51
|
Marbach S, Bocquet L. Osmosis, from molecular insights to large-scale applications. Chem Soc Rev 2019; 48:3102-3144. [PMID: 31114820 DOI: 10.1039/c8cs00420j] [Citation(s) in RCA: 107] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Osmosis is a universal phenomenon occurring in a broad variety of processes and fields. It is the archetype of entropic forces, both trivial in its fundamental expression - the van 't Hoff perfect gas law - and highly subtle in its physical roots. While osmosis is intimately linked with transport across membranes, it also manifests itself as an interfacial transport phenomenon: the so-called diffusio-osmosis and -phoresis, whose consequences are presently actively explored for example for the manipulation of colloidal suspensions or the development of active colloidal swimmers. Here we give a global and unifying view of the phenomenon of osmosis and its consequences with a multi-disciplinary perspective. Pushing the fundamental understanding of osmosis allows one to propose new perspectives for different fields and we highlight a number of examples along these lines, for example introducing the concepts of osmotic diodes, active separation and far from equilibrium osmosis, raising in turn fundamental questions in the thermodynamics of separation. The applications of osmosis are also obviously considerable and span very diverse fields. Here we discuss a selection of phenomena and applications where osmosis shows great promises: osmotic phenomena in membrane science (with recent developments in separation, desalination, reverse osmosis for water purification thanks in particular to the emergence of new nanomaterials); applications in biology and health (in particular discussing the kidney filtration process); osmosis and energy harvesting (in particular, osmotic power and blue energy as well as capacitive mixing); applications in detergency and cleaning, as well as for oil recovery in porous media.
Collapse
Affiliation(s)
- Sophie Marbach
- Laboratoire de Physique de l'Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris-Diderot, Sorbonne Paris Cité, Paris, France.
| | | |
Collapse
|
52
|
Jalilvand Z, Pawar AB, Kretzschmar I. Experimental Study of the Motion of Patchy Particle Swimmers Near a Wall. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:15593-15599. [PMID: 30403351 DOI: 10.1021/acs.langmuir.8b03220] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
In this work, we demonstrate our ability to precisely tailor the surface activity of self-propelled active colloids by varying the size of the active area. The quasi two-dimensional autonomous motion of spherical patchy particle swimmers is studied in a chemical environment in the vicinity of a solid boundary. Oxidative decomposition of hydrogen peroxide into oxygen and water occurs only on a well-defined Pt-coated section of the polystyrene particle surface. The asymmetric distribution of product molecules interacting with the particle leads to the autonomous motion, which is characterized as the patch size varies from 11 to 25 to 50% of the particle surface area. The phoretic motion of patchy particle swimmers is analytically predicted by a model developed by Popescu et al. and shows good agreement with the experimentally observed velocities when the influence of the wall on the preferential rotational motion of the particles near the solid boundary is considered. The study illustrates the potential to precisely engineer the motion of particles by controlling their properties rather than depending on changes in the environment.
