A general flux-based analysis for spherical electrocatalytic nanomotors

Nourhani, Amir; Lammert, Paul E.; Crespi, Vincent H.; Borhan, Ali

doi:10.1063/1.4904951

Cited by 33 publications

(39 citation statements)

References 82 publications

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“…The half‐cathodic reaction occurs on the Au surface where the hydrogen ions are consumed. (Equation ) The production of hydrogen ion on the TiO 2 surface and its consumption on the Au surface lead to an asymmetric distribution of ions around the microbowl, which drives the micromotor to undergo self‐phoretic propulsion toward the TiO 2 side.…”

Section: Resultsmentioning

confidence: 99%

Structure‐Dependent Optical Modulation of Propulsion and Collective Behavior of Acoustic/Light‐Driven Hybrid Microbowls

Tang

Zhang

Zhao

et al. 2019

Adv Funct Materials

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120

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Hybrid light/acoustic-powered microbowl motors, composed of gold (Au) and titanium dioxide (TiO 2 ) with a structure-dependent optical modulation of both their movement and collective behavior are reported by reversing the inner and outer positions of Au and TiO 2 . The microbowl propels in an acoustic field toward its exterior side. UV light activates the photochemical reaction on the TiO 2 surface in the presence of hydrogen peroxide and the Au/TiO 2 system moves toward its TiO 2 side by self-electrophoresis. Controlling the light intensity allows switching of the dominant propulsion mode and provides braking or reversal of motion direction when TiO 2 is on the interior, or accelerated motion when the TiO 2 is on its exterior. Theoretical simulations offer an understanding of the acoustic streaming flow and self-electrophoretic fluid flow induced by the asymmetric distribution of ions around the microbowl. The light-modulation behavior along with the tunable structure also leads to the control of the swarm behaviors under the acoustic field, including expansion or compaction of ensembles of microbowls with interior and exterior TiO 2 , respectively. Such structure-dependent motion control thus paves the way for a variety of complex microscale operations, ranging from cargo transport to drug delivery in biomedical and environmental applications.

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Section: Resultsmentioning

confidence: 99%

Structure‐Dependent Optical Modulation of Propulsion and Collective Behavior of Acoustic/Light‐Driven Hybrid Microbowls

Tang

Zhang

Zhao

et al. 2019

Adv Funct Materials

Self Cite

120

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“…The products can also phase separate to form bubbles which apply a propulsive thrust. Experimental and continuum theoretical studies of these propulsion mechanisms have been undertaken for locomotors in unbounded media, including for the mechanism of self-neutral diffusiophoresis [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56], for ionic diffusiophoresis [57][58][59][60][61][62][63][64], auto-electrophoresis [34,[65][66][67][68][69][70] and for bubble propulsion [71][72][73]. See also the review by Balazs et al [74] for molecular dynamics perspectives on calculating the diffusiophoretic propulsion.…”

Section: Introductionmentioning

confidence: 99%

Self-propelled colloidal particle near a planar wall: A Brownian dynamics study

et al. 2018

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Miniaturized, self-propelled locomotors use chemo-mechanical transduction mechanisms to convert fuel in the environment to autonomous motion. Recent experimental and theoretical studies demonstrate that these autonomous engines can passively follow the contours of solid boundaries they encounter. Boundary guidance, however, is not necessarily stable: Mechanical disturbances can cause the motor to hydrodynamically depart from the passively guided pathway. Furthermore, given the scaled-down size of micromotors (typically 100 nm -10 µm), Brownian thermal fluctuation forces are necessarily important and these stochastic forces can randomize passively-steered trajectories.Here we examine theoretically the stability of boundary guided motion of micromotors along infinite planar walls to mechanical disturbances and to Brownian forces. Our aim is to understand under what conditions this passively guided motion is stable. We choose a locomotor design in which spherical colloids are partially coated with a catalytic cap that reacts with solute to produce a product. The product is repelled from the particle surface, causing the particle to move with the inert face at the front (autonomous motion via self-diffusiophoresis). When propelled towards a planar wall, deterministic hydrodynamic studies demonstrate that these locomotors can exhibit, for large enough cap sizes, steady trajectories in which the particle either skims unidirectionally along the surface at a constant distance from the wall, or becomes stationary. We first investigate the linear hydrodynamic stability of these states by expanding the equations of motion about the states, and find that linear perturbations decay exponentially in time. We then study the effects of thermal fluctuations by formulating a Langevin equation for the particle motion which includes the Brownian stochastic force. The Pećlet number scales the ratio of deterministic to Brownian forces, where Pe = πµa 2ṽ c /k B T and a denotes the colloid radius, µ the continuous phase viscosity,ṽ c the characteristic diffusiophoretic velocity and k B T the thermal energy. The skimming and stationary states are found to persist for Pe above 10 3 . At Pe below 200, the trajectory of a locomotor approaching the wall is unpredictable. We present representative individual trajectories along with probability distributions for statistical ensembles of particles, quantifying the effects of thermal fluctuations and illustrating the transition from unpredictable to passively guided motion. *

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“…In recent years, significant advances have been made in actuating microstructures by hydrodynamic force, 19 laser manipulation, 20,21 bacterial motion, 22–24 magnetic force, 6,14 chemical propulsion, 25,26 and acoustic waves. 27–29 Yue et al fabricated laser-actuated microgears with rotation rates around 60 revolutions per minute (RPM) at 2 watts.…”

Section: Introductionmentioning

confidence: 99%

Acoustofluidic actuation of in situ fabricated microrotors

et al. 2016

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We have demonstrated in situ fabricated and acoustically actuated microrotors. A polymeric microrotor with predefined oscillating sharp-edge structures is fabricated in situ by applying a patterned UV light to polymerize a photocrosslinkable polyethylene glycol solution inside a microchannel around a polydimethylsiloxane axle. To actuate the microrotors by oscillating the sharp-edge structures, we employed piezoelectric transducers which generate tunable acoustic waves. The resulting acoustic streaming flows rotate the microrotors. The rotation rate is tuned by controlling the peak-to-peak voltage applied to the transducer. A 6-arm microrotor can exceed 1200 revolutions per minute. Our technique is an integration of single-step microfabrication, instant assembly around the axle, and easy acoustic actuation for various applications in microfluidics and microelectromechanical systems (MEMS).

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A general flux-based analysis for spherical electrocatalytic nanomotors

Cited by 33 publications

References 82 publications

Structure‐Dependent Optical Modulation of Propulsion and Collective Behavior of Acoustic/Light‐Driven Hybrid Microbowls

Structure‐Dependent Optical Modulation of Propulsion and Collective Behavior of Acoustic/Light‐Driven Hybrid Microbowls

Self-propelled colloidal particle near a planar wall: A Brownian dynamics study

Acoustofluidic actuation of in situ fabricated microrotors

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