Motility of active nematic films driven by “active anchoring”

Blow, Matthew L.; Aqil, Marco; Liebchen, Benno; Marenduzzo, Davide

doi:10.1039/c7sm00325k

Cited by 25 publications

(25 citation statements)

References 33 publications

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“…The instability is driven by the active force that increases with the interfacial curvature which in turn increases the curvature of the interfaces with planar anchoring. This instability is closely related to the bend instability for extensile systems reported previously in unconfined active nematic emulsions 25,27 . With one important difference: the active force that drives the interfacial instability is also responsible for the re-appearence of the nematic phase and the interfacial state persists at long times.…”

Section: Flow States and Interfacial Instabilitysupporting

confidence: 81%

Active nematic–isotropic interfaces in channels

2019

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We use numerical simulations to investigate the hydrodynamic behavior of the interface between nematic (N) and isotropic (I) phases of a confined active liquid crystal. At low activities, a stable interface with constant shape and velocity is observed separating the two phases. For nematics in homeotropic channels, the velocity of the interface at the NI transition increases from zero (i) linearly with the activity for contractile systems and (ii) quadratically for extensile ones. Interestingly, the nematic phase expands for contractile systems while it contracts for extensile ones, as a result of the active forces at the interface. Since both activity and temperature affect the stability of the nematic, for active nematics in the stable regime the temperature can be tuned to observe static interfaces, providing an operational definition for the coexistence of active nematic and isotropic phases. At higher activities, beyond the stable regime, an interfacial instability is observed for extensile nematics. In this regime defects are nucleated at the interface and move away from it. The dynamics of these defects is regular and persists asymptotically for a finite range of activities. We used an improved hybrid model of finite differences and lattice Boltzmann method with multirelaxation-time collision operator, the accuracy of which allowed us to characterize the dynamics of the distinct interfacial regimes.

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Section: Flow States and Interfacial Instabilitysupporting

confidence: 81%

Active nematic–isotropic interfaces in channels

2019

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“…By contrast, active anchoring has been reported only recently in the context of active matter, which refers to systems composed of interacting particles that generate motion through the supply of energy at the particle level [3,4]. A range of biological systems including suspensions of swimming bacteria [5–7] belong to this class, which is characterized by novel intrinsically non-equilibrium phenomena with some degree of universality.…”

Section: Introductionmentioning

confidence: 99%

“…Typically, active systems exhibit collective complex motion including turbulence at low Reynolds number. Interfaces of these systems, such as in active droplets and films, have been reported to exhibit instabilities which are different from those of the bulk [3,4,8]. The conditions under which these instabilities may lead to spontaneous motion of the bulk fluid are not yet completely understood.…”

Section: Introductionmentioning

confidence: 99%

Director alignment at the nematic–isotropic interface: elastic anisotropy and active anchoring

Coelho

Araújo

Gama

2021

Phil. Trans. R. Soc. A.

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Activity in nematics drives interfacial flows that lead to preferential alignment that is tangential or planar for extensile systems (pushers) and perpendicular or homeotropic for contractile ones (pullers). This alignment is known as active anchoring and has been reported for a number of systems and described using active nematic hydrodynamic theories. The latter are based on the one-elastic constant approximation, i.e. they assume elastic isotropy of the underlying passive nematic. Real nematics, however, have different elastic constants, which lead to interfacial anchoring. In this paper, we consider elastic anisotropy in multiphase and multicomponent hydrodynamic models of active nematics and investigate the competition between the interfacial alignment driven by the elastic anisotropy of the passive nematic and the active anchoring. We start by considering systems with translational invariance to analyse the alignment at flat interfaces and, then, consider two-dimensional systems and active nematic droplets. We investigate the competition of the two types of anchoring over a wide range of the other parameters that characterize the system. The results of the simulations reveal that the active anchoring dominates except at very low activities, when the interfaces are static. In addition, we found that the elastic anisotropy does not affect the dynamics but changes the active length that becomes anisotropic. This article is part of the theme issue ‘Progress in mesoscale methods for fluid dynamics simulation’.

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“…It is worth to mention that this self-organized trapping is qualitatively different from motility-induced phase separation, which occurs in homogeneous motility fields [28], and from capturing self-propelled rods in wedge-like obstacles where the trapping is induced by geometry [29][30][31]. Moreover the active membranes found here are different from active nematic films driven by anchoring and patterning [32][33][34].…”

Section: Introductionmentioning

confidence: 47%

Spontaneous membrane formation and self-encapsulation of active rods in an inhomogeneous motility field

2018

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We study the collective dynamics of self-propelled rods in an inhomogeneous motility field. At the interface between two regions of constant but different motility, a smectic rod layer is spontaneously created through aligning interactions between the active rods, reminiscent of an artificial, semi-permeable membrane. This "active membrane" engulfes rods which are locally trapped in low-motility regions and thereby further enhances the trapping efficiency by self-organization, an effect which we call "self-encapsulation". Our results are gained by computer simulations of self-propelled rod models confined on a two-dimensional planar or spherical surface with a stepwise constant motility field, but the phenomenon should be observable in any geometry with sufficiently large spatial inhomogeneity. We also discuss possibilities to verify our predictions of active-membrane formation in experiments of self-propelled colloidal rods and vibrated granular matter.

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Motility of active nematic films driven by “active anchoring”

Cited by 25 publications

References 33 publications

Active nematic–isotropic interfaces in channels

Active nematic–isotropic interfaces in channels

Director alignment at the nematic–isotropic interface: elastic anisotropy and active anchoring

Spontaneous membrane formation and self-encapsulation of active rods in an inhomogeneous motility field

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