Collapse
Affiliation(s)
- Zohreh Jalilvand
- Department of Chemical Engineering , City College of the City University of New York (CUNY) , 140th Street & Convent Avenue , New York , New York 10031 , United States
| | - Amar B Pawar
- Department of Chemical Engineering , City College of the City University of New York (CUNY) , 140th Street & Convent Avenue , New York , New York 10031 , United States
| | - Ilona Kretzschmar
- Department of Chemical Engineering , City College of the City University of New York (CUNY) , 140th Street & Convent Avenue , New York , New York 10031 , United States
| |
Collapse
|
53
|
Kuron M, Kreissl P, Holm C. Toward Understanding of Self-Electrophoretic Propulsion under Realistic Conditions: From Bulk Reactions to Confinement Effects. Acc Chem Res 2018; 51:2998-3005. [PMID: 30417644 DOI: 10.1021/acs.accounts.8b00285] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Active matter concerns itself with the study of particles that convert energy into work, typically motion of the particle itself. This field saw a surge of interest over the past decade, after the first micrometer-sized, man-made chemical motors were created. These particles served as a simple model system for studying in a well-controlled manner complex motion and cooperative behavior as known from biology. In addition, they have stimulated new efforts in understanding out-of-equilibrium statistical physics and started a revolution in microtechnology and robotics. Concentrated effort has gone into realizing these ambitions, and yet much remains unknown about the chemical motors themselves. The original designs for self-propelled particles relied on the conversion of the chemical energy of hydrogen peroxide into motion via catalytic decomposition taking place heterogeneously over the surface of the motor. This sets up gradients of chemical fields around the particle, which allow it to autophorese. That is, the interaction between the motor and the heterogeneously distributed solute species can drive fluid flow and the motor itself. There are two basic designs: the first relies on redox reactions taking place between the two sides of a bimetal, for example, a gold-platinum Janus sphere or nanorod. The second uses a catalytic layer of platinum inhomogeneously vapor-deposited onto a nonreactive particle. For convenience's sake, these can be referred to as redox motors and monometallic half-coated motors, respectively. To date, most researchers continue to rely on variations of these simple, yet elegant designs for their experiments. However, there is ongoing debate on the exact way chemical energy is transduced into motion in these motors. Many of the experimental observations on redox motors were successfully modeled via self-electrophoresis, while for half-coated motors there has been a strong focus on self-diffusiophoresis. Currently, there is mounting evidence that self-electrophoresis provides the dominant contribution to the observed speeds of half-coated motors, even if the vast majority of the reaction products are electroneutral. In this Account, we will summarize the most common electrophoretic propulsion model and discuss its strengths and weaknesses in relation to recent experiments. We will comment on the possible need to go beyond surface reactions and consider the entire medium as an "active fluid" that can create and annihilate charged species. This, together with confinement and collective effects, makes it difficult to gain a detailed understanding of these swimmers. The potentially dominant effect of confinement is highlighted on the basis of a recent study of an electro-osmotic pump that drives fluid along a substrate. Detailed analysis of this system allows for identification of the electro-osmotic driving mechanism, which is powered by micromolar salt concentrations. We will discuss how our latest numerical solver developments, based on the lattice Boltzmann method, should enable us to study collective behavior in systems comprised of these and other electrochemical motors in realistic environments. We conclude with an outlook on the future of modeling chemical motors that may facilitate the community's microtechnological ambitions.
Collapse
Affiliation(s)
- Michael Kuron
- Institute for Computational Physics (ICP), University of Stuttgart, Allmandring 3, 70569 Stuttgart, Germany
| | - Patrick Kreissl
- 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
| |
Collapse
|
54
|
Popescu MN, Uspal WE, Domínguez A, Dietrich S. Effective Interactions between Chemically Active Colloids and Interfaces. Acc Chem Res 2018; 51:2991-2997. [PMID: 30403132 DOI: 10.1021/acs.accounts.8b00237] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Chemically active colloids can achieve force- and torque-free motility ("self-propulsion") via the promotion, on their surface, of catalytic chemical reactions involving the surrounding solution. Such systems are valuable both from a theoretical perspective, serving as paradigms for nonequilibrium processes, as well as from an application viewpoint, according to which active colloids are envisioned to play the role of carriers ("engines") in novel lab-on-a-chip devices. The motion of such colloids is intrinsically connected with a "chemical field", i.e., the distribution near the colloid of the number densities of the various chemical species present in the solution, and with the hydrodynamic flow of the solution around the particle. In most of the envisioned applications, and in virtually all reported experimental studies, the active colloids operate under spatial confinement (e.g., within a microfluidic channel, a drop, a free-standing liquid film, etc.). In such cases, the chemical field and the hydrodynamic