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Published May 2018 | Published + Supplemental Material + Submitted
Journal Article Open

Anisotropic swim stress in active matter with nematic order


Active Brownian particles (ABPs) transmit a swim pressure II^(swim) = n ζD^(swim) to the container boundaries, where ζ is the drag coefficient, D^(swim) is the swim diffusivity and n is the uniform bulk number density far from the container walls. In this work we extend the notion of the isotropic swim pressure to the anisotropic tensorial swim stress σ^(swim) = - n ζD^(swim), which is related to the anisotropic swim diffusivity D^(swim). We demonstrate this relationship with ABPs that achieve nematic orientational order via a bulk external field. The anisotropic swim stress is obtained analytically for dilute ABPs in both 2D and 3D systems. The anisotropy, defined as the ratio of the maximum to the minimum of the three principal stresses, is shown to grow exponentially with the strength of the external field. We verify that the normal component of the anisotropic swim stress applies a pressure II^(swim) = -( σ^(swim) · n) · n on a wall with normal vector n, and, through Brownian dynamics simulations, this pressure is shown to be the force per unit area transmitted by the active particles. Since ABPs have no friction with a wall, the difference between the normal and tangential stress components—the normal stress difference—generates a net flow of ABPs along the wall, which is a generic property of active matter systems.

Additional Information

© 2018 The Author(s). Published by IOP Publishing Ltd on behalf of Deutsche Physikalische Gesellschaft. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 27 February 2018; Accepted 10 May 2018; Accepted Manuscript online 10 May 2018; Published 24 May 2018. This work is supported by NSF CBET-1437570. We also thank the support from Simons Foundation, Flatiron Institute.

Attached Files

Published - Yan_2018_New_J._Phys._20_053056.pdf

Submitted - 1803.02418.pdf

Supplemental Material - NJPaac3c5_suppdata.pdf


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August 19, 2023
October 18, 2023