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Shrestha A, Olvera de la Cruz M. Enhanced phoretic self-propulsion of active colloids through surface charge asymmetry. Phys Rev E 2024; 109:014613. [PMID: 38366412 DOI: 10.1103/physreve.109.014613] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2023] [Accepted: 12/21/2023] [Indexed: 02/18/2024]
Abstract
Charged colloidal particles propel themselves through asymmetric fluxes of chemically generated ions on their surface. We show that asymmetry in the surface charge distribution provides an additional mode of self-propulsion at the nanoscale for chemically active particles that produce ionic species. Particles of sizes smaller than or comparable to the Debye length achieve directed self-propulsion through surface charge asymmetry even when ionic flux is uniform over its surface. Janus nanoparticles endowed with both surface charge and ionic flux asymmetries result in enhanced propulsion speeds of the order of μm/s or higher. Our work suggests an alternative avenue for specifying surface properties that optimize self-propulsion in ionic media.
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Affiliation(s)
- Ahis Shrestha
- Center for Computation and Theory of Soft Materials, Northwestern University, Evanston, Illinois 60208, USA
- Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, USA
| | - Monica Olvera de la Cruz
- Center for Computation and Theory of Soft Materials, Northwestern University, Evanston, Illinois 60208, USA
- Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, USA
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA
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2
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Wang W. Open Questions of Chemically Powered Nano- and Micromotors. J Am Chem Soc 2023; 145:27185-27197. [PMID: 38063192 DOI: 10.1021/jacs.3c09223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2023]
Abstract
Chemically powered nano- and micromotors are microscopic devices that convert chemical energy into motion. Interest in these motors has grown over the past 20 years because they exhibit interesting collective behaviors and have found potential uses in biomedical and environmental applications. Understanding how these motors operate both individually and collectively and how environments affect their operation is of both fundamental and applied significance. However, there are still significant gaps in our knowledge. This Perspective highlights several open questions regarding the propulsion mechanisms of, interactions among, and impact of confinements on nano- and micromotors driven by self-generated chemical gradients. These questions are based on my own experience as an experimentalist. For each open question, I describe the problem and its significance, analyze the status-quo, identify the bottleneck problem, and propose potential solutions. An underlying theme for these questions is the interplay among reaction kinetics, physicochemical distributions, and fluid flows. Unraveling this interplay requires careful measurements as well as a close collaboration between experimentalists and theoreticians/numerical experts. The interdisciplinary nature of these challenges suggests that their solutions could bring new revelations and opportunities across disciplines such as colloidal sciences, material sciences, soft matter physics, robotics, and beyond.
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Affiliation(s)
- Wei Wang
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong, China, 518055
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3
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Abstract
Active colloids use energy input at the particle level to propel persistent motion and direct dynamic assemblies. We consider three types of colloids animated by chemical reactions, time-varying magnetic fields, and electric currents. For each type, we review the basic propulsion mechanisms at the particle level and discuss their consequences for collective behaviors in particle ensembles. These microscopic systems provide useful experimental models of nonequilibrium many-body physics in which dissipative currents break time-reversal symmetry. Freed from the constraints of thermodynamic equilibrium, active colloids assemble to form materials that move, reconfigure, heal, and adapt. Colloidal machines based on engineered particles and their assemblies provide a basis for mobile robots with increasing levels of autonomy. This review provides a conceptual framework for understanding and applying active colloids to create material systems that mimic the functions of living matter. We highlight opportunities for chemical engineers to contribute to this growing field.
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Affiliation(s)
- Kyle J M Bishop
- Department of Chemical Engineering, Columbia University, New York, NY, USA;
| | - Sibani Lisa Biswal
- Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas, USA
| | - Bhuvnesh Bharti
- Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, Louisiana, USA
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4
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Saud KT, Solomon MJ. Microdynamics of active particles in defect-rich colloidal crystals. J Colloid Interface Sci 2023; 641:950-960. [PMID: 36989821 DOI: 10.1016/j.jcis.2023.03.025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Revised: 02/04/2023] [Accepted: 03/02/2023] [Indexed: 03/11/2023]
Abstract
HYPOTHESIS Because they are self-propulsive, active colloidal particles can interact with their environment in ways that differ from passive, Brownian particles. Here, we explore how interactions in different microstructural regions may contribute to colloidal crystal annealing. EXPERIMENTS We investigate active particles propagating in a quasi-2D colloidal crystal monolayer produced by alternating current electric fields (active-to-passive particle ratio ∼ 1:720). The active particle is a platinum Janus sphere propelled by asymmetric decomposition of hydrogen peroxide. Crystals are characterized for changes in void properties. The mean-squared-displacement of Janus particles are measured to determine how active microdynamics depend on the local microstructure, which is comprised of void regions, void-adjacent regions (defined as within three particle diameters of a void), and interstitial regions. FINDINGS At active particle energy EA = 2.55 kBT, the average void size increases as much as three times and the average void anisotropy increases about 40% relative to the passive case. The average microdynamical enhancement, <δ(t)>, of Janus particles in the crystal relative to an equivalent passive Janus particle is reduced compared to that of a free, active particle (<δ(t) > is 1.88 ± 0.04 and 2.66 ± 0.08, respectively). The concentration of active particles is enriched in void and void-adjacent regions. Active particles exhibit the greatest change in dynamics relative to the passive control in void-adjacent regions (<δ(t)> = 2.58 ± 0.06). The results support the conjecture that active particle microdynamical enhancement in crystal lattices is affected by local defect structure.
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Affiliation(s)
- Keara T Saud
- Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, United States; Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States
| | - Michael J Solomon
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States; Department of Chemical Engineering, University of Michigan, Ann Arbor, MI, United States.
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5
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Wang L, Simmchen J. Determination of the swimming mechanism of Au@TiO 2 active matter and implications on active-passive interactions. SOFT MATTER 2023; 19:540-549. [PMID: 36541522 DOI: 10.1039/d2sm01097f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Non-equilibrium dynamic assembly attracts considerable attention due to the possibility of forming diverse structures that can potentially lead to functional materials. Despite significant progress in understanding and modelling, the complexity of the system implies that different phases of the assembly formation are governed by different interactions. It is clear that both, hydrodynamic and chemical interactions stem from the activity of the particle, but correlation to specific chemical species remains not yet understood. Here, we investigate the origin of the main driving forces for light-driven Au@TiO2 micromotors and look at the implication this causes for the interactions between active and passive particles. We develop precision experimental measurements of the photochemical reaction rate, which are correlated with the observed speed of Au@TiO2 micromotors. The comparison with two distinct models allows the conclusion that the dominant propulsion mechanism of the active particles is self-electrophoresis based on the self-generated H+ gradient. We verify this assumption by adding salt and confirm the dependence of the expected swimming behaviour on salt concentration and investigate the consequences for raft formation in COMSOL simulations.
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Affiliation(s)
- Linlin Wang
- Department of Physical Chemistry, TU Dresden, Zellescher Weg 19, 01069 Dresden, Germany.
| | - Juliane Simmchen
- Department of Physical Chemistry, TU Dresden, Zellescher Weg 19, 01069 Dresden, Germany.
- Pure and Applied Chemistry, University of Strathclyde, Glasgow, UK.
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6
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Zhou X, Lei L, Zeng Y, Lu X, Liang F, Zhang L, Lin G. High salinity effects on the depletion attraction in colloid-polymer mixtures. J Colloid Interface Sci 2022; 631:155-164. [DOI: 10.1016/j.jcis.2022.10.164] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2022] [Revised: 10/28/2022] [Accepted: 10/31/2022] [Indexed: 11/06/2022]
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7
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Lei L, Cheng R, Zhou Y, Yang T, Liang B, Wang S, Zhang X, Lin G, Zhou X. Estimating the velocity of chemically-driven Janus colloids considering the anisotropic concentration field. Front Chem 2022; 10:973961. [PMID: 36034655 PMCID: PMC9411653 DOI: 10.3389/fchem.2022.973961] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Accepted: 07/13/2022] [Indexed: 11/30/2022] Open
Abstract
The application of the active colloids is strongly related to their self-propulsion velocity, which is controlled by the generated anisotropic concentration field. We investigated the effect of this anisotropy on velocity induced by numerical treatments and size of Janus colloids. The far-field approximation is effective in estimating the velocity, even though it neglects the shape effect on the anisotropy of the concentration field. If the surface mobility contrast between the active and the inert part is moderate, the spherical approximation is feasible for sphere-like Janus colloids. Legendre expansion of the concentration field causes artificial anisotropy. Raising the order of the expansion can suppress this effect, but also distorts the concentration field at the top of active part. Thus, the order of the expansion should be chosen carefully depending on the goal of the study. Based on the verified Legendre expansion method and ionic-diffusiophoresis model, we show that due to the size-effect on both the concentration field and the surface mobility, increasing size of colloids can lower the self-propulsion velocity. Our finding is consistent with previous experimental observations without fitting parameter, shedding new light on the self-propulsion mechanism of chemically-driven active colloids. We further show a velocity reversal at high overall ζ potential induced by increasing size, providing a new way for controlling the dynamics of acitve colloids.