flow associated with an active colloid are influenced by any nearby confining surfaces, and these disturbances couple back to the particle. Thus, an effective interaction with the spatial confinement arises. Consequently, the particle is endowed with means to perceive and to respond to its environment. Understanding these effective interactions, finding the key parameters which control them, and designing particles with desired, preconfigured responses to given environments, require interdisciplinary approaches which synergistically integrate methods and knowledge from physics, chemistry, engineering, and materials science. Here we review how, via simple models of chemical activity and self-phoretic motion, progress has recently been made in understanding the basic physical principles behind the complex behaviors exhibited by active particles near interfaces. First, we consider the occurrence of "interface-bounded" steady states of chemically active colloids near simple, nonresponsive interfaces. Examples include particles "sliding" along, or "hovering" above, a hard planar wall while inducing hydrodynamic flow of the solution. These states lay the foundations for concepts like the guidance of particles by the topography of the wall. We continue to discuss responsive interfaces: a suitable chemical patterning of a planar wall allows one to bring the particles into states of motion which are spatially localized (e.g., within chemical stripes or along chemical steps). These occur due to the wall responding to the activity-induced chemical gradients by generating osmotic flows, which encode the surface-chemistry of the wall. Finally, we discuss how, via activity-induced Marangoni stresses, long-ranged effective interactions emerge from the strong hydrodynamic response of fluid interfaces. These examples highlight how in this context a desired behavior can be potentially selected by tuning suitable parameters (e.g., the phoretic mobility of the particle, or the strength of the Marangoni stress at an interface). This can be accomplished via a judicious design of the surface chemistry of the particle and of the boundary, or by the choice of the chemical reaction in solution.
Collapse
Affiliation(s)
- Mihail N. Popescu
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569 Stuttgart, Germany
- 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
- IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany
| | - Alvaro Domínguez
- Física Teórica, Universidad de Sevilla, Apdo. 1065, 41080 Sevilla, Spain
| | - Siegfried Dietrich
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569 Stuttgart, Germany
- IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany
| |
Collapse
|
55
|
Abstract
The ability to navigate in chemical gradients, called chemotaxis, is crucial for the survival of microorganisms. It allows them to find food and to escape from toxins. Many microorganisms can produce the chemicals to which they respond themselves and use chemotaxis for signaling, which can be seen as a basic form of communication, allowing ensembles of microorganisms to coordinate their behavior, for example, during embryogenesis, biofilm formation, or cellular aggregation. For example, Dictyostelium cells use signaling as a survival strategy: when starving, they produce certain chemicals toward which other cells show taxis. This leads to aggregation of the cells resulting in a multicellular aggregate that can sustain long starvation periods. Remarkably, the past decade has led to the development of synthetic microswimmers, which can self-propel through a solvent, analogously to bacteria and other microorganisms. The mechanism underlying the self-propulsion of synthetic microswimmers like camphor boats, droplet swimmers, and in particular autophoretic Janus colloids involves the production of certain chemicals. As we will discuss in this Account, the same chemicals (phoretic fields) involved in the self-propulsion of a (Janus) microswimmer also act on other ones and bias their swimming direction toward (or away from) the producing microswimmer. Synthetic microswimmers therefore provide a synthetic analogue to motile microorganisms interacting by taxis toward (or away from) self-produced chemical fields. In this Account, we review recent progress in the theoretical description of synthetic chemotaxis mainly based on simulations and field theoretical descriptions. We will begin with single motile particles leaving chemical trails behind with which they interact themselves, leading to effects like self-trapping or self-avoidance. Besides these self-interactions, in ensembles of synthetic motile particles each particle also responds to the chemicals produced by other particles, inducing chemical (or phoretic) cross-interactions. When these interactions are attractive, they commonly lead to clusters, even at low particle density. These clusters may either proceed toward macrophase separation, resembling Dictyostelium aggregation, or, as shown very recently, lead to dynamic clusters of self-limited size (dynamic clustering) as seen in experiments in autophoretic Janus colloids. Besides the classical case where chemical interactions are attractive, this Account discusses, as its main focus, repulsive chemical interactions, which can create a new and less known avenue to pattern formation in active systems leading to a variety of pattern, including clusters which are surrounded by shells of chemicals, traveling waves and more complex continuously reshaping patterns. In all these cases "synthetic signalling" can crucially determine the collective behavior of synthetic microswimmer ensembles and can be used as a design principle to create patterns in motile active particles.
