Chemical micromotors self-assemble and self-propel by spontaneous symmetry breaking

Yu, Tingting; Chuphal, Prabha; Thakur, Snigdha; Reigh, Shang Yik; Singh, Dhruv; Fischer, Peer

doi:10.1039/c8cc06467a

Cited by 53 publications

(55 citation statements)

References 27 publications

(43 reference statements)

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“…This feature may be used to aid in the understanding of the collective behavior of many-sphere systems, and to provide a route to the construction of complex self-assembled structures in the laboratory. [25][26][27] The two-sphere dynamics studied in this paper may be regarded as an elementary process that contributes to the collective dynamics of mixtures of active and passive particles [28][29][30] and sphere dimers with non-rigid bonds. The study provides insight into the mechanisms that could lead to dynamic clusters of various types that not only move but may also fragment and reassemble.…”

Section: Resultsmentioning

confidence: 99%

“…[25][26][27] In this connection, recent experimental and computational studies have considered mixtures of chemically active and inactive spherical particles that exhibit interesting self-assembly and emergent dynamics. [28][29][30] As in the present study, the dynamics of such mixtures will depend on both hydrodynamic and chemical, temperature, or electric fields that exist in the system. 21,22,[31][32][33][34][35] In Section 2 we present continuum solutions for the reactiondiffusion and Stokes equations for this problem, and Section 3 describes the particle-based simulation method.…”

Section: Introductionmentioning

confidence: 80%

“…However, in many experiments, the active particles have micrometer or nanometer dimensions and for such systems thermal fluctuations should be taken into account. 23,[25][26][27]29,30 In addition, as one moves to small nanometer 23 or even Angstrom 12 scales the assumptions of continuum dynamics may no longer apply. The coarse-grain particle-based simulations do not make such assumptions.…”

Section: Microscopic Dynamicsmentioning

confidence: 99%

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Diffusiophoretically induced interactions between chemically active and inert particles

et al. 2018

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In the presence of a chemically active particle, a nearby chemically inert particle can respond to a concentration gradient and move by diffusiophoresis. The nature of the motion is studied for two cases: first, a fixed reactive sphere and a moving inert sphere, and second, freely moving reactive and inert spheres. The continuum reaction-diffusion and Stokes equations are solved analytically for these systems and microscopic simulations of the dynamics are carried out. Although the relative velocities of the spheres are very similar in the two systems, the local and global structures of streamlines and the flow velocity fields are found to be quite different. For freely moving spheres, when the two spheres approach each other the flow generated by the inert sphere through diffusiophoresis drags the reactive sphere towards it. This leads to a self-assembled dimer motor that is able to propel itself in solution. The fluid flow field at the moment of dimer formation changes direction. The ratio of sphere sizes in the dimer influences the characteristics of the flow fields, and this feature suggests that active self-assembly of spherical colloidal particles may be manipulated by sphere-size changes in such reactive systems.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 80%

Section: Microscopic Dynamicsmentioning

confidence: 99%

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Diffusiophoretically induced interactions between chemically active and inert particles

et al. 2018

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“…However, they can also lead to phase separation into static macroscopic phases with welldefined stoichiometry, not unlike equilibrium phase separation, as was found in our recent work [4], in which we explored phase separation in mixtures of chemically active particles interacting through long-ranged unscreened chemical fields. Experimentally, such nonreciprocal interactions have recently been observed in a variety of systems composed of isotropic active colloids [24][25][26].…”

Section: Introductionmentioning

confidence: 98%

Scalar Active Mixtures: The Nonreciprocal Cahn-Hilliard Model

2020

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Pair interactions between active particles need not follow Newton's third law. In this work, we propose a continuum model of pattern formation due to nonreciprocal interaction between multiple species of scalar active matter. The classical Cahn-Hilliard model is minimally modified by supplementing the equilibrium Ginzburg-Landau dynamics with particle-number-conserving currents, which cannot be derived from a free energy, reflecting the microscopic departure from action-reaction symmetry. The strength of the asymmetry in the interaction determines whether the steady state exhibits a macroscopic phase separation or a traveling density wave displaying global polar order. The latter structure, which is equivalent to an active selfpropelled smectic phase, coarsens via annihilation of defects, whereas the former structure undergoes Ostwald ripening. The emergence of traveling density waves, which is a clear signature of broken timereversal symmetry in this active system, is a generic feature of any multicomponent mixture with microscopic nonreciprocal interactions.

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“…Active particles can be made from a variety of materials, including metals, polystyrene, silica, polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS), and hydrogels (5,(7)(8)(9), and in many different shapes, such as spheres (13), rods (8,9), and gears (10). Examples of active particles include molecular motors (14,15), microorganisms (8), self-propelling (13) and self-rotating colloids (10), and particles propelled via symmetry breaking (16,17). Propulsion speeds ranging from microns to tens of millimeters per second have been demonstrated (8).…”

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confidence: 99%

Scale-free, programmable design of morphable chain loops of kilobots and colloidal motors

Agrawal

Glotzer

2020

Proc. Natl. Acad. Sci. U.S.A.

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Micron-scale robots require systems that can morph into arbitrary target configurations controlled by external agents such as heat, light, electricity, and chemical environment. Achieving this behavior using conventional approaches is challenging because the available materials at these scales are not programmable like their macroscopic counterparts. To overcome this challenge, we propose a design strategy to make a robotic machine that is both programmable and compatible with colloidal-scale physics. Our strategy uses motors in the form of active colloidal particles that constantly propel forward. We sequence these motors end-to-end in a closed chain forming a two-dimensional loop that folds under its mechanical constraints. We encode the target loop shape and its motion by regulating six design parameters, each scale-invariant and achievable at the colloidal scale. We demonstrate the plausibility of our design strategy using centimeter-scale robots called kilobots. We use Brownian dynamics simulation to explore the large design space beyond that possible with kilobots, and present an analytical theory to aid the design process. Multiple loops can also be fused together to achieve several complex shapes and robotic behaviors, demonstrated by folding a letter shape “M,” a dynamic gripper, and a dynamic pacman. The material-agnostic, scale-free, and programmable nature of our design enables building a variety of reconfigurable and autonomous robots at both colloidal scales and macroscales.

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Chemical micromotors self-assemble and self-propel by spontaneous symmetry breaking

Abstract: Propelling chemical dimer motors can spontaneously self-assemble from isotropic non-propelling colloids.

Cited by 53 publications

References 27 publications

Diffusiophoretically induced interactions between chemically active and inert particles

Diffusiophoretically induced interactions between chemically active and inert particles

Scalar Active Mixtures: The Nonreciprocal Cahn-Hilliard Model

Scale-free, programmable design of morphable chain loops of kilobots and colloidal motors

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