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Affiliation(s)
- Lijie Lei
- College of Aviation Engineering, Civil Aviation Flight University of China, Guanghan, China
| | - Rong Cheng
- School of Mechanical and Electrical Engineering, Guangxi Science and Technology Normal University, Laibin, China
| | - Yuxiu Zhou
- School of Mechanical and Electrical Engineering, Guangxi Science and Technology Normal University, Laibin, China
| | - Tiezhu Yang
- School of Mechanical and Electrical Engineering, Guangxi Science and Technology Normal University, Laibin, China
| | - Beirong Liang
- School of Mechanical and Electrical Engineering, Guangxi Science and Technology Normal University, Laibin, China
| | - Shuo Wang
- Julong College, Shenzhen Technology University, Shenzhen, China
| | - Xinyuan Zhang
- Institute for Advanced Study, Shenzhen University, Shenzhen, China
| | - Guanhua Lin
- Institute for Advanced Study, Shenzhen University, Shenzhen, China
| | - Xuemao Zhou
- School of Mechanical and Electrical Engineering, Guangxi Science and Technology Normal University, Laibin, China
- *Correspondence: Xuemao Zhou,
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8
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Domínguez A, Popescu MN. A fresh view on phoresis and self-phoresis. Curr Opin Colloid Interface Sci 2022. [DOI: 10.1016/j.cocis.2022.101610] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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9
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Heckel S, Bilsing C, Wittmann M, Gemming T, Büttner L, Czarske J, Simmchen J. Beyond Janus Geometry: Characterization of Flow Fields around Nonspherical Photocatalytic Microswimmers. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2022; 9:e2105009. [PMID: 35839469 PMCID: PMC9403636 DOI: 10.1002/advs.202105009] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Revised: 05/04/2022] [Indexed: 05/25/2023]
Abstract
Catalytic microswimmers that move by a phoretic mechanism in response to a self-induced chemical gradient are often obtained by the design of spherical janus microparticles, which suffer from multi-step fabrication and low yields. Approaches that circumvent laborious multi-step fabrication include the exploitation of the possibility of nonuniform catalytic activity along the surface of irregular particle shapes, local excitation or intrinsic asymmetry. Unfortunately, the effects on the generation of motion remain poorly understood. In this work, single crystalline BiVO4 microswimmers are presented that rely on a strict inherent asymmetry of charge-carrier distribution under illumination. The origin of the asymmetrical flow pattern is elucidated because of the high spatial resolution of measured flow fields around pinned BiVO4 colloids. As a result the flow from oxidative to reductive particle sides is confirmed. Distribution of oxidation and reduction reactions suggests a dominant self-electrophoretic motion mechanism with a source quadrupole as the origin of the induced flows. It is shown that the symmetry of the flow fields is broken by self-shadowing of the particles and synthetic surface defects that impact the photocatalytic activity of the microswimmers. The results demonstrate the complexity of symmetry breaking in nonspherical microswimmers and emphasize the role of self-shadowing for photocatalytic microswimmers. The findings are leading the way toward understanding of propulsion mechanisms of phoretic colloids of various shapes.
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Affiliation(s)
- Sandra Heckel
- TU DresdenChair of Physical ChemistryZellescher Weg 1901069DresdenGermany
| | - Clemens Bilsing
- TU DresdenLaboratory for Measurement and Sensor System TechniqueHelmholtzstraße 1801069DresdenGermany
| | - Martin Wittmann
- TU DresdenChair of Physical ChemistryZellescher Weg 1901069DresdenGermany
| | - Thomas Gemming
- Leibniz Institute for Solid State and Materials Research DresdenHelmholtzstraße 2001069DresdenGermany
| | - Lars Büttner
- TU DresdenLaboratory for Measurement and Sensor System TechniqueHelmholtzstraße 1801069DresdenGermany
- Competence Center Biomedical Computational Laser Systms (BIOLAS)Helmholtzstraße 1801069DresdenGermany
| | - Jürgen Czarske
- TU DresdenLaboratory for Measurement and Sensor System TechniqueHelmholtzstraße 1801069DresdenGermany
- Competence Center Biomedical Computational Laser Systms (BIOLAS)Helmholtzstraße 1801069DresdenGermany
| | - Juliane Simmchen
- TU DresdenChair of Physical ChemistryZellescher Weg 1901069DresdenGermany
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10
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Chen X, Xu Y, Zhou C, Lou K, Peng Y, Zhang HP, Wang W. Unraveling the physiochemical nature of colloidal motion waves among silver colloids. SCIENCE ADVANCES 2022; 8:eabn9130. [PMID: 35613263 PMCID: PMC9132452 DOI: 10.1126/sciadv.abn9130] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Traveling waves are common in biological and synthetic systems, including the recent discovery that silver (Ag) colloids form traveling motion waves in H2O2 and under light. Here, we show that this colloidal motion wave is a heterogeneous excitable system. The Ag colloids generate traveling chemical waves via reaction-diffusion, and either self-propel through self-diffusiophoresis ("ballistic waves") or are advected by diffusio-osmotic flows from gradients of neutral molecules ("swarming waves"). Key results include the experimental observation of traveling waves of OH- with pH-sensitive fluorescent dyes and a Rogers-McCulloch model that qualitatively and quantitatively reproduces the key features of colloidal waves. These results are a step forward in elucidating the Ag-H2O2-light oscillatory system at individual and collective levels. In addition, they pave the way for using colloidal waves either as a platform for studying nonlinear phenomena, or as a tool for colloidal transport and for information transmission in microrobot ensembles.
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Affiliation(s)
- Xi Chen
- Sauvage Laboratory for Smart Materials, School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, China
| | - Yankai Xu
- School of Physics and Astronomy and Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Chao Zhou
- Sauvage Laboratory for Smart Materials, School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, China
| | - Kai Lou
- Guangzhou Kayja-Optics Technology Co. Ltd., Guangzhou 511458, China
| | - Yixin Peng
- Sauvage Laboratory for Smart Materials, School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, China
| | - H. P. Zhang
- School of Physics and Astronomy and Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240, China
- Corresponding author. (W.W.); (H.P.Z.)
| | - Wei Wang
- Sauvage Laboratory for Smart Materials, School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, China
- Corresponding author. (W.W.); (H.P.Z.)
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11
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Ryabov A, Tasinkevych M. Enhanced diffusivity in microscopically reversible active matter. SOFT MATTER 2022; 18:3234-3240. [PMID: 35388861 DOI: 10.1039/d2sm00054g] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The physics of self-propelled objects at the nanoscale is a rapidly developing research field where recent experiments have focused on the motion of individual catalytic enzymes. Contrary to the experimental advancements, theoretical understanding of the possible self-propulsion mechanisms at these scales is limited. A particularly puzzling question concerns the origins of the reportedly high diffusivities of the individual enzymes. Here we start with the fundamental principle of microscopic reversibility (MR) of chemical reactions powering self-propulsion and demonstrate that MR can lead to an increase of the particle mobility and of the short- and long-time diffusion coefficients as compared to dynamics where MR is neglected. Furthermore, the derived diffusion coefficients are enhanced due to the action of an external force. These results can shed new light on interpretations of the measured diffusivities and help to test the relevance of MR for the active motion of individual nanoswimmers.
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Affiliation(s)
- Artem Ryabov
- Charles University, Faculty of Mathematics and Physics, Department of Macromolecular Physics, V Holešovičkách 2, 180 00 Praha 8, Czech Republic.
- Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
- Centro de Física Teórica e Computacional, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
| | - Mykola Tasinkevych
- Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
- Centro de Física Teórica e Computacional, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
- SOFT Group, School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, UK.
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12
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Sharan P, Xiao Z, Mancuso V, Uspal WE, Simmchen J. Upstream Rheotaxis of Catalytic Janus Spheres. ACS NANO 2022; 16:4599-4608. [PMID: 35230094 DOI: 10.1021/acsnano.1c11204] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Fluid flow is ubiquitous in many environments that form habitats for microorganisms. Therefore, it is not surprising that both biological and artificial microswimmers show responses to flows that are determined by the interplay of chemical and physical factors. In particular, to deepen the understanding of how different systems respond to flows, it is crucial to comprehend the influence played by swimming pattern. The tendency of organisms to navigate up or down the flow is termed rheotaxis. Early theoretical studies predicted a positive rheotactic response for puller-type spherical Janus micromotors. However, recent experimental studies have focused on pusher-type Janus particles, finding that they exhibit cross-stream migration in externally applied flows. To study the response to the flow of swimmers with a qualitatively different flow pattern, we introduce Cu@SiO2 micromotors that swim toward their catalytic cap. On the basis of experimental observations, and supported by flow field calculations using a model for self-electrophoresis, we hypothesize that they behave effectively as a puller-type system. We investigate the effect of externally imposed flow on these spherically symmetrical Cu@SiO2 active Janus colloids, and we indeed observe a steady upstream directional response. Through a simple squirmer model for a puller, we recover the major experimental observations. Additionally, the model predicts a "jumping" behavior for puller-type micromotors at high flow speeds. Performing additional experiments at high flow speeds, we capture this phenomenon, in which the particles "roll" with their swimming axes aligned to the shear plane, in addition to being dragged downstream by the fluid flow.
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Affiliation(s)
- Priyanka Sharan
- Physical Chemistry, TU Dresden, Zellescher Weg 19, Dresden 01069, Germany
| | - Zuyao Xiao
- Physical Chemistry, TU Dresden, Zellescher Weg 19, Dresden 01069, Germany
| | - Viviana Mancuso
- Department of Mechanical Engineering, University of Hawai'i at Ma̅noa, Honolulu 96822, Hawaii, United States
| | - William E Uspal
- Department of Mechanical Engineering, University of Hawai'i at Ma̅noa, Honolulu 96822, Hawaii, United States
| | - Juliane Simmchen
- Physical Chemistry, TU Dresden, Zellescher Weg 19, Dresden 01069, Germany
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13
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Peng Y, Xu P, Duan S, Liu J, Moran JL, Wang W. Generic Rules for Distinguishing Autophoretic Colloidal Motors. Angew Chem Int Ed Engl 2022; 61:e202116041. [PMID: 34994039 DOI: 10.1002/anie.202116041] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Indexed: 12/28/2022]
Abstract
Distinguishing the operating mechanisms of nano- and micromotors powered by chemical gradients, i.e. "autophoresis", holds the key for fundamental and applied reasons. In this article, we propose and experimentally confirm that the speeds of a self-diffusiophoretic colloidal motor scale inversely to its population density but not for self-electrophoretic motors, because the former is an ion source and thus increases the solution ionic strength over time while the latter does not. They also form clusters in visually distinguishable and quantifiable ways. This pair of rules is simple, powerful, and insensitive to the specific material composition, shape or size of a colloidal motor, and does not require any measurement beyond typical microscopy. These rules are not only useful in clarifying the operating mechanisms of typical autophoretic micromotors, but also in predicting the dynamics of unconventional ones that are yet to be experimentally realized, even those involving enzymes.