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
|
56
|
Popescu MN, Uspal WE, Eskandari Z, Tasinkevych M, Dietrich S. Effective squirmer models for self-phoretic chemically active spherical colloids. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2018; 41:145. [PMID: 30569319 DOI: 10.1140/epje/i2018-11753-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 11/09/2018] [Indexed: 05/10/2023]
Abstract
Various aspects of self-motility of chemically active colloids in Newtonian fluids can be captured by simple models for their chemical activity plus a phoretic-slip hydrodynamic boundary condition on their surface. For particles of simple shapes (e.g., spheres) --as employed in many experimental studies-- which move at very low Reynolds numbers in an unbounded fluid, such models of chemically active particles effectively map onto the well studied so-called hydrodynamic squirmers (S. Michelin and E. Lauga, J. Fluid Mech. 747, 572 (2014)). Accordingly, intuitively appealing analogies of "pusher/puller/neutral" squirmers arise naturally. Within the framework of self-diffusiophoresis we illustrate the above-mentioned mapping and the corresponding flows in an unbounded fluid for a number of choices of the activity function (i.e., the spatial distribution and the type of chemical reactions across the surface of the particle). We use the central collision of two active particles as a simple, paradigmatic case for demonstrating that in the presence of other particles or boundaries the behavior of chemically active colloids may be qualitatively different, even in the far field, from the one exhibited by the corresponding "effective squirmer", obtained from the mapping in an unbounded fluid. This emphasizes that understanding the collective behavior and the dynamics under geometrical confinement of chemically active particles necessarily requires to explicitly account for the dependence of the hydrodynamic interactions on the distribution of chemical species resulting from the activity of the particles.
Collapse
Affiliation(s)
- M N Popescu
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569, Stuttgart, Germany.
- IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569, Stuttgart, Germany.
| | - W E Uspal
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569, Stuttgart, Germany
- IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569, Stuttgart, Germany
| | - Z Eskandari
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569, Stuttgart, Germany
- IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569, Stuttgart, Germany
| | - M Tasinkevych
- Centro de Física Teórica e Computacional, Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, P-1749-016, Lisboa, Portugal
| | - S Dietrich
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569, Stuttgart, Germany
- IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569, Stuttgart, Germany
| |
Collapse
|
57
|
Wang X, Baraban L, Nguyen A, Ge J, Misko VR, Tempere J, Nori F, Formanek P, Huang T, Cuniberti G, Fassbender J, Makarov D. High-Motility Visible Light-Driven Ag/AgCl Janus Micromotors. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2018; 14:e1803613. [PMID: 30369029 DOI: 10.1002/smll.201803613] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Indexed: 05/22/2023]
Abstract
Visible light-driven nano/micromotors are promising candidates for biomedical and environmental applications. This study demonstrates blue light-driven Ag/AgCl-based spherical Janus micromotors, which couple plasmonic light absorption with the photochemical decomposition of AgCl. These micromotors reveal high motility in pure water, i.e., mean squared displacements (MSD) reaching 800 µm2 within 8 s, which is 100× higher compared to previous visible light-driven Janus micromotors and 7× higher than reported ultraviolet (UV) light-driven AgCl micromotors. In addition to providing design rules to realize efficient Janus micromotors, the complex dynamics revealed by individual and assemblies of Janus motors is investigated experimentally and in simulations. The effect of suppressed rotational diffusion is focused on, compared to UV light-driven AgCl micromotors, as a reason for this remarkable increase of the MSD. Moreover, this study demonstrates the potential of using visible light-driven plasmonic Ag/AgCl-based Janus micromotors in human saliva, phosphate-buffered saline solution, the most common isotonic buffer that mimics the environment of human body fluids, and Rhodamine B solution, which is a typical polluted dye for demonstrations of photocatalytic environmental remediation. This new knowledge is useful for designing visible light driven nano/micromotors based on the surface plasmon resonance effect and their applications in assays relevant for biomedical and ecological sciences.
