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Anisotropic swim stress in active matter with nematic order
Active Brownian Particles (ABPs) transmit a swim pressure to the container boundaries, where is the drag coefficient,
is the swim diffusivity and 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
, which is related to the
anisotropic swim diffusivity . 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, and the anisotropy 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
on a wall
with normal vector , 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
Anti-Swarming: Structure and Dynamics of Repulsive Chemically Active Particles
Chemically active Brownian particles with surface catalytic reactions may
repel each other due to diffusiophoretic interactions in the reaction and
product concentration fields. The system behavior can be described by a
`chemical' coupling parameter that compares the strength of
diffusiophoretic repulsion to Brownian motion, and by a mapping to the
classical electrostatic One Component Plasma (OCP) system. When confined to a
constant-volume domain, Body-Centered Cubic crystals spontaneously form from
random initial configurations when the repulsion is strong enough to overcome
Brownian motion. Face-Centered Cubic crystals may also be stable. The `melting
point' of the `liquid-to-crystal transition' occurs at for
both BCC and FCC lattices
The curved kinetic boundary layer of active matter
The finite reorient-time of swimmers leads to a finite run length and
the kinetic accumulation boundary layer on the microscopic length scale
on a non-penetrating wall. That boundary layer is the microscopic
origin of the swim pressure, and is impacted by the geometry of the boundary
[Yan \& Brady, \textit{J. Fluid. Mech.}, 2015, \textbf{785}, R1]. In this work
we extend the analysis to analytically solve the boundary layer on an
arbitrary-shaped body distorted by the local mean curvature. The solution gives
the swim pressure distribution and the total force (torque) on an arbitrarily
shaped body immersed in swimmers, with a general scaling of the curvature
effect
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