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Affiliation(s)
- Yixin Peng
- Sauvage Laboratory for Smart Materials, School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong, 518055, China
| | - Pengzhao Xu
- Sauvage Laboratory for Smart Materials, School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong, 518055, China
| | - Shifang Duan
- Sauvage Laboratory for Smart Materials, School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong, 518055, China
| | - Jiayu Liu
- Sauvage Laboratory for Smart Materials, School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong, 518055, China
| | | | - Wei Wang
- Sauvage Laboratory for Smart Materials, School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong, 518055, China
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14
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15
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Liebchen B, Mukhopadhyay AK. Interactions in active colloids. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 34:083002. [PMID: 34788232 DOI: 10.1088/1361-648x/ac3a86] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Accepted: 11/16/2021] [Indexed: 06/13/2023]
Abstract
The past two decades have seen a remarkable progress in the development of synthetic colloidal agents which are capable of creating directed motion in an unbiased environment at the microscale. These self-propelling particles are often praised for their enormous potential to self-organize into dynamic nonequilibrium structures such as living clusters, synchronized super-rotor structures or self-propelling molecules featuring a complexity which is rarely found outside of the living world. However, the precise mechanisms underlying the formation and dynamics of many of these structures are still barely understood, which is likely to hinge on the gaps in our understanding of how active colloids interact. In particular, besides showing comparatively short-ranged interactions which are well known from passive colloids (Van der Waals, electrostatic etc), active colloids show novel hydrodynamic interactions as well as phoretic and substrate-mediated 'osmotic' cross-interactions which hinge on the action of the phoretic field gradients which are induced by the colloids on other colloids in the system. The present article discusses the complexity and the intriguing properties of these interactions which in general are long-ranged, non-instantaneous, non-pairwise and non-reciprocal and which may serve as key ingredients for the design of future nonequilibrium colloidal materials. Besides providing a brief overview on the state of the art of our understanding of these interactions a key aim of this review is to emphasize open key questions and corresponding open challenges.
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Affiliation(s)
- Benno Liebchen
- Institute for Condensed Matter Physics, Technische Universität Darmstadt, 64289 Darmstadt, Germany
| | - Aritra K Mukhopadhyay
- Institute for Condensed Matter Physics, Technische Universität Darmstadt, 64289 Darmstadt, Germany
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16
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Ashaju A, Otten V, Wood JA, Lammertink RGH. Electrocatalytic Reaction Driven Flow: Role of pH in Flow Reversal. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2021; 125:24876-24886. [PMID: 34824659 PMCID: PMC8607504 DOI: 10.1021/acs.jpcc.1c06458] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Revised: 10/13/2021] [Indexed: 05/20/2023]
Abstract
Immobilized bimetallic structures generate fluid flow during electrocatalytic reactions with hydrogen peroxide, which is typically driven from the anodic metal to the cathodic metal similar to an electroosmotic flow. However, under low reactive regimes, the generated flow becomes fully reversed, which cannot be explained by the classical electroosmotic theory. This work aims at unraveling the origin and dynamics of this flow hysteresis through a combined experimental and numerical approach. The key electrocatalytic parameters that contribute to flow reversal are analyzed experimentally and numerically under low reactive regimes induced by bulk pH variations. The proton gradient that initiates chemomechanical actuation is probed with the use of fluorescence lifetime imaging. The fluid flow dynamics under reactive regimes are visualized by the use of particle tracking. Our numerical simulations elucidate the role of pH variations and additional ionic species (counterions) toward flow reversal. The combination of these techniques highlights the interplay between electrocatalytic and electrokinetic phenomena on the occurrence of flow reversal.
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Affiliation(s)
- Abimbola
A. Ashaju
- Soft Matter, Fluidics and Interfaces,
MESA+ Institute for Nanotechnology, University
of Twente, 7522NB Enschede, The Netherlands
| | - Veerle Otten
- Soft Matter, Fluidics and Interfaces,
MESA+ Institute for Nanotechnology, University
of Twente, 7522NB Enschede, The Netherlands
| | - Jeffery A. Wood
- Soft Matter, Fluidics and Interfaces,
MESA+ Institute for Nanotechnology, University
of Twente, 7522NB Enschede, The Netherlands
| | - Rob G. H. Lammertink
- Soft Matter, Fluidics and Interfaces,
MESA+ Institute for Nanotechnology, University
of Twente, 7522NB Enschede, The Netherlands
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17
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Wang W, Mallouk TE. A Practical Guide to Analyzing and Reporting the Movement of Nanoscale Swimmers. ACS NANO 2021; 15:15446-15460. [PMID: 34636550 DOI: 10.1021/acsnano.1c07503] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The recent invention of nanoswimmers-synthetic, powered objects with characteristic lengths in the range of 10-500 nm-has sparked widespread interest among scientists and the general public. As more researchers from different backgrounds enter the field, the study of nanoswimmers offers new opportunities but also significant experimental and theoretical challenges. In particular, the accurate characterization of nanoswimmers is often hindered by strong Brownian motion, convective effects, and the lack of a clear way to visualize them. When coupled with improper experimental designs and imprecise practices in data analysis, these issues can translate to results and conclusions that are inconsistent and poorly reproducible. This Perspective follows the course of a typical nanoswimmer investigation from synthesis through to applications and offers suggestions for best practices in reporting experimental details, recording videos, plotting trajectories, calculating and analyzing mobility, eliminating drift, and performing control experiments, in order to improve the reliability of the reported results.
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Affiliation(s)
- Wei Wang
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, China
| | - Thomas E Mallouk
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6243, United States
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Feuerstein L, Biermann CG, Xiao Z, Holm C, Simmchen J. Highly Efficient Active Colloids Driven by Galvanic Exchange Reactions. J Am Chem Soc 2021; 143:17015-17022. [PMID: 34523911 DOI: 10.1021/jacs.1c06400] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Micromotors are propelled by a variety of chemical reactions, with most of them being of catalytic nature. There are, however, systems based on redox reactions, which show clear benefits for efficiency. Here, we broaden the spectrum of suitable reactions to galvanic exchange processes, or an electrochemical replacement of a solid metal layer with dissolved ionic species of a more noble metal. We study the details of motility and the influence of different reaction parameters to conclude that these galvanophoretic processes circumvent several steps that lose efficiency in catalytic micromotors. Furthermore, we investigate the chemical process, the charge, and flow conditions that lead to this highly efficient new type of active motility. Toward a better understanding of the underlying processes, we propose an electrokinetic model that we numerically solve via finite elements.
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Affiliation(s)
- Linda Feuerstein
- Physical Chemistry, TU Dresden, Zellescher Weg 19, 01069 Dresden, Germany
| | - Carl Georg Biermann
- Institute for Computational Physics (ICP), Allmandring 3, 70569 Stuttgart, Germany
| | - Zuyao Xiao
- Physical Chemistry, TU Dresden, Zellescher Weg 19, 01069 Dresden, Germany
| | - Christian Holm
- Institute for Computational Physics (ICP), Allmandring 3, 70569 Stuttgart, Germany
| | - Juliane Simmchen
- Physical Chemistry, TU Dresden, Zellescher Weg 19, 01069 Dresden, Germany
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19
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Bioinspired micro/nanomotor with visible light energy-dependent forward, reverse, reciprocating, and spinning schooling motion. Proc Natl Acad Sci U S A 2021; 118:2104481118. [PMID: 34654746 DOI: 10.1073/pnas.2104481118] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/04/2021] [Indexed: 12/23/2022] Open
Abstract
In nature, microorganisms could sense the intensity of the incident visible light and exhibit bidirectional (positive or negative) phototaxis. However, it is still challenging to achieve the similar biomimetic phototaxis for the artificial micro/nanomotor (MNM) counterparts with the size from a few nanometers to a few micrometers. In this work, we report a fuel-free carbon nitride (C3N4)/polypyrrole nanoparticle (PPyNP)-based smart MNM operating in water, whose behavior resembles that of the phototactic microorganism. The MNM moves toward the visible light source under low illumination and away from it under high irradiation, which relies on the competitive interplay between the light-induced self-diffusiophoresis and self-thermophoresis mechanisms concurrently integrated into the MNM. Interestingly, the competition between these two mechanisms leads to a collective bidirectional phototaxis of an ensemble of MNMs under uniform illuminations and a spinning schooling behavior under a nonuniform light, both of which can be finely controllable by visible light energy. Our results provide important insights into the design of the artificial counterpart of the phototactic microorganism with sophisticated motion behaviors for diverse applications.
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20
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Zhou X, Wang S, Xian L, Shah ZH, Li Y, Lin G, Gao Y. Ionic Effects in Ionic Diffusiophoresis in Chemically Driven Active Colloids. PHYSICAL REVIEW LETTERS 2021; 127:168001. [PMID: 34723584 DOI: 10.1103/physrevlett.127.168001] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Revised: 01/20/2021] [Accepted: 09/15/2021] [Indexed: 06/13/2023]
Abstract
We study experimentally the effect of added salt in the phoretic motion of chemically driven colloidal particles. We show that the response of passive colloids to a fixed active colloid, be it attractive or repulsive, depends on the ionic strength, the ζ potential, and the size of the passive colloids. We further report that the direction of self-propulsion of Janus colloids can be reversed by decreasing their ζ potential below a critical value. By constructing an effective model that treats the colloid and ions as a whole subjected to the concentration field of generated ions and takes into account the joint effect of both generated and background ions in determining the Debye length, we demonstrate that the response of the passive colloids and the velocity of the Janus colloids can be quantitatively captured by this model under the ionic diffusiophoresis theory beyond the infinitely-thin-double-layer limit.
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Affiliation(s)
- Xuemao Zhou
- Institute for Advanced Study, Shenzhen University, 518060 Shenzhen, China
- Key Laboratory of Optoelectronic Device and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, 518060 Shenzhen, China
| | - Shuo Wang
- Institute for Advanced Study, Shenzhen University, 518060 Shenzhen, China
- Key Laboratory of Optoelectronic Device and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, 518060 Shenzhen, China
| | - Longbin Xian
- Institute for Advanced Study, Shenzhen University, 518060 Shenzhen, China
| | - Zameer Hussain Shah
- Institute for Advanced Study, Shenzhen University, 518060 Shenzhen, China
- Key Laboratory of Optoelectronic Device and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, 518060 Shenzhen, China
| | - Yurou Li
- Institute for Advanced Study, Shenzhen University, 518060 Shenzhen, China
| | - Guanhua Lin
- Institute for Advanced Study, Shenzhen University, 518060 Shenzhen, China
| | - Yongxiang Gao
- Institute for Advanced Study, Shenzhen University, 518060 Shenzhen, China
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21
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Lyu X, Liu X, Zhou C, Duan S, Xu P, Dai J, Chen X, Peng Y, Cui D, Tang J, Ma X, Wang W. Active, Yet Little Mobility: Asymmetric Decomposition of H 2O 2 Is Not Sufficient in Propelling Catalytic Micromotors. J Am Chem Soc 2021; 143:12154-12164. [PMID: 34339185 DOI: 10.1021/jacs.1c04501] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
A popular principle in designing chemical micromachines is to take advantage of asymmetric chemical reactions such as the catalytic decomposition of H2O2. Contrary to intuition, we use Janus micromotors half-coated with platinum (Pt) or catalase as an example to show that this ingredient is not sufficient in powering a micromotor into self-propulsion. In particular, by annealing a thin Pt film on a SiO2 microsphere, the resulting microsphere half-decorated with discrete Pt nanoparticles swims ∼80% more slowly than its unannealed counterpart in H2O2, even though they both catalytically produce comparable amounts of oxygen. Similarly, SiO2 microspheres half-functionalized with the enzyme catalase show negligible self-propulsion despite high catalytic activity toward decomposing H2O2. In addition to highlighting how surface morphology of a catalytic cap enables/disables a chemical micromotor, this study offers a refreshed perspective in understanding how chemistry powers nano- and microscopic objects (or not): our results are consistent with a self-electrophoresis mechanism that emphasizes the electrochemical decomposition of H2O2 over nonelectrochemical pathways. More broadly, our finding is a critical piece of the puzzle in understanding and designing nano- and micromachines, in developing capable model systems of active colloids, and in relating enzymes to active matter.