Collapse
Affiliation(s)
- Xu Wang
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Ion Beam Physics and Materials Research, Bautzner Landstrasse 400, 01328, Dresden, Germany
| | - Larysa Baraban
- Institute for Materials Science and Max Bergmann Center of Biomaterials, Technische Universität Dresden, 01062, Dresden, Germany
- Center for Advancing Electronics Dresden, Technische Universität Dresden, 01062, Dresden, Germany
| | - Anh Nguyen
- Institute for Materials Science and Max Bergmann Center of Biomaterials, Technische Universität Dresden, 01062, Dresden, Germany
| | - Jin Ge
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Ion Beam Physics and Materials Research, Bautzner Landstrasse 400, 01328, Dresden, Germany
| | - Vyacheslav R Misko
- Theory of Quantum and Complex Systems Laboratory, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen, Belgium
- Theoretical Quantum Physics Laboratory, RIKEN Cluster for Pioneering Research, Wako-shi, Saitama, 351-0198, Japan
| | - Jacques Tempere
- Theory of Quantum and Complex Systems Laboratory, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen, Belgium
- Lyman Laboratory of Physics, Harvard University, Cambridge, MA, 02138, USA
| | - Franco Nori
- Theory of Quantum and Complex Systems Laboratory, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen, Belgium
- Physics Department, University of Michigan, Ann Arbor, MI, 48109-1040, USA
| | - Petr Formanek
- Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Str. 6, 01069, Dresden, Germany
| | - Tao Huang
- Institute for Materials Science and Max Bergmann Center of Biomaterials, Technische Universität Dresden, 01062, Dresden, Germany
- Center for Advancing Electronics Dresden, Technische Universität Dresden, 01062, Dresden, Germany
| | - Gianaurelio Cuniberti
- Institute for Materials Science and Max Bergmann Center of Biomaterials, Technische Universität Dresden, 01062, Dresden, Germany
- Center for Advancing Electronics Dresden, Technische Universität Dresden, 01062, Dresden, Germany
| | - Jürgen Fassbender
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Ion Beam Physics and Materials Research, Bautzner Landstrasse 400, 01328, Dresden, Germany
| | - Denys Makarov
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Ion Beam Physics and Materials Research, Bautzner Landstrasse 400, 01328, Dresden, Germany
| |
Collapse
|
58
|
Domínguez A, Popescu MN. Phase coexistence in a monolayer of active particles induced by Marangoni flows. SOFT MATTER 2018; 14:8017-8029. [PMID: 30246847 DOI: 10.1039/c8sm00688a] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Thermally or chemically active colloids generate thermodynamic gradients in the solution in which they are immersed and thereby induce hydrodynamic flows that affect their dynamical evolution. Here we study a mean-field model for the many-body dynamics of a monolayer of spherically symmetric active particles located at a fluid-fluid interface. Due to the spherical symmetry, the particles do not self-propel. Instead, the dynamics is driven by the long-ranged Marangoni flows, due to the response of the interface to the activity of the particles, which compete with the direct interaction between particles. We demonstrate analytically that, in spite of the intrinsic out-of-equilibrium character of the system, the monolayer evolves to a "pseudoequilibrium" state, in which the Marangoni flows force the coexistence of the thermodynamic phases associated to the direct interaction. In particular, we study the most interesting case of a r-3 soft repulsion that models electrostatic or magnetic interparticle forces. For a sufficiently large average density, two-dimensional phase transitions (freezing from liquid to hexatic, and melting from solid to hexatic) should be observable in a radially stratified, "onion-like" structure within the monolayer. Furthermore, the analysis allows us to conclude that, while the activity may be too weak to allow direct detection of such induced Marangoni flows, it is relevant as a collective effect in the emergence of the experimentally observable spatial structure of phase coexistences noted above. Finally, the relevance of these results for potential experimental realizations is critically discussed.
