Diffusiophoretic Self-Propulsion for Partially Catalytic Spherical Colloids

Graaf, Joost de; Rempfer, Georg; Holm, Christian

doi:10.1109/tnb.2015.2403255

Cited by 36 publications

(57 citation statements)

References 74 publications

(192 reference statements)

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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%

“…This homogeneity allows one to consider only the first Legendre mode of the solute flux to obtain the swimming speed. The propulsion speed of a self-diffusiophoretic particle is given by [45] …”

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%

“…These last two parameters are choices that enable us to compute the speed in the simulation and are based on the values in Ref. [45], but otherwise do not affect our results for the swimming efficiency.…”

Section: Finite Element Simulationsmentioning

confidence: 99%

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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: Discussion and Outlookmentioning

confidence: 99%

Section: Finite Element Simulationsmentioning

confidence: 99%

Section: Finite Element Simulationsmentioning

confidence: 99%

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

Kreissl

Holm

Graaf

2016

The Journal of Chemical Physics

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“…self-diffusiophoresis [3,[14][15][16][17][18], self-induced electrophoretic flow, [19,20] and selfthermophoresis [4,21]. In many realizations, the particle motion is attributed to a microscopically thin boundary layer adjacent to the solid-fluid interface, which interacts with a self-generated field, such as electrical potential, solute concentration and temperature.…”

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confidence: 99%

Self-Propulsion Mechanism of Active Janus Particles in Near-Critical Binary Mixtures

Samin

Roij

2015

Phys. Rev. Lett.

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Gold-capped Janus particles immersed in a near-critical binary mixture can be propelled using illumination. We employ a non-isothermal diffuse interface approach to investigate the self-propulsion mechanism of a single colloid. We attribute the motion to body forces at the edges of a micronsized droplet that nucleates around the particle. Thus, the often-used concept of a surface velocity cannot account for the self-propulsion. The particle's swimming velocity is related to the droplet shape and size, which is determined by a so-called critical isotherm. Two distinct swimming regimes exist, depending on whether the droplet partially or completely covers the particle. Interestingly, the dependence of the swimming velocity on temperature is non-monotonic in both regimes.The study of self-propelling synthetic colloids is an area of intense active research [1,2]. The out-of-equilibrium directed motion of these colloidal microswimmers is maintained by a constant energy input which originates from their own activity. The directed swimming, coupled to the particle's rotational diffusion, leads to a significant increase in the effective diffusion coefficient [3][4][5] and to complex collective behavior, such as dynamical phaseseparation [6][7][8] and clustering [9][10][11]. Optimization of the microswimmers design is essential for realizing applications such as targeted cargo and drug delivery, parallel assembly and scavenging of contaminants [1,12,13].The design of synthetic swimmers requires an understanding of the underlying mechanisms for the self-propulsion, e.g.self-diffusiophoresis [3, 14-18], self-induced electrophoretic flow, [19,20] and selfthermophoresis [4,21]. In many realizations, the particle motion is attributed to a microscopically thin boundary layer adjacent to the solid-fluid interface, which interacts with a self-generated field, such as electrical potential, solute concentration and temperature. Body forces within this layer give rise to an apparent slip velocity at the surface [22] while the fluid outside the interfacial layer is considered force-free. Thus, the particle motion is completely determined by the slip velocity distribution on its surface [17,23]. However, this simple picture breaks down when the self-generated field extends to a region with a size similar to that of the particle. In this Letter we explore such a scenario of self-diffusiophoresis due to a local solvent demixing, leading to a complex swimming behavior arising from the coupling of the self-generated chemical potential gradients and the fluid motion.We focus on a recently realized new class of swimmer consisting of Janus colloids immersed in a near-critical binary mixture. Local heating of the colloid surface and the ensuing solvent demixing propels these particles, which exhibit fascinating individual and collective behaviour [5,6,[24][25][26]. A similar system was studied by Araki and Fukai [27] but in their simulations heating is periodically applied to the whole mixture. In this work we study the self-propulsion mec...

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Nanoparticle Translocation through Conical Nanopores: A Finite Element Study of Electrokinetic Transport

Rempfer

Ehrhardt

Holm

et al. 2016

Macro Theory & Simulations

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Recent years have seen a surge of interest in nanopores because such structures show a strong potential for characterizing macromolecules, e.g., DNA. Here, the authors theoretically investigate the translocation of a spherical nanoparticle through a conical nanocapillary, by numerically solving the coupled system of electrokinetic continuum equations. Based on their findings, the authors formulate simple guidelines for obtaining the maximum current signal during the translocation event, which should be transferable to other nanopore geometries. In addition, the dependence of the signal strength on particle properties, such as surface charge and size, is evaluated. Finally, the authors identify conditions under which the translocation is prevented by the formation of a strong electroosmotic barrier and show that the particle may even become trapped at the pore orifice, without imposing an external hydrostatic pressure difference.

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Diffusiophoretic Self-Propulsion for Partially Catalytic Spherical Colloids

Cited by 36 publications

References 74 publications

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

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

Self-Propulsion Mechanism of Active Janus Particles in Near-Critical Binary Mixtures

Nanoparticle Translocation through Conical Nanopores: A Finite Element Study of Electrokinetic Transport

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