Self-Propelling Nanomotors in the Presence of Strong Brownian Forces

Lee, Tung‐Chun; Alarcón‐Correa, Mariana; Miksch, Cornelia; Hahn, Klaus-Uwe; Gibbs, John G.; Fischer, Peer

doi:10.1021/nl500068n

Cited by 289 publications

(352 citation statements)

References 35 publications

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“…They are seen as promising candidates for novel techniques in chemical sensing [4] or water treatment [5]. The motion of active colloidal particles has been the subject of numerous experimental [1][2][3]6,7] and theoretical [8][9][10][11][12] studies. One realization is a particle with a catalytic surface promoting a chemical reaction in the surrounding solution [13].…”

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confidence: 99%

Effective Interaction between Active Colloids and Fluid Interfaces Induced by Marangoni Flows

et al. 2016

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We show theoretically that near a fluid-fluid interface a single active colloidal particle generating, e.g., chemicals or a temperature gradient experiences an effective force of hydrodynamic origin. This force is due to the fluid flow driven by Marangoni stresses induced by the activity of the particle; it decays very slowly with the distance from the interface, and can be attractive or repulsive depending on how the activity modifies the surface tension. We show that, for typical systems, this interaction can dominate the dynamics of the particle as compared to Brownian motion, dispersion forces, or self-phoretic effects. In the attractive case, the interaction promotes the self-assembly of particles into a crystal-like monolayer at the interface. DOI: 10.1103/PhysRevLett.116.078301 Significant attention has been paid lately to micrometer sized particles capable of self-induced motility [1][2][3]. They are seen as promising candidates for novel techniques in chemical sensing [4] or water treatment [5]. The motion of active colloidal particles has been the subject of numerous experimental [1][2][3]6,7] and theoretical [8][9][10][11][12] studies. One realization is a particle with a catalytic surface promoting a chemical reaction in the surrounding solution [13]. For an axisymmetric particle lacking fore-and-aft symmetry, the distributions of reactant and product molecules may become nonuniform along its surface and the particle could move due to self-induced phoresis [14]. If the particle is spherically symmetric, it will remain immobile in bulk solution but can be set into motion by the vicinity of walls or other particles (not necessarily active) which break the spherical symmetry [10,[13][14][15][16].A relevant case corresponds to the movement of active particles bounded by a fluid-fluid interface. This situation raises new issues, in particular if the reactants or the products have a significant effect on the properties of the fluid interface implying tensioactivity. For example, it has been recently predicted that catalytically active, spherical particles which are trapped at the interface may be set into motion along the interface by Marangoni flows, selfinduced via the spatially nonuniform distribution of tensioactive molecules [17][18][19]. (A similar motility mechanism can originate from thermally induced Marangoni flows if, e.g., the particle contains a metal cap which is heated by a laser beam [20].) Furthermore, self-induced Marangoni flows, combined with a mechanism of triggering spontaneous symmetry breaking, have also been used to develop self-propelled droplets [21][22][23].However, another category of experimental situations occurs if the particles are not trapped at the interface but may reside in the vicinity of the interface or get near it during their motion. In this study we provide theoretical evidence that such catalytically active or locally heated spherical particles, although immobile in bulk, experience a very strong, long-ranged effective force field due to the Marangoni stresses...

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Effective Interaction between Active Colloids and Fluid Interfaces Induced by Marangoni Flows

et al. 2016

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“…A particular class of active colloids is often connected with these potential applications, namely, artificial selfphoretic colloids [21][22][23][24][25][26][27][28][29]. This is because their fabrication can be well controlled and they appear to be simpler than biological organisms.…”

Section: Introductionmentioning

confidence: 99%

“…These gradients are typically caused by chemical decomposition reactions that take place on the surface of the particle. 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%

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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“…[5][6][7][8][9][10] Several relevant reviews have been published recently. [11][12][13] Circular dichroism (CD) is routinely used to investigate chiral nanomaterials, which absorb and scatter left-and right-circularly polarized light (LCP and RCP) differently depending on the handedness of the nanostructures.…”

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confidence: 99%

Circular Dichroism in Higher‐Order Diffraction Beams from Chiral Quasiplanar Nanostructures

Kuppe

Williams

You

et al. 2018

Advanced Optical Materials

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sensing. [5][6][7][8][9][10] Several relevant reviews have been published recently. [11][12][13] Circular dichroism (CD) is routinely used to investigate chiral nanomaterials, which absorb and scatter left-and right-circularly polarized light (LCP and RCP) differently depending on the handedness of the nanostructures. Such nanostructures can give rise to much stronger CD than chiral molecules, in part because the pitch of the twist is better matched to optical wavelengths. [14][15][16][17][18] In metal nanoparticles, localized surface plasmon resonances (coherent oscillations of the free electrons at the surface) can greatly enhance the light-matter interaction and, by extension, the chiroptical interactions. [19][20][21][22] In general, chiroptical interactions can be enhanced by increasing the chirality parameter of the nanostructures [23,24] or of light (optical chirality). [25] Most investigations have been performed on structures with subwavelength dimensions, chiefly because this enables their theoretical treatment within an effective medium approximation. [26] However, diffractive chiral nanomaterials are also of great interest because the CD measured in the diffracted beams can be orders of magnitude larger than that in the zeroth-order beam. [27] Although previous studies have addressed the CD in diffracted beams, those studies were limited to zeroth-and first-order beams. [28][29][30][31][32][33][34] Here, we investigate chiral metal nanostructures that exhibit large CD in the diffracted beams. We show that, for our structures, the third-order diffraction beam gives the strongest CD response. This CD changes sign depending on wavelength. Our results are validated by a good agreement between numerical and experimental data. Moreover, we establish the robustness of our findings by making use of Babinet's principle. In order to identify the origin of the effect, we provide numerical simulations of the near field. These simulations show that for LCP and RCP beams, a difference in the electromagnetic response at the surface can be linked to the far-field CD.The samples measured in this study were fabricated using electron beam lithography (EBL)-a detailed description can be found in the Experimental Section. In Figure 1a, the dimensions and depth profile are schematically shown. The gold U-shaped structures are 1 µm in length, have a separation of 200 nm, and a highly subwavelength thickness. Each square unit cell consists of four U-shaped gold structures rotated by 90° with respect to each other. The dimensions of the actual Miniaturization down to the nanoscale has enabled a new paradigm of ultrathin optical devices, capable of manipulating the direction, polarization, and frequency of light. Great interest is drawn by the promising prospects of deep-subwavelength material dimensions. However, interesting properties and opportunities offered by structures with sizes comparable to the wavelength of light appear to have been overlooked. Here, quasiplanar chiral arrays made of gold are considered and show th...

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Self-Propelling Nanomotors in the Presence of Strong Brownian Forces

Cited by 289 publications

References 35 publications

Effective Interaction between Active Colloids and Fluid Interfaces Induced by Marangoni Flows

Effective Interaction between Active Colloids and Fluid Interfaces Induced by Marangoni Flows

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

Circular Dichroism in Higher‐Order Diffraction Beams from Chiral Quasiplanar Nanostructures

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