Theory of light-activated catalytic Janus particles

Uspal, William E.

doi:10.1063/1.5080967

Cited by 37 publications

(43 citation statements)

References 62 publications

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“…Since TiO 2 is opaque in the ultraviolet (UV), only the surfaces of the photocatalyst that are facing toward the light are activated. This is referred to as shadowing—for a theoretical analysis of light‐activated self‐propelled particles, read W. Uspal, [ 30 ] who considers this effect explicitly. If the catalytic behavior is in any way altered, as expected for when a particle rotates, then we have a likely reason for enhanced activity when

\vec{B} ↑

is applied.…”

Section: Figurementioning

confidence: 99%

Controlling the Speed of Light‐Activated Colloids with a Constant, Uniform Magnetic Field

Landry

Girgis

Gibbs

2020

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It is demonstrated how the strength of activation for photocatalytic, self‐propelled colloids can be enhanced with a constant, uniform magnetic field. When exposed to ultraviolet light and hydrogen peroxide, the titanium dioxide‐based colloids become actively propelled. Due to the iron oxide core, a uniform field oriented perpendicular to the surface where motion takes place causes the asymmetrically shaped particles to rotate, which consequently leads to an increase in activity. The field‐dependent dynamics of self‐propulsion is quantified, and a qualitative description of how this effect arises is proposed. Since the application of the field is easily reversible, modulating the field on‐and‐off serves as a de facto “switch” that controls particle behavior.

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\vec{B} ↑

is applied.…”

Section: Figurementioning

confidence: 99%

Controlling the Speed of Light‐Activated Colloids with a Constant, Uniform Magnetic Field

Landry

Girgis

Gibbs

2020

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“…Due to the broken symmetry, one expects the axis to align with an external field gradient [ 30 – 33 ], as experimentally confirmed, e.g., in [ 34 ] for diffusiophoretic Janus particles. The reorientation of microswimmers in external fields is often referred to as taxis and has been studied for various phoretic mechanisms [ 30 , 31 , 33 – 39 ]. Generally, the direction of alignment (parallel or anti-parallel) with respect to an imposed non-homogeneous field gradient is determined by the precise surface properties of the particle and the chosen solvent [ 30 , 40 , 41 ].…”

Section: Introductionmentioning

confidence: 99%

Thermotaxis of Janus particles

et al. 2021

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The interactions of autonomous microswimmers play an important role for the formation of collective states of motile active matter. We study them in detail for the common microswimmer-design of two-faced Janus spheres with hemispheres made from different materials. Their chemical and physical surface properties may be tailored to fine-tune their mutual attractive, repulsive or aligning behavior. To investigate these effects systematically, we monitor the dynamics of a single gold-capped Janus particle in the external temperature field created by an optically heated metal nanoparticle. We quantify the orientation-dependent repulsion and alignment of the Janus particle and explain it in terms of a simple theoretical model for the induced thermoosmotic surface fluxes. The model reveals that the particle’s angular velocity is solely determined by the temperature profile on the equator between the Janus particle’s hemispheres and their phoretic mobility contrast. The distortion of the external temperature field by their heterogeneous heat conductivity is moreover shown to break the apparent symmetry of the problem. Graphic abstract

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“…As active particles function under a sustained energy input within an ambient medium, their effective pair interactions are in general non-reciprocal and can systematically draw both linear and angular momentum from their surroundings. The roles of hydrodynamic flow [18][19][20][21][22][23][24], diffused solute [25][26][27][28][29], local phase change [30] and optical shadowing [31,32] as mediators of these interactions have been studied, as well as guidance by nearby boundaries [33][34][35]. Unravelling the dependence of phoretic and chemotactic effects on the surface profiles of catalyst concentration and solute-colloid interaction [8,[36][37][38] and symmetry-based classifications of pair interactions [39] have opened up the possibility of engineering active colloids with desired behaviour [40,41].…”

Section: Introductionmentioning

confidence: 99%

Pairing, waltzing and scattering of chemotactic active colloids

2019

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We study theoretically an active colloid whose polar axis of self-propulsion rotates to point parallel (antiparallel) to an imposed chemical gradient. We show that the coupling of this 'chemotactic' ('antichemotactic') response to phoretic translational motion yields remarkable two-particle dynamics reflecting the non-central and non-reciprocal character of the interaction. A pair of mutually chemotactic colloids trap each other in a final state of fixed separation resulting in a selfpropelled active dimer. A second type of bound state is observed when the polar axes undergo periodic cycles leading to phase-locked circular motion around a common centre. A pair of swimmers with mismatched phoretic mobilities execute a dance in which they twirl around one another while moving jointly in a wide circle. For sufficiently small initial separation, the speed of self-propulsion controls the transition from bound to scattering states. Mutually anti-chemotactic swimmers always scatter apart. For the special case in which one of the two colloids has uniform surface activity we succeed in exactly classifying the fixed points underlying the bound states, and identify the bifurcations leading to transitions from one type of bound state to another. The varied dynamical behaviours are accessible by tuning the swimmer design and are summarised in state diagrams.

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Theory of light-activated catalytic Janus particles

Cited by 37 publications

References 62 publications

Controlling the Speed of Light‐Activated Colloids with a Constant, Uniform Magnetic Field

Controlling the Speed of Light‐Activated Colloids with a Constant, Uniform Magnetic Field

Thermotaxis of Janus particles

Pairing, waltzing and scattering of chemotactic active colloids

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