https://doi.org/10.1140/epje/s10189-025-00508-0
Regular Article - Flowing Matter
The effect of self-induced Marangoni flow on polar-nematic waves in active-matter systems
1
Department of Mathematics, Swinburne University of Technology, John Street, 3122, Hawthorn, VIC, Australia
2
Institute for Theoretical Physics, University of Münster, Wilhelm-Klemm-Str. 9, 48149, Münster, Germany
3
Center for Nonlinear Science (CeNoS), University of Münster, Corrensstr. 2, 48149, Münster, Germany
4
Center for Multiscale Theory and Computation (CMTC), University of Münster, Corrensstr. 40, 48149, Münster, Germany
Received:
5
March
2025
Accepted:
3
July
2025
Published online:
30
July
2025
We study the formation of propagating large-scale density waves of mixed polar-nematic symmetry in a colony of self-propelled agents that are bound to move along the planar surface of a thin viscous film. The agents act as an insoluble surfactant, i.e. the surface tension of the liquid depends on their density. Therefore, density gradients generate a Marangoni flow. We demonstrate that for active matter in the form of self-propelled surfactants with local (nematic) aligning interactions such a Marangoni flow nontrivially influences the propagation of the density waves. Upon gradually increasing the Marangoni parameter, which characterises the relative strength of the Marangoni flow as compared to the self-propulsion speed, the density waves broaden while their speed may either increase or decrease depending on wavelength and overall mean density. A further increase in the Marangoni parameter eventually results in the disappearance of the density waves. This may occur either discontinuously at finite wave amplitude via a saddle-node bifurcation or continuously with vanishing wave amplitude at a wave bifurcation, i.e. a finite-wavelength Hopf bifurcation.
© The Author(s) 2025
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