Steering a thermally activated micromotor with a nearby isothermal wall

Poddar, Antarip; Bandopadhyay, Aditya; Chakraborty, Suman

doi:10.1017/jfm.2021.27

Cited by 8 publications

(30 citation statements)

References 74 publications

(206 reference statements)

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“…2013; Poddar et al. 2021), the effect of heat release from the metallic coating is incorporated through a sudden change of heat flux at the micromotor–solvent interface, given by where denotes the unit normal vector at the micromotor surface. Thus, the following form of the boundary condition holds at the micromotor surface: In this sub-problem, the temperature gradient vanishes at far distances from the particle, i.e.…”

Section: Problem Formulationmentioning

confidence: 99%

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Thermotactic navigation of an artificial microswimmer near a plane wall

Poddar

2023

J. Fluid Mech.

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Despite significant advances in the field of man-made micro- and nanomotors, it remains a challenge to precisely control their motion in bounded environments. Here, we present a theoretical analysis of a thermally activated micromotor near a plane wall under the action of a background linear temperature field. The coupling between the autonomous and field-directed motions has been resolved using a combined analytical–numerical framework comprising general solutions in bispherical coordinates and the reciprocal theorem for creeping flows. Results reveal giant augmentation in swimming speeds, the controlling parameter zones for positive and negative thermotaxes and the flexibility of steering perpendicular to the field gradient for an isolated micromotor. Boundary-instigated thermo-fluidic modulations at different levels of confinements and preferential orientations cause directional switching of both the vertical translation and rotation parallel to the wall, thereby drastically altering the phase portraits of the swimmer dynamics. Contrasting trajectory characteristics, e.g. escape, attraction, are partitioned by unstable separatrices in the phase portraits, while competitive repulsion (attraction) after attraction (repulsion) characteristics emerge for different relative field strengths $\mathcal {S}$ and gradient orientations $\theta _T$ . Below $\mathcal {S}=0.25$ , highly counter-intuitive trajectories result when the micromotor is initially launched from an overlapping escape zone. Moreover, external-field-assisted microswimming can uniquely tune the directionality of wall-parallel translation, broadening the scope of dynamic regulation of self-propulsion. Thus, providing insights into a precisely controlled fuel-free actuation of micromotors near a physical obstacle, the present study stands as a step toward addressing the increasing demand for successful implementation of micromotors in futuristic clinical and environmental applications.

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Section: Problem Formulationmentioning

confidence: 99%

“…This aspect of self-thermophoresis sets it apart from the widely studied self-diffusiophoresis problem, even in an unbounded domain (Poddar et al. 2021). A similar distinction exists between the passive thermophoresis sub-problem (‘’) and a comparable passive diffusiophoresis problem (Vinze et al.…”

Section: Problem Formulationmentioning

confidence: 99%

Thermotactic navigation of an artificial microswimmer near a plane wall

Poddar

2023

J. Fluid Mech.

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“…Similar to the earlier works on force-free microswimming (Lauga & Powers, 2009;Poddar et al, 2020), we decompose the hydrodynamic problem into two sub-problems: (I)-the thrust problem that depicts fluid flow around a fixed microswimmer experiencing only a thermophoretic slip at the surface and (II)-the drag problem dealing with the rigid body motion of a spherical particle where the hydrodynamic drag is only in action. Thus, the force and torque-free conditions can be written as…”

Section: Hydrodynamics Of Near-wall Self-thermophoresismentioning

confidence: 99%

“…The parameters α 1 , α 2 have typical values 200, 100, respectively, so that the swimmer does not approach closer than ∼ 0.01 times the swimmer radius. Such a scenario was previously encountered by others in relation to 'squirmers' (Spagnolie & Lauga, 2012;Li & Ardekani, 2014;Poddar et al, 2020) as well as self-diffusiophoretic microswimmers (Ibrahim & Liverpool, 2016), and different forms of repulsive potentials were employed. It is noteworthy that the squirmer models only deal with the hydrodynamics of the microswimmer, and the wall-induced distortion of the scalar field (e.g.…”

