of active matter models on a lattice, Markov Proc. Relat. Fields 30, 57 (2024).
  56. J. Mason, R. L. Jack, and M. Bruna, Macroscopic behaviour in a two-species exclusion process via the method of matched asymptotics, J. Stat. Phys. 190, 47 (2023).
  57. R. Evans, M. C. Stewart, and N. B. Wilding, A unified description of hydrophilic and superhydrophobic surfaces in terms of the wetting and drying transitions of liquids, Proc. Natl. Acad. Sci. U.S.A. 116, 23901 (2019).
  58. J. M. J. van Leeuwen, M. J. P. Nijmeijer, and C. Bruin, Molecular dynamics of wetting and drying at solid-fluid interfaces, Phys. Scr. 1989, 256 (1989).
  59. J. H. Sikkenk, J. O. Indekeu, J. M. J. van Leeuwen, and E. O. Vossnack, Molecular-dynamics simulation of wetting and drying at solid-fluid interfaces, Phys. Rev. Lett. 59, 98 (1987).
  60. M. J. P. Nijmeijer, C. Bruin, A. F. Bakker, and J. M. J. van Leeuwen, Wetting and drying of an inert wall by a fluid in a molecular-dynamics simulation, Phys. Rev. A 42, 6052 (1990).
  61. J. W. Cahn, Critical point wetting, J. Chem. Phys. 66, 3667 (1977).
  62. J. Metzger, S. Ro, and J. Tailleur, Exceptions to the ratchet principle in active and passive stochastic dynamics, arXiv:2503.11902.
  63. J. Palacci, S. Sacanna, S.-H. Kim, G.-R. Yi, D. J. Pine, and P. M. Chaikin, Light-activated self-propelled colloids, Phil. Trans. R. Soc. A 372, 20130372 (2014).
  64. I. Buttinoni, J. Bialké, F. Kümmel, H. Löwen, C. Bechinger, and T. Speck, Dynamical clustering and phase separation in suspensions of self-propelled colloidal particles, Phys. Rev. Lett. 110, 238301 (2013).
  65. A. Fins Carreira, A. Wysocki, C. Ybert, M. Leocmach, H. Rieger, and C. Cottin-Bizonne, How to steer active colloids up a vertical wall, Nat. Commun. 15, 1710 (2024).
  66. N. Grodzinski, Research data supporting hydrodynamic theory of wetting by active particles and spontaneous ratchet currents and transition dynamics in active wetting, 10.17863/CAM.129364 (2026).
  67. J. Sherman and W. J. Morrison, Adjustment of an inverse matrix corresponding to a change in one element of a given matrix, Ann. Math. Stat. 21, 124 (1950).

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Phys. Rev. Lett. 136, 257101– Published 23 June, 2026
  • Received 26 December 2025
  • Accepted 6 April 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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