Collapse
Affiliation(s)
- Alvaro Domínguez
- Física Teórica, Universidad de Sevilla, Apdo. 1065, E-41080 Sevilla, Spain.
| | | |
Collapse
|
59
|
Günther JP, Börsch M, Fischer P. Diffusion Measurements of Swimming Enzymes with Fluorescence Correlation Spectroscopy. Acc Chem Res 2018; 51:1911-1920. [PMID: 30160941 DOI: 10.1021/acs.accounts.8b00276] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Self-propelled chemical motors are chemically powered micro- or nanosized swimmers. The energy required for these motors' active motion derives from catalytic chemical reactions and the transformation of a fuel dissolved in the solution. While self-propulsion is now well established for larger particles, it is still unclear if enzymes, nature's nanometer-sized catalysts, are potentially also self-powered nanomotors. Because of its small size, any increase in an enzyme's diffusion due to active self-propulsion must be observed on top of the enzyme's passive Brownian motion, which dominates at this scale. Fluorescence correlation spectroscopy (FCS) is a sensitive method to quantify the diffusion properties of single fluorescently labeled molecules in solution. FCS experiments have shown a general increase in the diffusion constant of a number of enzymes when the enzyme is catalytically active. Diffusion enhancements after addition of the enzyme's substrate (and sometimes its inhibitor) of up to 80% have been reported, which is at least 1 order of magnitude higher than what theory would predict. However, many factors contribute to the FCS signal and in particular the shape of the autocorrelation function, which underlies diffusion measurements by fluorescence correlation spectroscopy. These effects need to be considered to establish if and by how much the catalytic activity changes an enzyme's diffusion. We carefully review phenomena that can play a role in FCS experiments and the determination of enzyme diffusion, including the dissociation of enzyme oligomers upon interaction with the substrate, surface binding of the enzyme to glass during the experiment, conformational changes upon binding, and quenching of the fluorophore. We show that these effects can cause changes in the FCS signal that behave similar to an increase in diffusion. However, in the case of the enzymes F1-ATPase and alkaline phosphatase, we demonstrate that there is no measurable increase in enzyme diffusion. Rather, dissociation and conformational changes account for the changes in the FCS signal in the former and fluorophore quenching in the latter. Within the experimental accuracy of our FCS measurements, we do not observe any change in diffusion due to activity for the enzymes we have investigated. We suggest useful control experiments and additional tests for future FCS experiments that should help establish if the observed diffusion enhancement is real or if it is due to an experimental or data analysis artifact. We show that fluorescence lifetime and mean intensity measurements are essential in order to identify the nature of the observed changes in the autocorrelation function. While it is clear from theory that chemically active enzymes should also act as self-propelled nanomotors, our FCS measurements show that the associated increase in diffusion is much smaller than previously reported. Further experiments are needed to quantify the contribution of the enzymes' catalytic activity to their self-propulsion. We hope that our findings help to establish a useful protocol for future FCS studies in this field and help establish by how much the diffusion of an enzyme is enhanced through catalytic activity.
Collapse
Affiliation(s)
- Jan-Philipp Günther
- Max Planck Institute for Intelligent Systems, 70569 Stuttgart, Germany
- Institute of Physical Chemistry, University of Stuttgart, 70569 Stuttgart, Germany
| | - Michael Börsch
- Jena University Hospital, Friedrich-Schiller University Jena, 07743 Jena, Germany
| | - Peer Fischer
- Max Planck Institute for Intelligent Systems, 70569 Stuttgart, Germany
- Institute of Physical Chemistry, University of Stuttgart, 70569 Stuttgart, Germany
| |
Collapse
|
60
|
Wang L, Popescu MN, Stavale F, Ali A, Gemming T, Simmchen J. Cu@TiO 2 Janus microswimmers with a versatile motion mechanism. SOFT MATTER 2018; 14:6969-6973. [PMID: 30074047 DOI: 10.1039/c8sm00808f] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We report novel metal-capped TiO2 photochemically-active colloids endowed with a 'hybrid drive': directional motion is achieved in water upon UV illumination, as well as in dilute peroxide solutions upon illumination with UV or visible light. From the different behaviours of nearby particles, we infer that distinct reaction pathways affect the local composition and flow of the solution.