Section: Swimming Trajectoriesmentioning

confidence: 99%

Steering a thermally activated micromotor with a nearby isothermal wall

Poddar,

Bandopadhyay,

Chakraborty

2020

Preprint

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Selective heating of a microparticle surface had been observed to cause its autonomous movement in a fluid medium due to self-generated temperature gradients. In this work, we theoretically investigate the response of such an auto-thermophoretic particle near a planar wall which is held isothermal. We derive an exact solution of the energy equation and employ the Reynolds reciprocal theorem to obtain the translational and rotational swimming velocities in the creeping flow limit. Subsequently, we analyse the trajectories of the micromotor for different thermo-physical and configurational parameters. Results show that the micromotor trajectories can be switched either from wall-bound sliding or stationary state to escape from the near-wall zone by suitably choosing the particle and the surrounding fluid pair having selective thermal conductivity contrasts. Further, we discuss the dependency of this swimming-state transition on the launching orientation and the coverage of the metallic cap. Our results reveal that the scenario addressed here holds several exclusive distinguishing features from the otherwise extensively studied self-diffusiophoresis phenomenon near an inert wall, despite obvious analogies in the respective constitutive laws relating the fluxes with the gradients of the concerned forcing parameters. The most contrasting locomotion behaviour here turns out to be the ability of a self-thermophoretic micromotor to migrate towards the wall with large heated cap even if it is initially directed away from the wall. Besides, during the stationary state of swimming, the cold portion on the micromotor surface faces away from the wall, under all conditions. Such unique aspects of locomotion hold the potential of being harnessed in practice towards achieving intricate control over autonomous motion of microparticles in thermally-regulated fluidic environments.

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“…The special arrangement of two (dimer) or more (chain) touching spherical particles often occurs in many branches of mathematical physics and nanotechnology, such as electrostatic [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ] and optics [ 22 , 23 , 24 , 25 ]. The tangent-sphere coordinate system can be effectively used for analytically tackling some related problems involving particle-wall interactions in various electrokinetic [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ], heat transfer [ 36 , 37 , 38 ], inviscid [ 39 , 40 , 41 , 42 , 43 ], and viscous [ 44 , 45 , 46 , 47 , 48 , 49 , 50 ] flow scenarios. Note that the corresponding tangent-sphere formulation can also be used as the leading-order (‘outer’) near-contact solution of a sphere lying next to an isothermal wall or a planar electrode, both for DC and AC (high-frequency) electrokinetic problems [ 32 , 34 , 36 ].…”

Section: Introductionmentioning

confidence: 99%

Travelling-Wave Electrophoresis, Electro-Hydrodynamics, Electro-Rotation, and Symmetry-Breaking of a Polarizable Dimer in Non-Uniform Fields

Miloh

Avital

2022

Micromachines

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A theoretical framework is presented for calculating the polarization, electro-rotation, travelling-wave dielectrophoresis, electro-hydrodynamics and induced-charge electroosmotic flow fields around a freely suspended conducting dimer (two touching spheres) exposed to non-uniform direct current (DC) or alternating current (AC) electric fields. The analysis is based on employing the classical (linearized) Poisson–Nernst–Planck (PNP) formulation under the standard linearized ‘weak-field’ assumption and using the tangent-sphere coordinate system. Explicit expressions are first derived for the axisymmetric AC electric potential governed by the Robin (mixed) boundary condition applied on the dimer surface depending on the resistance–capacitance circuit (RC) forcing frequency. Dimer electro-rotation due to two orthogonal (out-of-phase) uniform AC fields and the corresponding mobility problem of a polarizable dimer exposed to a travelling-wave electric excitation are also analyzed. We present an explicit solution for the non-linear induced-charge electroosmotic (ICEO) flow problem of a free polarized dimer in terms of the corresponding Stokes stream function determined by the Helmholtz–Smoluchowski velocity slip. Next, we demonstrate how the same framework can be used to obtain an exact solution for the electro-hydrodynamic (EHD) problem of a polarizable sphere lying next to a conducting planar electrode. Finally, we present a new solution for the induced-charge mobility of a Janus dimer composed of two fused spherical colloids, one perfectly conducting and one dielectrically coated. So far, most of the available electrokinetic theoretical studies involving polarizable nano/micro shapes dealt with convex configurations (e.g., spheres, spheroids, ellipsoids) and as such the newly obtained electrostatic AC solution for a dimer provides a useful extension for similar concave colloids and engineered particles.

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Steering a thermally activated micromotor with a nearby isothermal wall

Abstract: Abstract

Cited by 8 publications

References 74 publications

Thermotactic navigation of an artificial microswimmer near a plane wall

Thermotactic navigation of an artificial microswimmer near a plane wall

Steering a thermally activated micromotor with a nearby isothermal wall

Travelling-Wave Electrophoresis, Electro-Hydrodynamics, Electro-Rotation, and Symmetry-Breaking of a Polarizable Dimer in Non-Uniform Fields

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