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Affiliation(s)
- Xianglong Lyu
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Xiaoxia Liu
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China.,Sauvage Laboratory for Smart Materials, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China
| | - Chao Zhou
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Shifang Duan
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Pengzhao Xu
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Jia Dai
- Department of Chemistry, The University of Hong Kong, Hong Kong 999077, China
| | - Xiaowen Chen
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Yixin Peng
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Donghao Cui
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Jinyao Tang
- Department of Chemistry, The University of Hong Kong, Hong Kong 999077, China.,State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Hong Kong 999077, China
| | - Xing Ma
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China.,Sauvage Laboratory for Smart Materials, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China.,Shenzhen Bay Laboratory, No. 9 Duxue Road, Shenzhen 518055, China
| | - Wei Wang
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
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22
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Abstract
Living systems use catalysis to achieve chemical transformations to comply with their needs in terms of energy and building blocks. The pH is a powerful means to regulate such processes, which also influences synthetic systems. In fact, the pH sensitivity of artificial photocatalysts, such as bismuth vanadate, bears the strong potential of flexibly influencing both the motion pattern and the speed of catalytic microswimmers, but it has rarely been investigated to date. In this work, we first present a comprehensive view of the motion behavior of differently shaped bismuth vanadate microswimmers, discuss influences, such as shape, pH, and conductivity of the solutions, and find that the motion pattern of the swimmers switches between upright and horizontal at their point of zero charge. We then apply an immobilizable hydroxypyrene derivative to our substrates to locally influence the pH of the solution by excited-state proton transfer. We find that the motion pattern of our swimmers is strongly influenced by this functionalization and a third motion mode, called tumbling, is introduced. Taking other effects, such as an increased surface roughness of the modified substrates, into account, we critically discuss possible future developments.
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23
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Katuri J, Uspal WE, Popescu MN, Sánchez S. Inferring non-equilibrium interactions from tracer response near confined active Janus particles. SCIENCE ADVANCES 2021; 7:7/18/eabd0719. [PMID: 33931441 PMCID: PMC8087409 DOI: 10.1126/sciadv.abd0719] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Accepted: 03/12/2021] [Indexed: 05/02/2023]
Abstract
Chemically active Janus particles sustain non-equilibrium spatial variations in the chemical composition of the suspending solution; these induce hydrodynamic flow and (self-)motility of the particles. Direct mapping of these fields has so far proven to be too challenging. Therefore, indirect methods are needed, e.g., deconvolving the response of "tracer" particles to the activity-induced fields. Here, we study experimentally the response of silica particles, sedimented at a wall, to active Pt/silica Janus particles. The latter are either immobilized at the wall, with the symmetry axis perpendicular or parallel to the wall, or motile. The experiments reveal complex effective interactions that are dependent on the configuration and on the state of motion of the active particle. Within the framework of a coarse-grained model, the behavior of tracers near an immobilized Janus particle can be captured qualitatively once activity-induced osmotic flows on the wall are considered.
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Affiliation(s)
- Jaideep Katuri
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Baldiri Reixac 10-12, 08028 Barcelona Spain.
| | - William E Uspal
- Department of Mechanical Engineering, University of Hawaii at Manoa, 2540 Dole Street, Holmes Hall 302, Honolulu, HI 96822, USA.
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569 Stuttgart, Germany
| | - Mihail N Popescu
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569 Stuttgart, Germany.
| | - Samuel Sánchez
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Baldiri Reixac 10-12, 08028 Barcelona Spain.
- Institució Catalana de Recerca i Estudis Avancats (ICREA), Pg. Lluís Companys 23, 08010 Bacelona, Spain
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24
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Neta PD, Tasinkevych M, Telo da Gama MM, Dias CS. Wetting of a solid surface by active matter. SOFT MATTER 2021; 17:2468-2478. [PMID: 33496301 DOI: 10.1039/d0sm02008g] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
A lattice model is used to study repulsive active particles at a planar surface. A rejection-free Kinetic Monte Carlo method is employed to characterize the wetting behaviour. The model predicts a motility-induced phase separation of active particles, and the bulk coexistence of dense liquid-like and dilute vapour-like steady states is determined. An "ensemble", with a varying number of particles, analogous to a grand canonical ensemble in equilibrium, is introduced. The formation and growth of the liquid film between the solid surface and the vapour phase is investigated. At constant activity, as the system is brought towards coexistence from the vapour side, the thickness of the adsorbed film exhibits a divergent behaviour regardless of the activity. This suggests a complete wetting scenario along the full coexistence curve.
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Affiliation(s)
- P D Neta
- Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal. and Centro de Física Teórica e Computacional, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
| | - M Tasinkevych
- Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal. and Centro de Física Teórica e Computacional, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
| | - M M Telo da Gama
- Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal. and Centro de Física Teórica e Computacional, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
| | - C S Dias
- Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal. and Centro de Física Teórica e Computacional, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
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25
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JAHANGIRI ALIREZA, RAJABI KALVANI PAYAM, SHAPOURI SAMANEH, SARI AMIRHOSSEIN, ŢĂLU ŞTEFAN, JALILI YOUSEFSEYED. Quantitative SEM characterisation of ceramic target prior and after magnetron sputtering: a case study of aluminium zinc oxide. J Microsc 2021; 281:190-201. [PMID: 32926411 PMCID: PMC7891359 DOI: 10.1111/jmi.12961] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2020] [Revised: 08/08/2020] [Accepted: 09/03/2020] [Indexed: 02/05/2023]
Abstract
Till now electron microscopy techniques have not been used to evaluate the plasma-target interactions undergone during the magnetron sputtering process. The destructive nature of this interaction severely alters the target microstructure. Utilising quantitative microscopy techniques can shed light on the complex plasma and solid-state processes involved which can ultimately lead to improved functional thin film deposition. As a representative functional material, aluminium-doped-zinc oxide (AZO) is an upcoming alternative to conventional transparent electrode wherein the process optimisation is of great importance. In this paper, we evaluate the pre- and post-sputter field emission scanning electron microscopy (FESEM) data for ceramic AZO target fabricated at three final sintering temperatures (1100°C, 1200°C and 1300°C). In all cases, grain boundaries are merged in addition to a visible reduction in the secondary phases which makes segmentation-based image analysis challenging. Through surface statistics (i.e. fractal dimension, autocorrelation length, texture aspect ratio and entropy) as a function of magnification we can quantify the electron microscopy image of the microstructure. We show that the plasma-microstructure interaction leads to an increase in autocorrelation length, texture aspect ratio and entropy for the optimum AZO ceramic sputtering target sintered at 1200°C. Furthermore, a maximum reduction in fractal dimension span (as determined by exponential regression) is also observed for 1200°C. In addition to the evaluation of plasma effects on sintering, our approach can provide a window towards understanding the underlying thin film growth mechanisms. We believe that this technique can be applied to the defect characterisation of a wide range of polycrystalline ceramic sputtering targets (e.g. ITO, CZTS, GAZO and so on) with the ultimate goal of improving the magnetron sputtering process and the resulting functional thin film. LAY DESCRIPTION: Magnetron sputtering allows scientists to make functional thin films on the order of the nanoscale. In this technique, atoms are plucked from a 'target' then placed onto a substrate forming a thin nanometric film: all thanks to magnets, a special power supply and the fourth state of matter (plasma). Understanding what is going on and how to make a 'good' thin film is important for making better light emitting diodes, solar cells and light sensors. Scientists use electron microscopy to see what is going on in the microstructure of the sputtered thin films to fine tune the sputtering recipe. Here, for the first time, we have applied electron microscopy to see the surface of the microstructure before and after magnetron sputtering. This will help us understanding the plasma-microstructure interaction allowing us to make more informed decisions when fine-tuning the sputtering process to get improved thin films. This is a case study of aluminium-doped zinc oxide (AZO) target that could potentially replace indium tin oxide (ITO), which is widely used as a transparent electrode in devices involving light and electricity. In this case, improved characteristics would be lower electrical resistivity and higher transmission of light. We show that it is possible to use a mathematical description (e.g. the fractal dimension) of the scanning electron microscopy picture to show a link between the target surface and the functional properties. Simple explanation of fractal dimensions by Sixty Symbols ○ https://www.youtube.com/watch?v=cmBljeC79Ls Experimental demonstration of magnetron sputtering by The Thought Emporium ○ https://www.youtube.com/watch?v=Cyu7etM-0Ko Introductory video on magnetron sputtering by Applied Science ○ https://www.youtube.com/watch?v=9OEz_e9C4KM Demonstration of AZO target fabrication and sputtering by Pradhyut Rajjkumar ○ https://www.youtube.com/watch?v=kTLaTJfNX3c Simple explanation of a DIY SEM by Applied Science ○ https://www.youtube.com/watch?v=VdjYVF4a6iU.
