164 research outputs found
Instabilities and diffusion in a hydrodynamic model of a fluid membrane coupled to a thin active fluid layer
We construct a coarse-grained effective two-dimensional (2d) hydrodynamic
theory as a theoretical model for a coupled system of a fluid membrane and a
thin layer of a polar active fluid in its ordered state that is anchored to the
membrane. We show that such a system is prone to generic instabilities through
the interplay of nonequilibrium drive, polar order and membrane fluctuation. We
use our model equations to calculate diffusion coefficients of an inclusion in
the membrane and show that their values depend strongly on the system size, in
contrast to their equilibrium values. Our work extends the work of S.
Sankararaman and S. Ramaswamy [Phys. Rev. Lett., 102, 118107 (2009)] to a
coupled system of a fluid membrane and an ordered active fluid layer. Our model
is broadly inspired by and should be useful as a starting point for theoretical
descriptions of the coupled dynamics of a cell membrane and a cortical actin
layer anchored to it.Comment: accepted in EPJ
Generic instabilities in a fluid membrane coupled to a thin layer of ordered active polar fluid
We develop an effective two-dimensional coarse-grained description for the
coupled system of a planar fluid membrane anchored to a thin layer of polar
ordered active fluid below. The macroscopic orientation of the active fluid
layer is assumed to be perpendicular to the attached membrane. We demonstrate
that {\em activity} or nonequilibrium drive of the active fluid makes such a
system generically linearly unstable for either signature of a model parameter
that characterises the strength of activity. Depending upon
boundary conditions and within a range of the model parameters, underdamped
propagating waves may be present in our model. We discuss the phenomenological
significance of our results.Comment: 13 pages, accepted in EPJ
Role of interfacial friction for flow instabilities in a thin polar ordered active fluid layer
We construct a generic coarse-grained dynamics of a thin inflexible planar
layer of polar-ordered suspension of active particles, that is frictionally
coupled to an embedding isotropic passive fluid medium with a friction
coefficient . Being controlled by , our model provides a
unified framework to describe the long wavelength behaviour of a variety of
thin polar-ordered systems, ranging from {\em wet} to {\em dry} active matters
and free standing active films. Investigations of the linear instabilities
around a chosen orientationally ordered uniform reference state reveal generic
moving and static instabilities in the system, that can depend sensitively on
. Based on our results, we discuss estimation of bounds on in
experimentally accessible systems.Comment: 23 pages, to be published in PR
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