Electrokinetic effects in catalytic platinum-insulator Janus swimmers

Ebbens, Stephen J.; Gregory, David A.; Dunderdale, Gary J.; Howse, Jonathan R.; Ibrahim, Yahaya; Liverpool, Tanniemola B.; Golestanian, Ramin

doi:10.1209/0295-5075/106/58003

Cited by 218 publications

(334 citation statements)

References 43 publications

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“…Theoretical analysis shows that when the interaction potential Ψ diff decays to zero on a length scale δ a, the force terms in the fluid velocity can be replaced by an effective slip boundary condition, which replaces the condition u| s = 0 [23,38,39,[41][42][43][44][45][46]. The surface slip is given by…”

Section: Discussion and Outlookmentioning

confidence: 99%

“…The swimmer moves due to short-ranged (non-electrostatic) interactions between the oxygen and the swimmer surface, which may be captured within the slip-layer approximation [23,38,39,[41][42][43][44][45][46]. Since oxygen is nowhere consumed on the particle we can choose f J (θ) ≥ 0.…”

Section: Finite Element Simulationsmentioning

confidence: 99%

“…The most common systems that exploit self-phoresis are Au-Pt nanoparticles [25,26,29] and Pt-coated Janus spheres [21-24, 27, 28] that decompose hydrogen peroxide into water and oxygen. The former are considered self-electrophoretic [26,30,31], while for the latter the nature of the phoretic mechanism is still hotly debated [21,23,32].…”

Section: Introductionmentioning

confidence: 99%

“…Only the total surface reaction rate has been established [21]. However, it has been shown that there is a dependence of the reactivity on the thickness of the Pt-coating [23]. The vapourdeposition procedure, by which most Janus particles are created, causes a nonuniform thickness of platinum from the equator to the pole of the Janus swimmer [23].…”

Section: Introductionmentioning

confidence: 99%

“…However, it has been shown that there is a dependence of the reactivity on the thickness of the Pt-coating [23]. The vapourdeposition procedure, by which most Janus particles are created, causes a nonuniform thickness of platinum from the equator to the pole of the Janus swimmer [23]. Therefore, it is likely that there is a heterogeneous reactivity on the particle's surface.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

The efficiency of self-phoretic propulsion mechanisms with surface reaction heterogeneity

Kreissl

Holm

Graaf

2016

The Journal of Chemical Physics

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We consider the efficiency of self-phoretic colloidal particles (swimmers) as a function of the heterogeneity in the surface reaction rate. The set of fluid, species, and electrostatic continuity equations is solved analytically using a linearization and numerically using a finite-element method. To compare spherical swimmers of different size and with heterogeneous catalytic conversion rates, a 'swimmer efficiency' functional η is introduced. It is proven, that in order to obtain maximum swimmer efficiency the reactivity has to be localized at the pole(s). Our results also shed light on the sensitivity of the propulsion speed to details of the surface reactivity, a property that is notoriously hard to measure. This insight can be utilized in the design of new self-phoretic swimmers.

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Section: Discussion and Outlookmentioning

confidence: 99%

Section: Finite Element Simulationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

The efficiency of self-phoretic propulsion mechanisms with surface reaction heterogeneity

Kreissl

Holm

Graaf

2016

The Journal of Chemical Physics

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Photogravitactic Microswimmers

Singh

Uspal

Popescu

et al. 2018

Adv Funct Materials

109

142

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We have studied the dynamics of photo-chemically active colloids made out of silica cores half covered by successive thin layers of Ti and titania, respectively, and moving within aqueous peroxide solutions when exposed to ultraviolet (UV) light. The particles, initially sedimented at the bottom glass wall, exhibit wall-bound states of motion, dependent on the size of the particle, when illuminated from underneath the wall. Upon increasing the intensity of the UV light above a threshold value, which is also dependent on the size of the particle, the particles lift off the wall and move way from it, i.e., they exhibit a photo-gravitactic behavior bearing similarities with that of microorganisms such as phytoplankton and zooplankton. These dependencies on the particle size are rationalized by using a theoretical model of self-phoresis that explicitly accounts for the "shadowing" effect of the Ti/titania layers. This allows us to unequivocally identify the photochemical activity and phototactic response as the key mechanisms beyond the observed phenomenology. Consequently, one has the means to design photo-gravitatic particles that can reversibly switch between operating near a boundary or in the volume away from the boundary by judiciously adjusting the light intensity, i.e., simply by "turning a knob".

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Tadpole‐Shaped Catalytic Janus Microrotors Enabled by Facile and Controllable Growth of Silver Nanotails

Xiao

Zhou

et al. 2020

Adv Funct Materials

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Microrotors are an indispensable component in micromachines, yet their usefulness has been limited by a lack of simple, inexpensive, and controlled fabrication technique that yields microrotors of controlled shapes in large quantities. To address this challenge, the chemical synthesis, characterization, and activation of tadpole-shaped catalytic microrotors that consist of a spherical, platinum (Pt)-coated head and a silver (Ag) nano-tail of tunable lengths are reported herein. Importantly, this tail spontaneously grows on Pt in an aqueous solution of Ag + and hydrogen peroxide (H 2 O 2), at a speed of ≈100 nm s −1 , preferably along the Ag (111) plane. The growth of Ag nanowires is attributed to an electrochemical reaction occurring on a tapered Pt cap, a mechanism corroborated by control experiments with photo-active titania microspheres, which introduce the additional advantage of light-controlled growth. The presence of a long Ag nano-tail on a tadpole-shaped microrotor breaks its symmetry and induces rotation in H 2 O 2 , and its structure-dependent dynamics is quantitatively studied and supported by numerical simulation. The chemical synthesis of microrotors with Ag nano-tails will introduce new designs of micromachines of controlled dynamics, as well as functional materials and devices where mild, controllable, and facile growth of Ag nanostructures is desired.

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Electrokinetic effects in catalytic platinum-insulator Janus swimmers

Cited by 218 publications

References 43 publications

The efficiency of self-phoretic propulsion mechanisms with surface reaction heterogeneity

The efficiency of self-phoretic propulsion mechanisms with surface reaction heterogeneity

Photogravitactic Microswimmers

Tadpole‐Shaped Catalytic Janus Microrotors Enabled by Facile and Controllable Growth of Silver Nanotails

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