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Affiliation(s)
- ALI REZA JAHANGIRI
- NanoLundLund UniversityBox 118, 22100LundSweden
- Department of Physics, Faculty of Science, Science and Research BranchIslamic Azad UniversityTehranIran
- Plasma Physics Research Centre, Science and Research BranchIslamic Azad UniversityTehranIran
- Nano‐Optoelectronics Laboratory, Sheykh Bahaee Research Complex, Science and Research BranchIslamic Azad UniversityTehranIran
| | - PAYAM RAJABI KALVANI
- Department of Physics, Faculty of Science, Science and Research BranchIslamic Azad UniversityTehranIran
- Plasma Physics Research Centre, Science and Research BranchIslamic Azad UniversityTehranIran
- Nano‐Optoelectronics Laboratory, Sheykh Bahaee Research Complex, Science and Research BranchIslamic Azad UniversityTehranIran
| | - SAMANEH SHAPOURI
- Department of Physics, Faculty of Science, Science and Research BranchIslamic Azad UniversityTehranIran
- Plasma Physics Research Centre, Science and Research BranchIslamic Azad UniversityTehranIran
- Nano‐Optoelectronics Laboratory, Sheykh Bahaee Research Complex, Science and Research BranchIslamic Azad UniversityTehranIran
| | - AMIRHOSSEIN SARI
- Department of Physics, Faculty of Science, Science and Research BranchIslamic Azad UniversityTehranIran
- Plasma Physics Research Centre, Science and Research BranchIslamic Azad UniversityTehranIran
| | - ŞTEFAN ŢĂLU
- The Directorate of Research, Development and Innovation Management (DMCDI)Technical University of Cluj‐NapocaCluj‐NapocaClujRomania
| | - YOUSEF SEYED JALILI
- Department of Physics, Faculty of Science, Science and Research BranchIslamic Azad UniversityTehranIran
- Plasma Physics Research Centre, Science and Research BranchIslamic Azad UniversityTehranIran
- Nano‐Optoelectronics Laboratory, Sheykh Bahaee Research Complex, Science and Research BranchIslamic Azad UniversityTehranIran
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26
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Domínguez A, Popescu MN, Rohwer CM, Dietrich S. Self-Motility of an Active Particle Induced by Correlations in the Surrounding Solution. PHYSICAL REVIEW LETTERS 2020; 125:268002. [PMID: 33449719 DOI: 10.1103/physrevlett.125.268002] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Revised: 09/09/2020] [Accepted: 10/30/2020] [Indexed: 06/12/2023]
Abstract
Current models of phoretic transport rely on molecular forces creating a "diffuse" particle-fluid interface. We investigate theoretically an alternative mechanism, in which a diffuse interface emerges solely due to a nonvanishing correlation length of the surrounding solution. This mechanism can drive self-motility of a chemically active particle. Numerical estimates indicate that the velocity can reach micrometers per second. The predicted phenomenology includes a bilinear dependence of the velocity on the activity and a possible double velocity reversal upon varying the correlation length.
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Affiliation(s)
- Alvaro Domínguez
- Física Teórica, Universidad de Sevilla, Apdo. 1065, 41080 Sevilla, Spain
- Instituto Carlos I de Física Teórica y Computacional, 18071 Granada, Spain
| | - M N Popescu
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstraße 3, 70569 Stuttgart, Germany
| | - C M Rohwer
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstraße 3, 70569 Stuttgart, Germany
- IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany
- Department of Mathematics & Applied Mathematics, University of Cape Town, 7701 Rondebosch, Cape Town, South Africa
| | - S Dietrich
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstraße 3, 70569 Stuttgart, Germany
- IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany
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27
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Ketzetzi S, de Graaf J, Kraft DJ. Diffusion-Based Height Analysis Reveals Robust Microswimmer-Wall Separation. PHYSICAL REVIEW LETTERS 2020; 125:238001. [PMID: 33337216 DOI: 10.1103/physrevlett.125.238001] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Accepted: 10/08/2020] [Indexed: 06/12/2023]
Abstract
Microswimmers typically move near walls, which can strongly influence their motion. However, direct experimental measurements of swimmer-wall separation remain elusive to date. Here, we determine this separation for model catalytic microswimmers from the height dependence of the passive component of their mean-squared displacement. We find that swimmers exhibit "ypsotaxis," a tendency to assume a fixed height above the wall for a range of salt concentrations, swimmer surface charges, and swimmer sizes. Our findings indicate that ypsotaxis is activity induced, posing restrictions on future modeling of their still-debated propulsion mechanism.
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Affiliation(s)
- Stefania Ketzetzi
- Soft Matter Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, Netherlands
| | - Joost de Graaf
- Institute for Theoretical Physics, Center for Extreme Matter and Emergent Phenomena, Utrecht University, Princetonplein 5, 3584 CC Utrecht, Netherlands
| | - Daniela J Kraft
- Soft Matter Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, Netherlands
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28
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Seo M, Park S, Lee D, Lee H, Kim SJ. Continuous and spontaneous nanoparticle separation by diffusiophoresis. LAB ON A CHIP 2020; 20:4118-4127. [PMID: 32909576 DOI: 10.1039/d0lc00593b] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
The separation of nanoparticles has drawn critical attention in various microfluidic applications including chemical analysis, diagnostics and environmental monitoring. Thus, a number of nanoparticle separation methods have been extensively proposed. However, most of the conventional methods require complicated structured devices, expensive manufacturing processes, and external power sources. While a spontaneous diffusiophoretic separation device based on an ion exchange mechanism could overcome such drawbacks, the recovery of separated particles and the inevitable development of an acidic environment due to the release of H+ from the cation exchange membrane limit its practical applicability. Therefore, in this work, we present a simple but robust nanoparticle separation method based on spontaneously induced diffusiophoresis, which is operated in a continuous manner to overcome the limitations of conventional methods. First, we confirmed that the particle exclusion distance followed the previously developed scaling law of diffusiophoresis. Consequently, we demonstrated the separation of nanoparticles of 40 nm, 200 nm and 2 μm diameter by utilizing the fact that the exclusion distances of various particles were proportional to their diffusiophoretic mobility. Furthermore, the use of Tris buffer increased the diffusiophoretic migration of nanoparticles due to the enhanced concentration gradient, and enabled the produced solution to be compatible with pH-sensitive bio-samples. Therefore, we expect this continuous and spontaneous diffusiophoretic separation platform to be useful in practical applications for analyzing various nano-meter scale bio-particles.
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Affiliation(s)
- Myungjin Seo
- Department of Electrical and Computer Engineering, Seoul National University, Seoul 08826, Republic of Korea.
| | - Sungmin Park
- Department of Electrical and Computer Engineering, Seoul National University, Seoul 08826, Republic of Korea.
| | - Dokeun Lee
- Department of Electrical and Computer Engineering, Seoul National University, Seoul 08826, Republic of Korea.
| | - Hyomin Lee
- Department of Chemical and Biological Engineering, Jeju National University, Jeju 63243, Republic of Korea.
| | - Sung Jae Kim
- Department of Electrical and Computer Engineering, Seoul National University, Seoul 08826, Republic of Korea. and Nano Systems Institute, Seoul National University, Seoul 08826, Republic of Korea and Inter-university Semiconductor Research Center, Seoul National University, Seoul 08826, Republic of Korea
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29
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Arqué X, Andrés X, Mestre R, Ciraulo B, Ortega Arroyo J, Quidant R, Patiño T, Sánchez S. Ionic Species Affect the Self-Propulsion of Urease-Powered Micromotors. RESEARCH 2020; 2020:2424972. [PMID: 32803169 PMCID: PMC7404610 DOI: 10.34133/2020/2424972] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Accepted: 06/17/2020] [Indexed: 11/18/2022]
Abstract
Enzyme-powered motors self-propel through the catalysis of in situ bioavailable fuels, which makes them excellent candidates for biomedical applications. However, fundamental issues like their motion in biological fluids and the understanding of the propulsion mechanism are critical aspects to be tackled before a future application in biomedicine. Herein, we investigated the physicochemical effects of ionic species on the self-propulsion of urease-powered micromotors. Results showed that the presence of PBS, NaOH, NaCl, and HEPES reduced self-propulsion of urease-powered micromotors pointing towards ion-dependent mechanisms of motion. We studied the 3D motion of urease micromotors using digital holographic microscopy to rule out any motor-surface interaction as the cause of motion decay when salts are present in the media. In order to protect and minimize the negative effect of ionic species on micromotors' performance, we coated the motors with methoxypolyethylene glycol amine (mPEG) showing higher speed compared to noncoated motors at intermediate ionic concentrations. These results provide new insights into the mechanism of urease-powered micromotors, study the effect of ionic media, and contribute with potential solutions to mitigate the reduction of mobility of enzyme-powered micromotors.
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Affiliation(s)
- Xavier Arqué
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Baldiri i Reixac 10-12, 08028 Barcelona, Spain
| | - Xavier Andrés
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Baldiri i Reixac 10-12, 08028 Barcelona, Spain
| | - Rafael Mestre
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Baldiri i Reixac 10-12, 08028 Barcelona, Spain
| | - Bernard Ciraulo
- Institute of Photonic Sciences (ICFO), The Barcelona Institute of Science and Technology, Carl Friedrich Gauss 3, 08860 Castelldefels, Barcelona, Spain
| | - Jaime Ortega Arroyo
- Institute of Photonic Sciences (ICFO), The Barcelona Institute of Science and Technology, Carl Friedrich Gauss 3, 08860 Castelldefels, Barcelona, Spain
| | - Romain Quidant
- Institute of Photonic Sciences (ICFO), The Barcelona Institute of Science and Technology, Carl Friedrich Gauss 3, 08860 Castelldefels, Barcelona, Spain.,Institució Catalana de Recerca i Estudis Avançats (ICREA), Pg. Lluís Companys 23, 08010 Barcelona, Spain
| | - Tania Patiño
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Baldiri i Reixac 10-12, 08028 Barcelona, Spain.,Chemistry Department, University of Rome, Tor Vergata, Via della Ricerca Scientifica, 00133 Rome, Italy
| | - Samuel Sánchez
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Baldiri i Reixac 10-12, 08028 Barcelona, Spain.,Institució Catalana de Recerca i Estudis Avançats (ICREA), Pg. Lluís Companys 23, 08010 Barcelona, Spain
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30
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Sridhar V, Park BW, Guo S, van Aken PA, Sitti M. Multiwavelength-Steerable Visible-Light-Driven Magnetic CoO-TiO 2 Microswimmers. ACS APPLIED MATERIALS & INTERFACES 2020; 12:24149-24155. [PMID: 32351105 PMCID: PMC7256931 DOI: 10.1021/acsami.0c06100] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
While current light-driven microswimmers require high-intensity light, UV light, or toxic fuels to propel them, powering them with low-intensity UV-free visible light without fuels is essential to enable their potential high-impact applications. Therefore, in this study, a new material for light-driven microswimmers in the form of CoO is introduced. Janus CoO-TiO2 microswimmers powered with low-intensity, UV-free visible light inside water without using any toxic fuels like H2O2 is proposed. The microswimmers show propulsion under full spectrum of visible light with 17 times lower intensity than the mean solar intensity. They propel by breaking down water into oxygen and oxide radicals, which enables their potential applications for photocatalysis and drug delivery. The microswimmers are multiwavelength responsive, from the ultraviolet to the infrared region. The direction of swimming changes with the change in the illumination from the visible to UV light. In addition to being responsive, they are wavelength steerable and exhibit inherent magnetic properties enabling magnetic steering control of the CoO-TiO2 microswimmers. Thus, these microswimmers, which are propelled under low-intensity visible light, have direction-changing capability using light of different wavelengths, and have steering control capability by external magnetic fields, could be used in future potential applications, such as active and local cargo delivery, active photocatalysis, and hydrogen evolution.
