Motility of active fluid drops on surfaces

Abstract

Drops of active liquid crystal have recently shown the ability to self-propel, which was associated with topological defects in the orientation of active filaments [Sanchez {\em et al.}, Nature {\bf 491}, 431 (2013)]. Here, we study the onset and different aspects of motility of a three-dimensional drop of active fluid on a planar surface. We analyse theoretically how motility is affected by orientation profiles with defects of various types and locations, by the shape of the drop, and by surface friction at the substrate. In the scope of a thin drop approximation, we derive exact expressions for the flow in the drop that is generated by a given orientation profile. The flow has a natural decomposition into terms that depend entirely on the geometrical properties of the orientation profile, i.e. its bend and splay, and a term coupling the orientation to the shape of the drop. We find that asymmetric splay or bend generates a directed bulk flow and enables the drop to move, with maximal speeds achieved when the splay or bend is induced by a topological defect in the interior of the drop. In motile drops the direction and speed of self-propulsion is controlled by friction at the substrate.

arXiv comment11 pages, 8 figures

References in corpus (20)

• The Mechanics and Statistics of Active Matter
• Spontaneous motion in hierarchically assembled active matter
• Hydrodynamic fluctuations and instabilities in ordered suspensions of self-propelled particles
• Topology and Dynamics of Active Nematic Vesicles
• Rheology of Active-Particle Suspensions
• Generic theory of active polar gels: a paradigm for cytoskeletal dynamics
• Confinement Stabilizes a Bacterial Suspension into a Spiral Vortex
• Fluid Flows Created by Swimming Bacteria Drive Self-Organization in Confined Suspensions
• Defect annihilation and proliferation in active nematics
• Defect dynamics in active nematics
• Spontaneous symmetry breaking in active droplets provides a generic route to motility
• Spontaneous Circulation of Confined Active Suspensions
• Spontaneous contractility--mediated cortical flow generates cell migration in 3-dimensional environments
• Spontaneous division and motility in active nematic droplets
• A minimal physical model captures the shapes of crawling cells
• A Drop of Active Matter
• Instabilities and waves in thin films of living fluids
• Do liquid drops roll or slide on inclined surfaces?
• A mechanism for cell motility by active polar gels
• Active polar fluid flow in finite droplets

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