Active colloids in liquid crystals

Lavrentovich, Oleg D.

doi:10.1016/j.cocis.2015.11.008

Cited by 102 publications

(92 citation statements)

References 98 publications

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“…Kink walls (KW): Upon increasing activity, the magnitude of S decreases and director deformations become larger, acquiring a splay character (see movies S2 and S5 in SI). The system organizes in a structure of parallel kink walls, with largescale smectic order, resembling the patterns seen in living liquid crystals of B. subtilis swimming in a passive nematic 10,46 . The width and spacing of the kink walls is set by the length scale Fig.…”

Section: Ordered State -R >mentioning

confidence: 99%

Negative stiffness and modulated states in active nematics

2016

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We examine the dynamics of an active nematic liquid crystal on a frictional substrate. When frictional damping dominates over viscous dissipation, we eliminate flow in favor of active stresses to obtain a minimal dynamical model for the nematic order parameter, with elastic constants renormalized by activity. The renormalized elastic constants can become negative at large activity, leading to the selection of spatially inhomogeneous patterns via a mechanism analogous to that responsible for modulated phases arising at an equilibrium Lifshitz point. Tuning activity and the degree of nematic order in the passive system, we obtain a linear stability phase diagram that exhibits a nonequilibrium tricritical point where ordered, modulated and disordered phases meet. Numerical solution of the nonlinear equations yields a succession of spatial structures of increasing complexity with increasing activity, including kink walls and active turbulence, as observed in experiments on microtubule bundles confined at an oil-water interface. Our work provides a minimal model for an overdamped active nematic that reproduces all the nonequilibrium structures seen in simulations of the full active nematic hydrodynamics and provides a framework for understanding some of the mechanisms for selection of the nonequilibrium patterns in the language of equilibrium critical phenomena.Active systems are continuously driven out of equilibrium by energy injected at the local scale and generate collective motion at the large scale. Examples include bacterial colonies, in vitro extracts of cytoskeletal filaments and motor proteins, and living cells 1 . Elongated active particles can order in states with liquid crystalline order. The emergent behavior of such 'living' liquid crystals has been described using liquid crystal hydrodynamics, modified to include the local energy input from active processes 2,3 . This work has highlighted a rich variety of collective phenomena, including spontaneous laminar flow, pattern formation, spontaneous unbinding of topological defects, and active turbulence 4-13 . Previous studies have established that bulk active nematics are generically unstable 1,3,14,15 . Confinement, on the other hand, has profound effects on active fluids. It damps the flow 16,17 and suppresses the generic instability of unbound systems, resulting in a finite activity threshold for the onset of spontaneously flowing states 8,18 . Frictional damping due to confinement plays a key role in experimental realizations of active systems. In bacterial suspensions channel confinement was shown to stabilize vortex In confined nematics the energy input from active stresses is dissipated both via viscous flows that mediate hydrodynamic interactions between the active units and via friction with a substrate. Systems where viscous dissipation dominates so that frictional damping is negligible and momentum is conserved are referred to as 'wet', while those where dissipation is mainly controlled by friction are referred to as 'dry'. Previous work has ex...

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Section: Ordered State -R >mentioning

confidence: 99%

Negative stiffness and modulated states in active nematics

2016

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“…Microscale manipulation of colloidal particles and fluids by electric fields is a broad area of active scientific research ranging from fundamental studies of non-equilibrium phenomena [1][2][3][4] to the development of practical devices for informational displays, portable diagnostics, sensing, delivery, and sorting [5][6][7]. It has been demonstrated recently [4,[8][9][10] that when a nematic liquid crystal is used as an electrolyte instead of an isotropic fluid, electrokinetic phenomena acquire qualitatively new characteristics.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear Electrophoresis of Colloids Controlled by Anisotropic Conductivity and Permittivity of Liquid-Crystalline Electrolyte

et al. 2017

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Liquid crystal electrolytes enable nonlinear electrophoresis of colloidal particles with velocities proportional to the square of the applied field. We demonstrate that the magnitude and even the polarity of electrophoretic mobility can be controlled by the anisotropy of electric conductivity and dielectric permittivity of the liquid crystal. In particular, reversal of electrophoretic mobility can be triggered either by temperature or composition changes that alter the signs of the conductivity and permittivity anisotropies. Controllable reversal of mobility adds to the list of advantages of anisotropic electrolytes over their isotropic counterparts. † olavrent@kent.edu

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“…The onset of Quincke rotation in suspensions can lead to several remarkable effects such as effective viscosity reduction [5,6] and increased effective electric conductivity of suspensions [7]. Quincke rotating colloidal particles have been observed to "roll" with a constant velocity on surfaces in liquid crystals and on bubbles [8]. A system of many such interacting self-propelled Quincke rotors has served as a model system for collective swarming motion and active matter [9].…”

Section: Introductionmentioning

confidence: 99%

Electro-hydrodynamic propulsion of counter-rotating Pickering drops

Dommersnes

Mikkelsen

Fossum

2016

Eur. Phys. J. Spec. Top.

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Insulating particles or drops suspended in carrier liquids may start to rotate with a constant frequency when subjected to a uniform DC electric field. This is known as the Quincke rotation electro-hydrodynamic instability. A single isolated rotating particle exhibit no translational motion at low Reynolds number, however interacting rotating particles may move relative to one another. Here we present a simple system consisting of two interacting and deformable Quincke rotating particle covered drops, i.e. deformable Pickering drops. The drops attract one another and spontaneously form a counter-rotating pair that exhibits electro-hydrodynamic driven propulsion at low Reynolds number flow.

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Active colloids in liquid crystals

Cited by 102 publications

References 98 publications

Negative stiffness and modulated states in active nematics

Negative stiffness and modulated states in active nematics

Nonlinear Electrophoresis of Colloids Controlled by Anisotropic Conductivity and Permittivity of Liquid-Crystalline Electrolyte

Electro-hydrodynamic propulsion of counter-rotating Pickering drops

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