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Affiliation(s)
- Varun Sridhar
- Physical
Intelligence Department, Max Planck Institute
for Intelligent Systems, 70569 Stuttgart, Germany
| | - Byung-Wook Park
- Department
of Chemical Engineering, Youngstown State
University, Youngstown, Ohio 44555, United States
| | - Surong Guo
- Stuttgart
Center for Electron Microscopy, Max Planck
Institute for Solid State Research, 70569 Stuttgart, Germany
| | - Peter A. van Aken
- Stuttgart
Center for Electron Microscopy, Max Planck
Institute for Solid State Research, 70569 Stuttgart, Germany
| | - Metin Sitti
- Physical
Intelligence Department, Max Planck Institute
for Intelligent Systems, 70569 Stuttgart, Germany
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Gompper G, Winkler RG, Speck T, Solon A, Nardini C, Peruani F, Löwen H, Golestanian R, Kaupp UB, Alvarez L, Kiørboe T, Lauga E, Poon WCK, DeSimone A, Muiños-Landin S, Fischer A, Söker NA, Cichos F, Kapral R, Gaspard P, Ripoll M, Sagues F, Doostmohammadi A, Yeomans JM, Aranson IS, Bechinger C, Stark H, Hemelrijk CK, Nedelec FJ, Sarkar T, Aryaksama T, Lacroix M, Duclos G, Yashunsky V, Silberzan P, Arroyo M, Kale S. The 2020 motile active matter roadmap. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:193001. [PMID: 32058979 DOI: 10.1088/1361-648x/ab6348] [Citation(s) in RCA: 150] [Impact Index Per Article: 37.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Activity and autonomous motion are fundamental in living and engineering systems. This has stimulated the new field of 'active matter' in recent years, which focuses on the physical aspects of propulsion mechanisms, and on motility-induced emergent collective behavior of a larger number of identical agents. The scale of agents ranges from nanomotors and microswimmers, to cells, fish, birds, and people. Inspired by biological microswimmers, various designs of autonomous synthetic nano- and micromachines have been proposed. Such machines provide the basis for multifunctional, highly responsive, intelligent (artificial) active materials, which exhibit emergent behavior and the ability to perform tasks in response to external stimuli. A major challenge for understanding and designing active matter is their inherent nonequilibrium nature due to persistent energy consumption, which invalidates equilibrium concepts such as free energy, detailed balance, and time-reversal symmetry. Unraveling, predicting, and controlling the behavior of active matter is a truly interdisciplinary endeavor at the interface of biology, chemistry, ecology, engineering, mathematics, and physics. The vast complexity of phenomena and mechanisms involved in the self-organization and dynamics of motile active matter comprises a major challenge. Hence, to advance, and eventually reach a comprehensive understanding, this important research area requires a concerted, synergetic approach of the various disciplines. The 2020 motile active matter roadmap of Journal of Physics: Condensed Matter addresses the current state of the art of the field and provides guidance for both students as well as established scientists in their efforts to advance this fascinating area.
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Affiliation(s)
- Gerhard Gompper
- Theoretical Soft Matter and Biophysics, Institute of Complex Systems and Institute for Advanced Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany
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Wang W, Lv X, Moran JL, Duan S, Zhou C. A practical guide to active colloids: choosing synthetic model systems for soft matter physics research. SOFT MATTER 2020; 16:3846-3868. [PMID: 32285071 DOI: 10.1039/d0sm00222d] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Synthetic active colloids that harvest energy stored in the environment and swim autonomously are a popular model system for active matter. This emerging field of research sits at the intersection of materials chemistry, soft matter physics, and engineering, and thus cross-talk among researchers from different backgrounds becomes critical yet difficult. To facilitate this interdisciplinary communication, and to help soft matter physicists with choosing the best model system for their research, we here present a tutorial review article that describes, in appropriate detail, six experimental systems of active colloids commonly found in the physics literature. For each type, we introduce their background, material synthesis and operating mechanisms and notable studies from the soft matter community, and comment on their respective advantages and limitations. In addition, the main features of each type of active colloid are summarized into two useful tables. As materials chemists and engineers, we intend for this article to serve as a practical guide, so those who are not familiar with the experimental aspects of active colloids can make more informed decisions and maximize their creativity.
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Affiliation(s)
- Wei Wang
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, China.
| | - Xianglong Lv
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, China.
| | - Jeffrey L Moran
- Department of Mechanical Engineering, George Mason University, Fairfax, USA
| | - Shifang Duan
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, China.
| | - Chao Zhou
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, China.
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Zhang J, Zhan K, Wang S, Hou X. Soft interface design for electrokinetic energy conversion. SOFT MATTER 2020; 16:2915-2927. [PMID: 32159200 DOI: 10.1039/c9sm02506e] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The exploitation and utilization of renewable clean energy is of great significance to the sustainable development of society. Electrokinetic energy conversion (EKEC) based on micro/nanochannels is expected to provide immense potential for ocean energy harvesting, self-powered micro/nanodevices, and small portable power supplies through converting environmental energy into electrical energy. Herein, aiming to get a deeper understanding of EKEC based on micro/nanochannels, several classic theoretical models and corresponding calculation equations are introduced briefly. For high efficiency energy conversion, it is essential to clearly discuss the interface properties between the inner surface of the channel and the bulk electrolyte solution. Therefore, we put forward soft interface designs of solid-liquid and liquid-liquid interfaces, and summarize their recent progress. In addition, the different applications of EKEC, harvesting from environmental energy, are further discussed. We hope that this review will attract more scientists' attention to transform the experimental results of EKEC systems in the lab into available products on shelves.
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Affiliation(s)
- Jian Zhang
- Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen University, No. 422, Siming South Road, Xiamen 361005, Fujian, P. R. China.
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Wang J, Xiong Z, Liu M, Li XM, Zheng J, Zhan X, Ding W, Chen J, Li X, Li XD, Feng SP, Tang J. Rational Design of Reversible Redox Shuttle for Highly Efficient Light-Driven Microswimmer. ACS NANO 2020; 14:3272-3280. [PMID: 32125822 DOI: 10.1021/acsnano.9b08799] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The light-driven micro/nanomotor (LMNM) is machinery that harvests photon energy and generates self-propulsion in varieties of liquid media. Though visions are made that these tiny swimming machines can serve future medicine for accurate drug delivery and noninvasive microsurgery, their biomedical application is still impeded by the insufficient propulsion efficiency. Here we provide a holistic model of LMNM by considering (i) photovoltaic, (ii) electrochemical, and (iii) electrokinetic processes therein. Such a quantitative model revealed the pivotal role of reaction kinetics and diffusion properties of shuttle ions in the propulsion efficiency of LMNM. With the guidance of this model, a group of ferrocene-based reversible redox shuttles, which generate slow-diffusion ions, was identified, showcasing a high locomotion velocity of ∼500 μm/s (∼100 body length per second) at an ultralow concentration (70 μM). Owing to the in-depth understanding of the fundamental energy conversion processes in LMNM, we anticipate that the development of other high-performance supporting chemicals and LMNM systems will be greatly motivated, foreseeing the advent of LMNM systems with superior efficiency.
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Affiliation(s)
- Jizhuang Wang
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
- College of Chemistry and Materials Science, Jinan University, Guangzhou 510632, P. R. China
| | - Ze Xiong
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Ming Liu
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Xiao-Meng Li
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Jing Zheng
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Xiaojun Zhan
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Weiting Ding
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Jianan Chen
- Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Xuechen Li
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Xiang David Li
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Shien-Ping Feng
- Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Jinyao Tang
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
- State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
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De Corato M, Arqué X, Patiño T, Arroyo M, Sánchez S, Pagonabarraga I. Self-Propulsion of Active Colloids via Ion Release: Theory and Experiments. PHYSICAL REVIEW LETTERS 2020; 124:108001. [PMID: 32216443 DOI: 10.1103/physrevlett.124.108001] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Accepted: 02/11/2020] [Indexed: 06/10/2023]
Abstract
We study the self-propulsion of a charged colloidal particle that releases ionic species using theory and experiments. We relax the assumptions of thin Debye length and weak nonequilibrium effects assumed in classical phoretic models. This leads to a number of unexpected features that cannot be rationalized considering the classic phoretic framework: an active particle can reverse the direction of motion by increasing the rate of ion release and can propel even with zero surface charge. Our theory predicts that there are optimal conditions for self-propulsion and a novel regime in which the velocity is insensitive to the background electrolyte concentration. The theoretical results quantitatively capture the salt-dependent velocity measured in our experiments using active colloids that propel by decomposing urea via a surface enzymatic reaction.
