1
|
Nizkaya TV, Asmolov ES, Vinogradova OI. Theoretical modeling of catalytic self-propulsion. Curr Opin Colloid Interface Sci 2022. [DOI: 10.1016/j.cocis.2022.101637] [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]
|
2
|
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.
Collapse
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
| |
Collapse
|
3
|
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.
Collapse
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
| |
Collapse
|
4
|
Martínez-Pedrero F. Static and dynamic behavior of magnetic particles at fluid interfaces. Adv Colloid Interface Sci 2020; 284:102233. [PMID: 32961419 DOI: 10.1016/j.cis.2020.102233] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Revised: 08/04/2020] [Accepted: 08/05/2020] [Indexed: 10/23/2022]
Abstract
This perspective work reviews the current status of research on magnetic particles at fluid interfaces. The article gives both a unified overview of recent experimental advances and theoretical studies centered on very different phenomena that share a common characteristic: they involve adsorbed magnetic particles that range in size from a few nanometers to several millimeters. Because of their capability of being remotely piloted through controllable external fields, magnetic particles have proven essential as building blocks in the design of new techniques, smart materials and micromachines, with new tunable properties and prospective applications in engineering and biotechnology. Once adsorbed at a fluid-fluid interfase, in a process that can be facilitated via the application of magnetic field gradients, these particles often result sorely confined to two dimensions (2D). In this configuration, inter-particle forces directed along the perpendicular to the interface are typically very small compared to the surface forces. Hence, the confinement and symmetry breaking introduced by the presence of the surface play an important role on the response of the system to the application of an external field. In monolayers of particles where the magnetic is predominant interaction, the states reached are strongly determined by the mode and orientation of the applied field, which promote different patterns and processes. Furthermore, they can reproduce some of the dynamic assemblies displayed in bulk or form new ones, that take advantage of the interfacial phenomena or of the symmetry breaking introduce by the confining boundary. Magnetic colloids are also widely used for unraveling the guiding principles of 2D dynamic self-assembly, in designs devised for producing interface transport, as tiny probes for assessing interfacial rheological properties, neglecting the bulk and inertia contributions, as well as actuated stabilizing agents in foams and emulsions.
Collapse
|
5
|
Martin RW, Zwanikken JW. Controlling the structure and mixing properties of anisotropic active particles with the direction of self-propulsion. SOFT MATTER 2019; 15:7757-7764. [PMID: 31482905 DOI: 10.1039/c9sm01120j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
In the search for advanced materials active particles could offer unique structural and functional properties, with tunable time-dependent characteristics. We demonstrate here that the direction of self-propulsion, relative to the particle orientation, may be as influential for the phase behavior as the pair interactions are for passive particles, and enable dynamic properties that are not available to passive systems. We perform simulations on ensembles of self-propelled squares, and find that squares that self-propel in the direction perpendicular to a side rapidly reach a steady state with a characteristic cluster distribution, positional order, and well-defined diffusion constant. After tuning the direction towards a corner, the particles form large and dense clusters that show a transient collective motion, and display remarkable fluctuations over long time scales, with a distinct periodicity. Clusters of these particles appear unstable beyond a critical size, and susceptible to a catastrophic disintegration. Directionality is found to effect equally sharp transitions in the mixing properties of active squares and passive squares, and the behavior of the passive ensemble. We relate directionality to the collision dynamics and the resulting reaction network of clusters, evolved by a Kinetic Monte Carlo algorithm, to correlate propulsion direction to the observed phase behavior. Understanding this behavior could offer new design rules for programmable materials, and grant further insights in the dynamic processes that nature employs for self-assembly.
Collapse
Affiliation(s)
- Robert W Martin
- Department of Physics and Applied Physics, University of Massachusetts, Lowell, USA.
| | | |
Collapse
|
6
|
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.
Collapse
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.
| | | |
Collapse
|
7
|
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.
Collapse
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.
| |
Collapse
|
8
|
Abstract
Despite mounting evidence that the same gradients, which active colloids use for swimming, induce important cross-interactions (phoretic interactions), they are still ignored in most many-body descriptions, perhaps to avoid complexity and a zoo of unknown parameters. Here we derive a simple model, which reduces phoretic far-field interactions to a pair-interaction whose strength is mainly controlled by one genuine parameter (swimming speed). The model suggests that phoretic interactions are generically important for autophoretic colloids (unless effective screening of the phoretic fields is strong) and should dominate over hydrodynamic interactions for the typical case of half-coating and moderately nonuniform surface mobilities. Unlike standard minimal models, but in accordance with canonical experiments, our model generically predicts dynamic clustering in active colloids at a low density. This suggests that dynamic clustering can emerge from the interplay of screened phoretic attractions and active diffusion.
