Flow-induced nonequilibrium self-assembly in suspensions of stiff, apolar, active filaments

Pandey, Ankita; Kumar, P. B. Sunil; Adhikari, R.

doi:10.48550/arxiv.1408.0433

Cited by 4 publications

(11 citation statements)

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“…in these simulations R1 would rotate clockwise, R2 counter-clockwise). The formation of T-shaped swimmers was also predicted by these simulations, but for particles surrounded by contractile flows [16]. Notably, he T-swimmers in our experiments were formed from particles inducing extensile flows in their surroundings and ordered assemblies were not observed to form in experi-ments using particles with contractile flows.…”

Section: Discussionsupporting

confidence: 77%

“…Experiments of silver nanorods surrounded by contractile flows (the reverse of those studied here), induced by an external electric field that also aligns the nanorods, found evidence of hydrodynamic pair interactions [14]. Theoretical studies of 'extensors' have indicated the presence of interesting collective behaviour [15,16]. In the case of individually immotile particles, motility itself can be a signature of emergent dynamics as it indicates some form of symmetry breaking in the system.…”

Section: System and Phenomenologymentioning

confidence: 87%

“…The formation of both rotors and T-swimmers from symmetric active particles have been reported in a computational simulations of filaments constructed of active beads producing force-free, torque-free flows in a fluid, confined to move in 2D in an infinite domain [16]. Filaments surrounded by an overall extensile flow (similar to what is expected for the rods studied here) formed into parallel pairs which rotate, but in the opposite direction to that which is observed in our experiments (i.e.…”

Section: Discussionmentioning

confidence: 99%

“…The assembly of rods may be influenced by many physical effects, including hydrodynamic, electric, thermal and steric interactions. For the extensile rods studied here, simulations indicate that hydrodynamics alone is sufficient to bring together pairs of parallel rods [16]. To examine the effect of the flow surrounding the rod, experiments were conducted using rods of the alternative configuration, Pt-Au-Pt.…”

Section: Self-assemblymentioning

confidence: 99%

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Dynamic self-assembly of microscale rotors and swimmers

et al. 2016

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Biological systems often involve the self-assembly of basic components into complex and functioning structures. Artificial systems that mimic such processes can provide a well-controlled setting to explore the principles involved and also synthesize useful micromachines. Our experiments show that immotile, but active, components self-assemble into two types of structure that exhibit the fundamental forms of motility: translation and rotation. Specifically, micron-scale metallic rods are designed to induce extensile surface flows in the presence of a chemical fuel; these rods interact with each other and pair up to form either a swimmer or a rotor. Such pairs can transition reversibly between these two configurations, leading to kinetics reminiscent of bacterial run-and-tumble motion.Self-assembly is a hallmark of biological systems as organisms construct functional complex materials and structures from simpler components. The use of selfassembly in the fabrication of new materials is attractive owing to its inherent versatility and potential for mass production [1]. Research has focused primarily on systems where the formation of macrostructures does not require the continuous input of energy [2-5], a process known as equilibrium self-assembly. Another route to self-assembly is dynamic: where structures persist only while energy is being supplied to the system [6]. Artificial micron-scale motors, immersed in a fuel laden fluid, have been shown to spontaneously self-organize into crystal structures [7], and form into asters of two or more particles [8]. These studies have active components, producing a local fluid flow which leads to motility. A striking aspect of these active systems is their potential for emergent dynamics, whereby individuals and groups have qualitatively different behaviour [9], such as flocking [10], formation of flow structures on larger scales than the individual components [11], or collective flows which are faster than those induced by individual active particles [12].Here we describe how two of the simplest machines can be formed by dynamic self-assembly from a single type of building block. Active, but immotile, rods spontaneously self-assemble into structures that exhibit the two fundamental types of motion: rotation and translation ( Fig. 1d-g). This occurs without imposing any external field. Assemblies can transition between rotor and swimmer, leading to behaviour reminiscent of the run-and-tumble motion of E. coli [13]. The type and direction of motion is determined by the configuration of rods in an assembly, thereby linking the self-assembly to the emergent motility. This is a rare example of artificial dynamic self-assembly and therefore represents an important step towards making more complex micron-scale machines.

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Section: Discussionsupporting

confidence: 77%

Section: System and Phenomenologymentioning

confidence: 87%

Section: Discussionmentioning

confidence: 99%

Section: Self-assemblymentioning

confidence: 99%

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Dynamic self-assembly of microscale rotors and swimmers

et al. 2016

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“…Therefore, self-propulsion, also in combination with swimmer shape and interactions, can generate self-assembled bound states of active colloids, which autonomously translate and rotate depending on the specific shape of the assembled clusters [186,[273][274][275][276][277]. Interestingly, recent theoretical works indeed suggest the importance of swimmer shape, surface chemistry, and hydrodynamic interactions for the structures formed by self-assembled active colloids [278][279][280][281][282][283]. [12] (adapted with permission from Ref.…”

Section: Bound States and Self-assembly Of Active Colloidsmentioning

confidence: 99%

Emergent behavior in active colloids

Zöttl

Stark

2016

J. Phys.: Condens. Matter

528

559

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Active colloids are microscopic particles, which self-propel through viscous fluids by converting energy extracted from their environment into directed motion. We first explain how articial microswimmers move forward by generating near-surface flow fields via self-phoresis or the self-induced Marangoni effect. We then discuss generic features of the dynamics of single active colloids in bulk and in confinement, as well as in the presence of gravity, field gradients, and fluid flow. In the third part, we review the emergent collective behavior of active colloidal suspensions focussing on their structural and dynamic properties. After summarizing experimental observations, we give an overview on the progress in modeling collectively moving active colloids. While active Brownian particles are heavily used to study collective dynamics on large scales, more advanced methods are necessary to explore the importance of hydrodynamic and phoretic particle interactions. Finally, the relevant physical approaches to quantify the emergent collective behavior are presented.

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Brownian microhydrodynamics of active filaments

Laskar

Adhikari

2015

Soft Matter

Self Cite

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Slender bodies capable of spontaneous motion in the absence of external actuation in an otherwise quiescent fluid are common in biological, physical and technological contexts. The interplay between the spontaneous fluid flow, Brownian motion, and the elasticity of the body presents a challenging fluid-structure interaction problem. Here, we model this problem by approximating the slender body as an elastic filament that can impose non-equilibrium velocities or stresses at the fluid-structure interface. We derive equations of motion for such an active filament by enforcing momentum conservation in the fluid-structure interaction and assuming slow viscous flow in the fluid. The fluid-structure interaction is obtained, to any desired degree of accuracy, through the solution of an integral equation. A simplified form of the equations of motion, that allows for efficient numerical solutions, is obtained by applying the Kirkwood-Riseman superposition approximation to the integral equation. We use this form of the equation of motion to study dynamical steady states in free and hinged minimally active filaments. Our model provides the foundation to study collective phenomena in momentum-conserving, Brownian, active filament suspensions.

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Flow-induced nonequilibrium self-assembly in suspensions of stiff, apolar, active filaments

Cited by 4 publications

References 0 publications

Dynamic self-assembly of microscale rotors and swimmers

Dynamic self-assembly of microscale rotors and swimmers

Emergent behavior in active colloids

Brownian microhydrodynamics of active filaments

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