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Affiliation(s)
- Marco De Corato
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Baldiri Reixac 10-12, 08028 Barcelona Spain
| | - Xavier Arqué
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Baldiri Reixac 10-12, 08028 Barcelona Spain
| | - Tania Patiño
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Baldiri Reixac 10-12, 08028 Barcelona Spain
- Chemistry Department, University of Rome, Tor Vergata, Via della Ricerca Scientifica, 00133 Rome, Italy
| | - Marino Arroyo
- LaCàN, Universitat Politècnica de Catalunya-BarcelonaTech, 08034 Barcelona, Spain; Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Baldiri Reixac 10-12, 08028 Barcelona, Spain; and Centre Internacional de Mètodes Numèrics en Enginyeria (CIMNE), 08034 Barcelona, Spain
| | - Samuel Sánchez
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Baldiri Reixac 10-12, 08028 Barcelona Spain; and Institució Catalana de Recerca i Estudis Avançats (ICREA), Pg. Lluís Companys 23, 08010 Barcelona, Spain
| | - Ignacio Pagonabarraga
- Departament de Física de la Matèria Condensada, Universitat de Barcelona, C. Martí Franquès 1, 08028 Barcelona, Spain; University of Barcelona Institute of Complex Systems (UBICS), Universitat de Barcelona, 08028 Barcelona, Spain; and CECAM, Centre Européen de Calcul Atomique et Moléculaire, École Polytechnique Fédérale de Lasuanne (EPFL), Batochime, Avenue Forel 2,1015 Lausanne, Switzerland
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Wang Y, Duan W, Zhou C, Liu Q, Gu J, Ye H, Li M, Wang W, Ma X. Phoretic Liquid Metal Micro/Nanomotors as Intelligent Filler for Targeted Microwelding. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1905067. [PMID: 31664739 DOI: 10.1002/adma.201905067] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2019] [Revised: 10/03/2019] [Indexed: 05/23/2023]
Abstract
Micro/nanomotors (MNMs) have emerged as active micro/nanoplatforms that can move and perform functions at small scales. Much of their success, however, hinges on the use of functional properties of new materials. Liquid metals (LMs), due to their good electrical conductivity, biocompatibility, and flexibility, have attracted considerable attentions in the fields of flexible electronics, biomedicine, and soft robotics. The design and construction of LM-based motors is therefore a research topic with tremendous prospects, however current approaches are mostly limited to macroscales. Here, the fabrication of an LM-MNM (made of Galinstan, a gallium-indium-tin alloy) is reported and its potential application as an on-demand, self-targeting welding filler is demonstrated. These LM-MNMs (as small as a few hundred nanometers) are half-coated with a thin layer of platinum (Pt) and move in H2 O2 via self-electrophoresis. In addition, the LM-MNMs roaming in a silver nanowire network can move along the nanowires and accumulate at the contact junctions where they become fluidic and achieve junction microwelding at room temperature by reacting with acid vapor. This work presents an intelligent and soft nanorobot capable of repairing circuits by welding at small scales, thus extending the pool of available self-propelled MNMs and introducing new applications.
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Affiliation(s)
- Yong Wang
- State Key Laboratory of Advanced Welding and Joining (Shenzhen) and Flexible Printed Electronic Technology Center, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China
| | - Wendi Duan
- State Key Laboratory of Advanced Welding and Joining (Shenzhen) and Flexible Printed Electronic Technology Center, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China
| | - Chao Zhou
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China
| | - Qing Liu
- State Key Laboratory of Advanced Welding and Joining (Shenzhen) and Flexible Printed Electronic Technology Center, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China
| | - Jiahui Gu
- State Key Laboratory of Advanced Welding and Joining (Shenzhen) and Flexible Printed Electronic Technology Center, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China
| | - Heng Ye
- State Key Laboratory of Advanced Welding and Joining (Shenzhen) and Flexible Printed Electronic Technology Center, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China
| | - Mingyu Li
- State Key Laboratory of Advanced Welding and Joining (Shenzhen) and Flexible Printed Electronic Technology Center, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China
| | - Wei Wang
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China
| | - Xing Ma
- State Key Laboratory of Advanced Welding and Joining (Shenzhen) and Flexible Printed Electronic Technology Center, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China
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de Graaf J, Samin S. Self-thermoelectrophoresis at low salinity. SOFT MATTER 2019; 15:7219-7236. [PMID: 31478044 DOI: 10.1039/c9sm00886a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
A locally heated Janus colloid can achieve motion in an electrolyte by an effect known as self-thermo(di)electrophoresis. We numerically study the self-propulsion of such a "hot swimmer" in a monovalent electrolyte using the finite-element method and analytic theory. The effect of electrostatic screening for intermediate and large Debye lengths is charted and we report on the fluid flow generated by self-thermoelectrophoresis. We obtain excellent agreement between our analytic theory and numerical calculations in the limit of high salinity, validating our approach. At low salt concentrations, we employ Teubner's integral formalism to arrive at expressions for the speed, which agree semi-quantitatively with our numerical results for conducting swimmers. This lends credibility to the remarkably high swim speed at very low ionic strength, which we numerically obtain for a fully insulating swimmer. We also report on hot swimmers with a mixed electrostatic boundary conditions. Our results should benefit the realization and analysis of further experiments on thermo(di)electrophoretic swimmers.
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Affiliation(s)
- Joost de Graaf
- Institute for Theoretical Physics, Center for Extreme Matter and Emergent Phenomena, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
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Campbell AI, Ebbens SJ, Illien P, Golestanian R. Experimental observation of flow fields around active Janus spheres. Nat Commun 2019; 10:3952. [PMID: 31477703 PMCID: PMC6718378 DOI: 10.1038/s41467-019-11842-1] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Accepted: 07/30/2019] [Indexed: 12/13/2022] Open
Abstract
The phoretic mechanisms at stake in the propulsion of asymmetric colloids have been the subject of debates during the past years. In particular, the importance of electrokinetic effects on the motility of Pt-PS Janus sphere was recently discussed. Here, we probe the hydrodynamic flow field around a catalytically active colloid using particle tracking velocimetry both in the freely swimming state and when kept stationary with an external force. Our measurements provide information about the fluid velocity in the vicinity of the surface of the colloid, and confirm a mechanism for propulsion that was proposed recently. In addition to offering a unified understanding of the nonequilibrium interfacial transport processes at stake, our results open the way to a thorough description of the hydrodynamic interactions between such active particles and understanding their collective dynamics.
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Affiliation(s)
- Andrew I Campbell
- Department of Chemical and Biological Engineering, University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK
| | - Stephen J Ebbens
- Department of Chemical and Biological Engineering, University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK.
| | - Pierre Illien
- Sorbonne Université, CNRS, Laboratoire PHENIX, 4 place Jussieu, 75005, Paris, France
| | - Ramin Golestanian
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), 37077, Göttingen, Germany. .,Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford, OX1 3PU, UK.
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39
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Singh R, Adhikari R, Cates ME. Competing chemical and hydrodynamic interactions in autophoretic colloidal suspensions. J Chem Phys 2019; 151:044901. [DOI: 10.1063/1.5090179] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Affiliation(s)
- Rajesh Singh
- DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, United Kingdom
| | - R. Adhikari
- DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, United Kingdom
- The Institute of Mathematical Sciences-HBNI, CIT Campus, Chennai 600113, India
| | - M. E. Cates
- DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, United Kingdom
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Speck T. Thermodynamic approach to the self-diffusiophoresis of colloidal Janus particles. Phys Rev E 2019; 99:060602. [PMID: 31330705 DOI: 10.1103/physreve.99.060602] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2019] [Indexed: 01/02/2023]
Abstract
Most available theoretical predictions for the self-diffusiophoretic motion of colloidal particles are based on the hydrodynamic thin boundary layer approximation in combination with a solvent body force due to a self-generated local solute gradient. This gradient is enforced through specifying boundary conditions, typically without accounting for the thermodynamic cost to maintain the gradient. Here, we present an alternative thermodynamic approach that exploits a direct link between dynamics and entropy production: the local detailed balance condition. We study two cases: First, we revisit self-propulsion in a demixing binary solvent. At variance with a slip velocity, we find that propulsion is due to forces at the poles that are perpendicular to the particle surface. Second, for catalytic swimmers driven through liberating chemical free energy we recover previous expressions. In both cases we argue that propulsion is due to asymmetric dissipation and not simply due to an asymmetric concentration of molecular solutes.
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Affiliation(s)
- Thomas Speck
- Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7-9, 55128 Mainz, Germany
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41
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Kuron M, Stärk P, Holm C, de Graaf J. Hydrodynamic mobility reversal of squirmers near flat and curved surfaces. SOFT MATTER 2019; 15:5908-5920. [PMID: 31282522 DOI: 10.1039/c9sm00692c] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Self-propelled particles have been experimentally shown to orbit spherical obstacles and move along surfaces. Here, we theoretically and numerically investigate this behavior for a hydrodynamic squirmer interacting with spherical objects and flat walls using three different methods of approximately solving the Stokes equations: The method of reflections, which is accurate in the far field; lubrication theory, which describes the close-to-contact behavior; and a lattice Boltzmann solver that accurately accounts for near-field flows. The method of reflections predicts three distinct behaviors: orbiting/sliding, scattering, and hovering, with orbiting being favored for lower curvature as in the literature. Surprisingly, it also shows backward orbiting/sliding for sufficiently strong pushers, caused by fluid recirculation in the gap between the squirmer and the obstacle leading to strong forces opposing forward motion. Lubrication theory instead suggests that only hovering is a stable point for the dynamics. We therefore employ lattice Boltzmann to resolve this discrepancy and we qualitatively reproduce the richer far-field predictions. Our results thus provide insight into a possible mechanism of mobility reversal mediated solely through hydrodynamic interactions with a surface.
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Affiliation(s)
- Michael Kuron
- Institute for Computational Physics, University of Stuttgart, Allmandring 3, 70569 Stuttgart, Germany.
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Bayati P, Popescu MN, Uspal WE, Dietrich S, Najafi A. Dynamics near planar walls for various model self-phoretic particles. SOFT MATTER 2019; 15:5644-5672. [PMID: 31245803 DOI: 10.1039/c9sm00488b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
For chemically active particles suspended in a liquid solution and moving by self-phoresis, the dynamics near chemically inert, planar walls is studied theoretically by employing various choices for the activity function, i.e., the spatial distribution of the sites where various chemical reactions take place. We focus on the case of solutions composed of electrically neutral species. This analysis extends previous studies of the case that the chemical activity can be modeled effectively as the release of a "product" molecular species from parts of the surface of the particle by accounting for annihilation of the product molecules by chemical reactions, either on the rest of the surface of the particle or in the volume of the surrounding solution. We show that, for the models considered here, the emergence of "sliding" and "hovering" wall-bound states is a generic, robust feature. However, the details of these states, such as the range of parameters within which they occur, depend on the specific model for the activity function. Additionally, in certain cases there is a reversal of the direction of the motion compared to the one observed if the particle is far away from the wall. We have also studied the changes of the dynamics induced by a direct interaction between the particle and the wall by including a short-ranged repulsive component to the interaction in addition to the steric one (a procedure often employed in numerical simulations of active colloids). Upon increasing the strength of this additional component, while keeping its range fixed, significant qualitative changes occur in the phase portraits of the dynamics near the wall: for sufficiently strong short-ranged repulsion, the sliding steady states of the dynamics are transformed into hovering states. Furthermore, our studies provide evidence for an additional "oscillatory" wall-bound steady state of motion for chemically active particles due to a strong, short-ranged, and direct repulsion. This kind of particle translates along the wall at a distance from it which oscillates between a minimum and a maximum.
