Chemically Powered Micro‐ and Nanomotors

Sánchez, Samuel; Soler, Lluís; Katuri, Jaideep

doi:10.1002/anie.201406096

Cited by 862 publications

(711 citation statements)

References 298 publications

(402 reference statements)

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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%

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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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confidence: 99%

“…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].…”

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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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“…These challenges mean that most artificial microrobots actually have no actuators. Rather, they are in most cases rigid monolithic structures, either pushed by chemical reactions 15 or directly manipulated by torques or forces applied by external magnetic fields [16][17][18][19][20] .…”

Section: Introductionmentioning

confidence: 99%

Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots

et al. 2016

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Microorganisms move in challenging environments by periodic changes in body shape. By contrast, current artificial microrobots cannot actively deform, exhibiting at best passive bending under external fields. Here, by taking advantage of the wireless, scalable and spatiotemporally selective capabilities that light allows, we show that soft microrobots consisting of photoactive liquid-crystal elastomers can be driven by structured monochromatic light to perform sophisticated biomimetic motions. We realized continuum yet selectively addressable artificial microswimmers that generate travelling-wave motions to self-propel without external forces or torques, as well as microrobots capable of versatile locomotion behaviours on demand. Both theoretical predictions and experimental results confirm that multiple gaits, mimicking either symplectic or antiplectic metachrony of ciliate protozoa, can be achieved with single microrobots. The principle of using structured light can be extended to other applications that require microscale actuation with sophisticated spatiotemporal coordination for advanced microrobotic technologies. 3Mobile micro-scale robots are envisioned to navigate within the human body to perform minimally invasive diagnostic or therapeutic tasks 1,2 . Biological microorganisms represent the natural inspiration for this vision. For instance, microorganisms successfully swim and move through a variety of fluids and tissues.Locomotion in this regime, where viscous forces dominate over inertia (low Reynolds number), is only possible through non-reciprocal motions demanding spatiotemporal coordination of multiple actuators 3 . A variety of biological propulsion mechanisms at different scales, from the peristalsis of annelids (Fig. 1a) to the metachrony of ciliates (Fig. 1b), are based on the common principle of travelling waves (Fig. 1c). These emerge from the distributed and self-coordinated action of many independent molecular motors 4,5 .Implementing travelling wave propulsion in an artificial device would require many discrete actuators, each individually addressed and powered in a coordinated fashion (Fig. 1d). The integration of actuators into microrobots that are mobile poses additional hurdles, since power and control need to be distributed without affecting the microrobots' mobility. Existing microscale actuators generally rely on applying external magnetic 6-10 , electric 11 , or optical 12,13 fields globally over the entire workspace. However, these approaches do not permit the spatial selectivity required to independently address individual actuators within a micro-device. Nevertheless, complex non-reciprocal motion patterns have been achieved by carefully engineering the response of different regions in a device to a spatially uniform external field 13,14 .The drawback is that this complicates the fabrication process, inhibits down-scaling and constrains the device to a single predefined behaviour. These challenges mean that most artificial microrobots actually have no actuators. Rather...

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“…In recent years there has been a surge of interest in the study of active matter [1,2], in particular concerning self-propelled colloidal particles (swimmers) [3][4][5][6][7]. These systems have been connected to a number of potential applications, including: cancer treatment [8,9], drug delivery [10][11][12][13], soil remediation [14], and microfluidic mixing [15][16][17][18].…”

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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Chemically Powered Micro‐ and Nanomotors

Cited by 862 publications

References 298 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

Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots

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

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