Eur. Phys. J. E (2012) 35: 115
https://doi.org/10.1140/epje/i2012-12115-9

Regular Article

Instabilities and diffusion in a hydrodynamic model of a fluid membrane coupled to a thin active fluid layer

Theoretical Condensed Matter Physics Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, 700 064, Calcutta, India

^* e-mail: niladri.sarkar@saha.ac.in

Received: 2 August 2011
Accepted: 19 September 2012
Published online: 13 November 2012

Abstract

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.