Bimetallic Microswimmers Speed Up in Confining Channels

Liu, Chang; Zhou, Chao; Wang, Wei; Zhang, Hepeng

doi:10.1103/physrevlett.117.198001

Cited by 90 publications

(75 citation statements)

References 63 publications

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“…Interestingly, the swimming speed increases as the robot arms are confined further by the floor and the walls. Similar results have been previously reported with different type of swimmers in confinement [7,[18][19][20][21][22][23][24][25]. For instance, a microswimmer modeled as an infinite waving sheet is able to swim faster near parallel walls with an increase in the rate of working by the sheet [18].…”

Section: Discussionsupporting

confidence: 88%

Metachronal Swimming with Rigid Arms near Boundaries

Hayashi

Takagi

2020

Fluids

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Various organisms such as crustaceans use their appendages for locomotion. If they are close to a confining boundary then viscous as opposed to inertial effects can play a central role in governing the dynamics. To study the minimal ingredients needed for swimming without inertia, we built an experimental system featuring a robot equipped with a pair of rigid slender arms with negligible inertia. Our results show that directing the arms to oscillate about the same time-averaged orientation produces no net displacement of the robot each cycle, regardless of any phase delay between the oscillating arms. The robot is able to swim if the arms oscillate asynchronously around distinct orientations. The measured displacement over time matches well with a mathematical model based on slender-body theory for Stokes flow. Near a confining boundary, the robot with no net displacement every cycle showed similar behavior, while the swimming robot increased in speed closer to the boundary.

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Section: Discussionsupporting

confidence: 88%

Metachronal Swimming with Rigid Arms near Boundaries

Hayashi

Takagi

2020

Fluids

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“…Our numerical and analytical calculations have considered a self-diffusiophoretic particle with a monopole term, i.e., a net producer of product molecules. However, our theoretical framework can also be applied to confined self-electrophoretic particles, under the additional assumption of the presence of a thin Debye layer required by a mapping to an osmotic slip velocity (which has been used in, e.g., [44]), with appropriate renaming of the variables: ( ) c x as an electrical potential y ( ) x , the surface mobility ( ) b x s as a quantity proportional to the zeta potential z ( ) x s , etc [19,31,44,45]. A selfelectrophoretic particle would have no monopole term (a = 0 0 ), but otherwise our findings would carry over to this new setting.…”

Section: Discussionmentioning

confidence: 99%

Shape-dependent guidance of active Janus particles by chemically patterned surfaces

et al. 2018

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Self-phoretic chemically active Janus particles move by inducing-via non-equilibrium chemical reactions occurring on their surfaces-changes in the chemical composition of the solution in which they are immersed. This process leads to gradients in chemical composition along the surface of the particle, as well as along any nearby boundaries, including solid walls. Chemical gradients along a wall can give rise to chemi-osmosis, i.e., the gradients drive surface flows which, in turn, drive flow in the volume of the solution. This bulk flow couples back to the particle, and thus contributes to its selfmotility. Since chemi-osmosis strongly depends on the molecular interactions between the diffusing molecular species and the wall, the response flow induced and experienced by a particle encodes information about any chemical patterning of the wall. Here, we extend previous studies on selfphoresis of a sphere near a chemically patterned wall to the case of particles with rod-like, elongated shape. We focus our analysis on the new phenomenology potentially emerging from the couplingwhich is inoperative for a spherical shape-of the elongated particle to the strain rate tensor of the chemi-osmotic flow. Via detailed numerical calculations, we show that the dynamics of a rod-like particle exhibits a novel 'edge-following' steady state: the particle translates along the edge of a chemical step at a steady distance from the step and with a steady orientation. Moreover, within a certain range of system parameters, the edge-following state co-exists with a 'docking' state (the particle stops at the step, oriented perpendicular to the step edge), i.e., a bistable dynamics occurs. These findings are rationalized as a consequence of the competition between the fluid vorticity and the rate of strain by using analytical theory based on the point-particle approximation which captures quasi-quantitatively the dynamics of the system.

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“…Narrow gaps may significantly change the swimming behavior of the self-propelled rods, which is not considered in our model. For example, experiments show that active rods can increase speed by up to five times in confining channels with ceiling [37]. Further, the size of the rods, which is ignored in our model, becomes important when they swim in confined spaces like narrow gaps.…”

Section: The Effect Of Post Spacingsmentioning

confidence: 99%

Directed Migration of Microscale Swimmers by an Array of Shaped Obstacles: Modeling and Shape Optimization

Tong

Shelley²

2018

SIAM J. Appl. Math.

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Achieving macroscopic directed migration of microscale swimmers in a fluid is an important step towards utilizing their autonomous motion. It has been experimentally shown that directed motion can be induced, without any external fields, by certain geometrically asymmetric obstacles due to interaction between their boundaries and the swimmers. In this paper, we propose a kinetic-type model to study swimming and directional migration of microscale bimetallic rods in a periodic array of posts with non-circular cross-sections. Both rod position and orientation are taken into account; rod trapping and release on the post boundaries are modeled by empirically characterizing curvature and orientational dependence of the boundary absorption and desorption. Intensity of the directed rod migration, which we call the normalized net flux, is then defined and computed given the geometry of the post array. We numerically study the effect of post spacings on the flux; we also apply shape optimization to find better post shapes that can induce stronger flux. Inspired by preliminary numerical results on two candidate posts, we perform an approximate analysis on a simplified model to show the key geometric features a good post should have. Based on that, three new candidate shapes are proposed which give rise to large fluxes. This approach provides an effective tool and guidance for experimentally designing new devices that induce strong directed migration of microscale swimmers. *

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Bimetallic Microswimmers Speed Up in Confining Channels

Cited by 90 publications

References 63 publications

Metachronal Swimming with Rigid Arms near Boundaries

Metachronal Swimming with Rigid Arms near Boundaries

Shape-dependent guidance of active Janus particles by chemically patterned surfaces

Directed Migration of Microscale Swimmers by an Array of Shaped Obstacles: Modeling and Shape Optimization

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