Scalar Active Mixtures: The Nonreciprocal Cahn-Hilliard Model

Pair interactions between active particles need not follow Newton’s third law. In this work, we propose a continuum model of pattern formation due to nonreciprocal interaction between multiple species of scalar active matter. The classical Cahn-Hilliard model is minimally modified by supplementing t...

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Bibliographic Details
Published inPhysical review. X Vol. 10; no. 4; p. 041009
Main Authors Saha, Suropriya, Agudo-Canalejo, Jaime, Golestanian, Ramin
Format Journal Article
LanguageEnglish
Published College Park American Physical Society 01.10.2020
Subjects
Asymmetry
Chemical potential
Communication
Continuum modeling
Density
Equilibrium
Free energy
Molecular motors
Ostwald ripening
Phase separation
Symmetry
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Summary:Pair interactions between active particles need not follow Newton’s third law. In this work, we propose a continuum model of pattern formation due to nonreciprocal interaction between multiple species of scalar active matter. The classical Cahn-Hilliard model is minimally modified by supplementing the equilibrium Ginzburg-Landau dynamics with particle-number-conserving currents, which cannot be derived from a free energy, reflecting the microscopic departure from action-reaction symmetry. The strength of the asymmetry in the interaction determines whether the steady state exhibits a macroscopic phase separation or a traveling density wave displaying global polar order. The latter structure, which is equivalent to an active self-propelled smectic phase, coarsens via annihilation of defects, whereas the former structure undergoes Ostwald ripening. The emergence of traveling density waves, which is a clear signature of broken time-reversal symmetry in this active system, is a generic feature of any multicomponent mixture with microscopic nonreciprocal interactions.
ISSN:2160-3308
2160-3308
DOI:10.1103/PhysRevX.10.041009