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Affiliation(s)
- Parvin Bayati
- Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran.
| | - Mihail N Popescu
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569 Stuttgart, Germany and IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany
| | - William E Uspal
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569 Stuttgart, Germany and IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany and Department of Mechanical Engineering, University of Hawai'i at Manoa, 2540 Dole Street, Holmes 302, Honolulu, HI 96822, USA
| | - S Dietrich
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569 Stuttgart, Germany and IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany
| | - Ali Najafi
- Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran. and Research Center for Basic Sciences & Modern Technologies (RBST), Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
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Affiliation(s)
- P. Bayati
- Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
| | - A. Najafi
- Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
- Research Center for Basic Sciences & Modern Technologies (RBST), Institute for Advanced Studies in Basic Sciences, Zanjan, Iran
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Chen X, Zhou C, Wang W. Colloidal Motors 101: A Beginner's Guide to Colloidal Motor Research. Chem Asian J 2019; 14:2388-2405. [DOI: 10.1002/asia.201900377] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2019] [Revised: 04/09/2019] [Indexed: 12/24/2022]
Affiliation(s)
- Xi Chen
- School of Materials Science and EngineeringHarbin Institute of Technology (Shenzhen) G 908, HIT Campus, Xili University Town Shenzhen Guangdong China
| | - Chao Zhou
- School of Materials Science and EngineeringHarbin Institute of Technology (Shenzhen) G 908, HIT Campus, Xili University Town Shenzhen Guangdong China
| | - Wei Wang
- School of Materials Science and EngineeringHarbin Institute of Technology (Shenzhen) G 908, HIT Campus, Xili University Town Shenzhen Guangdong China
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Günther JP, Majer G, Fischer P. Absolute diffusion measurements of active enzyme solutions by NMR. J Chem Phys 2019; 150:124201. [PMID: 30927887 DOI: 10.1063/1.5086427] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The diffusion of enzymes is of fundamental importance for many biochemical processes. Enhanced or directed enzyme diffusion can alter the accessibility of substrates and the organization of enzymes within cells. Several studies based on fluorescence correlation spectroscopy report enhanced diffusion of enzymes upon interaction with their substrate or inhibitor. In this context, major importance is given to the enzyme fructose-bisphosphate aldolase, for which enhanced diffusion has been reported even though the catalysed reaction is endothermic. Additionally, enhanced diffusion of tracer particles surrounding the active aldolase enzymes has been reported. These studies suggest that active enzymes can act as chemical motors that self-propel and give rise to enhanced diffusion. However, fluorescence studies of enzymes can, despite several advantages, suffer from artefacts. Here, we show that the absolute diffusion coefficients of active enzyme solutions can be determined with Pulsed Field Gradient Nuclear Magnetic Resonance (PFG-NMR). The advantage of PFG-NMR is that the motion of the molecule of interest is directly observed in its native state without the need for any labelling. Furthermore, PFG-NMR is model-free and thus yields absolute diffusion constants. Our PFG-NMR experiments of solutions containing active fructose-bisphosphate aldolase from rabbit muscle do not show any diffusion enhancement for the active enzymes, nor the surrounding molecules. Additionally, we do not observe any diffusion enhancement of aldolase in the presence of its inhibitor pyrophosphate.
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Affiliation(s)
- Jan-Philipp Günther
- Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569 Stuttgart, Germany
| | - Günter Majer
- Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569 Stuttgart, Germany
| | - Peer Fischer
- Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569 Stuttgart, Germany
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Bastos-Arrieta J, Bauer C, Eychmüller A, Simmchen J. Galvanic replacement induced electromotive force to propel Janus micromotors. J Chem Phys 2019; 150:144902. [PMID: 30981224 DOI: 10.1063/1.5085838] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Electrochemistry is a highly versatile part of chemical research which is involved in many of the processes in the field of micromotion. Its input has been crucial from the synthesis of microstructures to the explanation of phoretic mechanisms. However, using electrochemical effects to propel artificial micromotors is still to be achieved. Here, we show that the forces generated by electrochemical reactions can not only create active motion, but they are also strong enough to overcome the adhesion to the substrate, caused by the increased ionic strength of the solutions containing the ions of more noble metals themselves. The galvanic replacement of copper by platinum ions is a spontaneous process, which not only provides a sufficiently strong electromotive force to propel the Janus structures but also results in asymmetric Pt-hatted structures, which can be further used as catalytic micromotors.
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Affiliation(s)
| | - Christoph Bauer
- Physical Chemistry TU Dresden, Zellescher Weg 19, 01062 Dresden, Germany
| | | | - Juliane Simmchen
- Physical Chemistry TU Dresden, Zellescher Weg 19, 01062 Dresden, Germany
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Seki T, Okuzono T, Toyotama A, Yamanaka J. Mechanism of diffusiophoresis with chemical reaction on a colloidal particle. Phys Rev E 2019; 99:012608. [PMID: 30780366 DOI: 10.1103/physreve.99.012608] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Indexed: 11/07/2022]
Abstract
A mechanism for diffusiophoresis of a charged colloidal particle undergoing surface chemical reaction is proposed. A theoretical model is constructed to describe the dynamics of the particle and the surrounding solution of a weak electrolyte. Theoretical analysis and numerical simulations of the model reveal that phoretic motion of the particle emerges in response to a concentration gradient of electrolyte. The concentration gradient breaks the spherical symmetry of the surface charge distribution, which gives rise to a net force on the particle and leads to directional motion of the particle.
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Affiliation(s)
- Tomotaka Seki
- Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan
| | - Tohru Okuzono
- Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan
| | - Akiko Toyotama
- Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan
| | - Junpei Yamanaka
- Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan
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Xiao Z, Wei M, Wang W. A Review of Micromotors in Confinements: Pores, Channels, Grooves, Steps, Interfaces, Chains, and Swimming in the Bulk. ACS APPLIED MATERIALS & INTERFACES 2019; 11:6667-6684. [PMID: 30562451 DOI: 10.1021/acsami.8b13103] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
One of the recent frontiers of nanotechnology research involves machines that operate at nano- and microscales, also known as nano/micromotors. Their potential applications in biomedicine, environmental sciences and engineering, military and defense industries, self-assembly, and many other areas have fueled an intense interest in this topic over the last 15 years. Despite deepened understanding of their propulsion mechanisms, we are still in the early days of exploring the dynamics of micromotors in complex and more realistic environments. Confinements, as a typical example of complex environments, are extremely relevant to the applications of micromotors, which are expected to travel in mucus gels, blood vessels, reproductive and digestive tracts, microfluidic chips, and capillary tubes. In this review, we summarize and critically examine recent studies (mostly experimental ones) of micromotor dynamics in confinements in 3D (spheres and porous network, channels, grooves, steps, and obstacles), 2D (liquid-liquid, liquid-solid, and liquid-air interfaces), and 1D (chains). In addition, studies of micromotors moving in the bulk solution and the usefulness of acoustic levitation is discussed. At the end of this article, we summarize how confinements can affect micromotors and offer our insights on future research directions. This review article is relevant to readers who are interested in the interactions of materials with interfaces and structures at the microscale and helpful for the design of smart and multifunctional materials for various applications.
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Affiliation(s)
- Zuyao Xiao
- School of Materials Science and Engineering , Harbin Institute of Technology (Shenzhen) , Shenzhen , Guangdong 518055 , China
| | - Mengshi Wei
- School of Materials Science and Engineering , Harbin Institute of Technology (Shenzhen) , Shenzhen , Guangdong 518055 , China
| | - Wei Wang
- School of Materials Science and Engineering , Harbin Institute of Technology (Shenzhen) , Shenzhen , Guangdong 518055 , China
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Shape-directed rotation of homogeneous micromotors via catalytic self-electrophoresis. Nat Commun 2019; 10:495. [PMID: 30700714 PMCID: PMC6353883 DOI: 10.1038/s41467-019-08423-7] [Citation(s) in RCA: 76] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2018] [Accepted: 01/07/2019] [Indexed: 11/17/2022] Open
Abstract
The pursuit of chemically-powered colloidal machines requires individual components that perform different motions within a common environment. Such motions can be tailored by controlling the shape and/or composition of catalytic microparticles; however, the ability to design particle motions remains limited by incomplete understanding of the relevant propulsion mechanism(s). Here, we demonstrate that platinum microparticles move spontaneously in solutions of hydrogen peroxide and that their motions can be rationally designed by controlling particle shape. Nanofabricated particles with n-fold rotational symmetry rotate steadily with speed and direction specified by the type and extent of shape asymmetry. The observed relationships between particle shape and motion provide evidence for a self-electrophoretic propulsion mechanism, whereby anodic oxidation and cathodic reduction occur at different rates at different locations on the particle surface. We develop a mathematical model that explains how particle shape impacts the relevant electrocatalytic reactions and the resulting electrokinetic flows that drive particle motion. Self-propelled motors operating at the micro- or nanoscale can be powered by catalytic reactions and show appealing potential in robotic applications. Brooks et al. describe how the motions of platinum spinners in hydrogen peroxide solutions can be rationally designed by controlling particle shape.
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Warren PB, Shin S, Stone HA. Diffusiophoresis in ionic surfactants: effect of micelle formation. SOFT MATTER 2019; 15:278-288. [PMID: 30534797 DOI: 10.1039/c8sm01472h] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We explore the consequences of micelle formation for diffusiophoresis of charged colloidal particles in ionic surfactant concentration gradients, using a quasi-chemical association model for surfactant self assembly. The electrophoretic contribution to diffusiophoresis is determined by re-arranging the Nernst-Planck equations, and the chemiphoretic contribution is estimated by making plausible approximations for the density profiles in the electrical double layer surrounding the particle. For sub-micellar solutions we find that a particle will typically be propelled down the concentration gradient, although electrophoresis and chemiphoresis are finely balanced and the effect is sensitive to the detailed parameter choices and simplifying assumptions in the model. Above the critical micelle concentration (CMC), diffusiophoresis becomes much weaker and may even reverse sign, due to the fact that added surfactant goes into building micelles and not augmenting the monomer or counterion concentrations. We present detailed calculations for sodium dodecyl sulfate (SDS), finding that the typical drift speed for a colloidal particle in a ∼100 μm length scale SDS gradient is ∼1 μm s-1 below the CMC, falling to ⪅0.2 μm s-1 above the CMC. These predictions are broadly in agreement with recent experimental work.
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Affiliation(s)
- Patrick B Warren
- Unilever R&D Port Sunlight, Quarry Road East, Bebington, Wirral, CH63 3JW, UK.
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