Collapse
Affiliation(s)
- Benno Liebchen
- Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany
| | - Hartmut Löwen
- Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany
| |
Collapse
|
9
|
Ellis E, Moorthy S, Chio WIK, Lee TC. Artificial molecular and nanostructures for advanced nanomachinery. Chem Commun (Camb) 2018; 54:4075-4090. [PMID: 29484317 DOI: 10.1039/c7cc09133h] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Artificial nanomachines can be broadly defined as manmade molecular and nanosystems that are capable of performing useful tasks, very often, by means of doing mechanical work at the nanoscale. Recent advances in nanoscience allow these tiny machines to be designed and made with unprecedented sophistication and complexity, showing promise in novel applications, including molecular assemblers, self-propelling nanocarriers and in vivo molecular computation. This Feature Article overviews and compares major types of nanoscale machines, including molecular machines, self-assembled nanomachines and hybrid inorganic nanomachines, to reveal common structural features and operating principles across different length scales and material systems. We will focus on systems with feature size between 1 and 100 nm, where classical laws of physics meet those of quantum mechanics, giving rise to a spectrum of exotic physiochemical properties. Concepts of nanomachines will be illustrated by selected seminal work along with state-of-the-art progress, including our own contribution, across the fields. The Article will conclude with a brief outlook of this exciting research area.
Collapse
Affiliation(s)
- Elizabeth Ellis
- Department of Chemistry, University College London (UCL), UK and Institute for Materials Research and Engineering (IMRE), Agency for Science Technology and Research (A*STAR), Singapore
| | - Suresh Moorthy
- Department of Chemistry, University College London (UCL), UK and Institute for Materials Discovery, University College London (UCL), UK.
| | - Weng-I Katherine Chio
- Department of Chemistry, University College London (UCL), UK and Singapore Bioimaging Consortium (SBIC), Agency for Science Technology and Research (A*STAR), Singapore
| | - Tung-Chun Lee
- Department of Chemistry, University College London (UCL), UK and Institute for Materials Discovery, University College London (UCL), UK.
| |
Collapse
|
10
|
Shen T, Vernerey F. Phoretic motion of soft vesicles and droplets: an XFEM/particle-based numerical solution. COMPUTATIONAL MECHANICS 2017; 60:143-161. [PMID: 29200544 PMCID: PMC5708599 DOI: 10.1007/s00466-017-1399-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Accepted: 03/05/2017] [Indexed: 06/07/2023]
Abstract
When immersed in solution, surface-active particles interact with solute molecules and migrate along gradients of solute concentration. Depending on the conditions, this phenomenon could arise from either diffusiophoresis or the Marangoni effect, both of which involve strong interactions between the fluid and the particle surface. We introduce here a numerical approach that can accurately capture these interactions, and thus provide an efficient tool to understand and characterize the phoresis of soft particles. The model is based on a combination of the extended finite element-that enable the consideration of various discontinuities across the particle surface-and the particle-based moving interface method-that is used to measure and update the interface deformation in time. In addition to validating the approach with analytical solutions, the model is used to study the motion of deformable vesicles in solutions with spatial variations in both solute concentration and temperature.
Collapse
Affiliation(s)
- Tong Shen
- Mechanical Engineering, University of Colorado Boulder, 1111 Engineering Drive, Boulder, CO 80309-0427, USA
| | - Franck Vernerey
- Mechanical Engineering, University of Colorado Boulder, 1111 Engineering Drive, Boulder, CO 80309-0427, USA
| |
Collapse
|
11
|
Fortini A, Sear RP. Stratification and Size Segregation of Ternary and Polydisperse Colloidal Suspensions during Drying. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:4796-4805. [PMID: 28423894 DOI: 10.1021/acs.langmuir.7b00946] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We investigate the drying process of three-component and polydisperse colloidal suspensions using Brownian dynamics simulations. We have previously reported (Phys. Rev. Lett. 2016, 116, 118301) on the drying of binary mixtures. For binary mixtures, we found that a gradient of colloidal osmotic pressure develops during drying and that this leads to the final film being stratified with a layer of smaller particles on top of a layer of larger particles. Here, we find that stratification by size is very general and also occurs in ternary and polydisperse mixtures. We name the segregation effect colloidal diffusiophoresis. In particular, we show that by changing the composition of a ternary mixture, different stratification morphologies can be achieved and hence the film properties can be tuned. In polydisperse spheres, colloidal diffusiophoresis leads to enrichment in the large particles at the bottom part of the film, whereas the top part is enriched with smaller particles. This segregation means that in the final film, the particle size distribution depends on height. Thus, the properties of the film will then depend on height. We propose a model that predicts a power-law dependence of the phoretic velocity on particle size. Results from the model and simulation show a good agreement.
Collapse
Affiliation(s)
- Andrea Fortini
- Department of Physics, University of Surrey , Guildford GU2 7XH, United Kingdom
| | - Richard P Sear
- Department of Physics, University of Surrey , Guildford GU2 7XH, United Kingdom
| |
Collapse
|
12
|
Zhang J, Zheng X, Cui H, Silber-Li Z. The Self-Propulsion of the Spherical Pt–SiO2 Janus Micro-Motor. MICROMACHINES 2017. [PMCID: PMC6189969 DOI: 10.3390/mi8040123] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The double-faced Janus micro-motor, which utilizes the heterogeneity between its two hemispheres to generate self-propulsion, has shown great potential in water cleaning, drug delivery in micro/nanofluidics, and provision of power for a novel micro-robot. In this paper, we focus on the self-propulsion of a platinum–silica (Pt–SiO2) spherical Janus micro-motor (JM), which is one of the simplest micro-motors, suspended in a hydrogen peroxide solution (H2O2). Due to the catalytic decomposition of H2O2 on the Pt side, the JM is propelled by the established concentration gradient known as diffusoiphoretic motion. Furthermore, as the JM size increases to O (10 μm), oxygen molecules nucleate on the Pt surface, forming microbubbles. In this case, a fast bubble propulsion is realized by the microbubble cavitation-induced jet flow. We systematically review the results of the above two distinct mechanisms: self-diffusiophoresis and microbubble propulsion. Their typical behaviors are demonstrated, based mainly on experimental observations. The theoretical description and the numerical approach are also introduced. We show that this tiny motor, though it has a very simple structure, relies on sophisticated physical principles and can be used to fulfill many novel functions.
Collapse
Affiliation(s)
- Jing Zhang
- School of Environment and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China; (J.Z.); (H.C.)
| | - Xu Zheng
- State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China;
- Correspondence: ; Tel.: +86-10-8254-3925
| | - Haihang Cui
- School of Environment and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China; (J.Z.); (H.C.)
| | - Zhanhua Silber-Li
- State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China;
| |
Collapse
|
13
|
Niu R, Kreissl P, Brown AT, Rempfer G, Botin D, Holm C, Palberg T, de Graaf J. Microfluidic pumping by micromolar salt concentrations. SOFT MATTER 2017; 13:1505-1518. [PMID: 28127614 DOI: 10.1039/c6sm02240e] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
An ion-exchange-resin-based microfluidic pump is introduced that utilizes trace amounts of ions to generate fluid flows. We show experimentally that our pump operates in almost deionized water for periods exceeding 24 h and induces fluid flows of μm s-1 over hundreds of μm. This flow displays a far-field, power-law decay which is characteristic of two-dimensional (2D) flow when the system is strongly confined and of three-dimensional (3D) flow when it is not. Using theory and numerical calculations we demonstrate that our observations are consistent with electroosmotic pumping driven by μmol L-1 ion concentrations in the sample cell that serve as 'fuel' to the pump. Our study thus reveals that trace amounts of charge carriers can produce surprisingly strong fluid flows; an insight that should benefit the design of a new class of microfluidic pumps that operate at very low fuel concentrations.
Collapse
Affiliation(s)
- Ran Niu
- Institut für Physik, Johannes Gutenberg Universität Mainz, 55128 Mainz, Germany
| | - Patrick Kreissl
- Institute for Computational Physics, Universität Stuttgart, Allmandring 3, 70569 Stuttgart, Germany
| | - Aidan T Brown
- SUPA, School of Physics and Astronomy, University of Edinburgh, JCMB Kings Buildings, Edinburgh EH9 3FD, UK.
| | - Georg Rempfer
- Institute for Computational Physics, Universität Stuttgart, Allmandring 3, 70569 Stuttgart, Germany
| | - Denis Botin
- Institut für Physik, Johannes Gutenberg Universität Mainz, 55128 Mainz, Germany
| | - Christian Holm
- Institute for Computational Physics, Universität Stuttgart, Allmandring 3, 70569 Stuttgart, Germany
| | - Thomas Palberg
- Institut für Physik, Johannes Gutenberg Universität Mainz, 55128 Mainz, Germany
| | - Joost de Graaf
- SUPA, School of Physics and Astronomy, University of Edinburgh, JCMB Kings Buildings, Edinburgh EH9 3FD, UK.
| |
Collapse
|
14
|
Brown AT, Poon WCK, Holm C, de Graaf J. Ionic screening and dissociation are crucial for understanding chemical self-propulsion in polar solvents. SOFT MATTER 2017; 13:1200-1222. [PMID: 28098324 DOI: 10.1039/c6sm01867j] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Polar solvents like water support the bulk dissociation of themselves and their solutes into ions, and the re-association of these ions into neutral molecules in a dynamic equilibrium, e.g., H2O2 ⇌ H+ + HO2-. Using continuum theory, we study the influence of these association-dissociation reactions on the self-propulsion of colloids driven by surface chemical reactions (chemical swimmers). We find that association-dissociation reactions should have a strong influence on swimmers' behaviour, and therefore should be included in future modelling. In particular, such bulk reactions should permit charged swimmers to propel electrophoretically even if all species involved in the surface reactions are neutral. The bulk reactions also significantly modify the predicted speed of chemical swimmers propelled by ionic currents, by up to an order of magnitude. For swimmers whose surface reactions produce both anions and cations (ionic self-diffusiophoresis), the bulk reactions produce an additional reactive screening length, analogous to the Debye length in electrostatics. This in turn leads to an inverse relationship between swimmer radius and swimming speed, which could provide an alternative explanation for recent experimental observations on Pt-polystyrene Janus swimmers [S. Ebbens et al., Phys. Rev. E: Stat., Nonlinear, Soft Matter Phys., 2012, 85, 020401]. We also use our continuum theory to investigate the effect of the Debye screening length itself, going beyond the infinitely-thin-screening-length approximation used by previous analytical theories. We identify significant departures from this limiting behaviour for micron-sized swimmers under typical experimental conditions and find that the approximation fails entirely for nanoscale swimmers.
Collapse
Affiliation(s)
- Aidan T Brown
- SUPA, School of Physics and Astronomy, The University of Edinburgh, King's Buildings, Peter Guthrie Tait Road, Edinburgh, EH9 3FD, UK.
| | - Wilson C K Poon
- SUPA, School of Physics and Astronomy, The University of Edinburgh, King's Buildings, Peter Guthrie Tait Road, Edinburgh, EH9 3FD, UK.
| | - Christian Holm
- Institute for Computational Physics, Stuttgart University, Pfaffenwaldring 27, D-70569 Stuttgart, Germany
| | - Joost de Graaf
- SUPA, School of Physics and Astronomy, The University of Edinburgh, King's Buildings, Peter Guthrie Tait Road, Edinburgh, EH9 3FD, UK. and Institute for Computational Physics, Stuttgart University, Pfaffenwaldring 27, D-70569 Stuttgart, Germany
| |
Collapse
|
15
|
Kuron M, Rempfer G, Schornbaum F, Bauer M, Godenschwager C, Holm C, de Graaf J. Moving charged particles in lattice Boltzmann-based electrokinetics. J Chem Phys 2016; 145:214102. [DOI: 10.1063/1.4968596] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Michael Kuron
- Institut für Computerphysik, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Georg Rempfer
- Institut für Computerphysik, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Florian Schornbaum
- Lehrstuhl für Systemsimulation, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Martin Bauer
- Lehrstuhl für Systemsimulation, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Christian Godenschwager
- Lehrstuhl für Systemsimulation, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Christian Holm
- Institut für Computerphysik, Universität Stuttgart, 70550 Stuttgart, Germany
| | - Joost de Graaf
- Institut für Computerphysik, Universität Stuttgart, 70550 Stuttgart, Germany
| |
Collapse
|
16
|
Rempfer G, Ehrhardt S, Holm C, de Graaf J. Nanoparticle Translocation through Conical Nanopores: A Finite Element Study of Electrokinetic Transport. MACROMOL THEOR SIMUL 2016. [DOI: 10.1002/mats.201600051] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Georg Rempfer
- Institute for Computational Physics (ICP); University of Stuttgart; Allmandring 3 70569 Stuttgart Germany
| | - Sascha Ehrhardt
- Institute for Computational Physics (ICP); University of Stuttgart; Allmandring 3 70569 Stuttgart Germany
| | - Christian Holm
- Institute for Computational Physics (ICP); University of Stuttgart; Allmandring 3 70569 Stuttgart Germany
| | - Joost de Graaf
- Institute for Computational Physics (ICP); University of Stuttgart; Allmandring 3 70569 Stuttgart Germany
| |
Collapse
|
17
|
Rempfer G, Davies GB, Holm C, de Graaf J. Reducing spurious flow in simulations of electrokinetic phenomena. J Chem Phys 2016; 145:044901. [DOI: 10.1063/1.4958950] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Georg Rempfer
- Institute for Computational Physics (ICP), University of Stuttgart, Allmandring 3, 70569 Stuttgart, Germany
| | - Gary B. Davies
- Institute for Computational Physics (ICP), University of Stuttgart, Allmandring 3, 70569 Stuttgart, Germany
| | - Christian Holm
- Institute for Computational Physics (ICP), University of Stuttgart, Allmandring 3, 70569 Stuttgart, Germany
| | - Joost de Graaf
- School of Physics and Astronomy, University of Edinburgh, Scotland, Edinburgh EH9 3JL, United Kingdom
| |
Collapse
|