Collapse
Affiliation(s)
- LinLin Wang
- Physical Chemistry TU Dresden, Zellescher Weg 19, 01062 Dresden, Germany.
| | | | | | | | | | | |
Collapse
|
61
|
Kurzthaler C, Devailly C, Arlt J, Franosch T, Poon WCK, Martinez VA, Brown AT. Probing the Spatiotemporal Dynamics of Catalytic Janus Particles with Single-Particle Tracking and Differential Dynamic Microscopy. PHYSICAL REVIEW LETTERS 2018; 121:078001. [PMID: 30169062 DOI: 10.1103/physrevlett.121.078001] [Citation(s) in RCA: 57] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2017] [Revised: 05/01/2018] [Indexed: 05/25/2023]
Abstract
We demonstrate differential dynamic microscopy and particle tracking for the characterization of the spatiotemporal behavior of active Janus colloids in terms of the intermediate scattering function (ISF). We provide an analytical solution for the ISF of the paradigmatic active Brownian particle model and find striking agreement with experimental results from the smallest length scales, where translational diffusion and self-propulsion dominate, up to the largest ones, which probe effective diffusion due to rotational Brownian motion. At intermediate length scales, characteristic oscillations resolve the crossover between directed motion to orientational relaxation and allow us to discriminate active Brownian motion from other reorientation processes, e.g., run-and-tumble motion. A direct comparison to theoretical predictions reliably yields the rotational and translational diffusion coefficients of the particles, the mean and width of their speed distribution, and the temporal evolution of these parameters.
Collapse
Affiliation(s)
- Christina Kurzthaler
- Institut für Theoretische Physik, Universität Innsbruck, Technikerstraße 21A, A-6020 Innsbruck, Austria
| | - Clémence Devailly
- School of Physics and Astronomy, University of Edinburgh, James Clerk Maxwell Building, Peter Guthrie Tait Road, Edinburgh EH9 3FD, United Kingdom
| | - Jochen Arlt
- School of Physics and Astronomy, University of Edinburgh, James Clerk Maxwell Building, Peter Guthrie Tait Road, Edinburgh EH9 3FD, United Kingdom
| | - Thomas Franosch
- Institut für Theoretische Physik, Universität Innsbruck, Technikerstraße 21A, A-6020 Innsbruck, Austria
| | - Wilson C K Poon
- School of Physics and Astronomy, University of Edinburgh, James Clerk Maxwell Building, Peter Guthrie Tait Road, Edinburgh EH9 3FD, United Kingdom
| | - Vincent A Martinez
- School of Physics and Astronomy, University of Edinburgh, James Clerk Maxwell Building, Peter Guthrie Tait Road, Edinburgh EH9 3FD, United Kingdom
| | - Aidan T Brown
- School of Physics and Astronomy, University of Edinburgh, James Clerk Maxwell Building, Peter Guthrie Tait Road, Edinburgh EH9 3FD, United Kingdom
| |
Collapse
|
62
|
Longbottom BW, Bon SAF. Improving the engine power of a catalytic Janus-sphere micromotor by roughening its surface. Sci Rep 2018; 8:4622. [PMID: 29545556 PMCID: PMC5854611 DOI: 10.1038/s41598-018-22917-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Accepted: 02/28/2018] [Indexed: 12/13/2022] Open
Abstract
Microspheres with catalytic caps have become a popular model system for studying self-propelled colloids. Existing experimental studies involve predominantly "smooth" particle surfaces. In this study we determine the effect of irregular surface deformations on the propulsive mechanism with a particular focus on speed. The particle surfaces of polymer microspheres were deformed prior to depositing a layer of platinum which resulted in the formation of nanoscopic pillars of catalyst. Self-propulsion was induced upon exposure of the micromotors to hydrogen peroxide, whilst they were dispersed in water. The topological surface features were shown to boost speed (~2×) when the underlying deformations are small (nanoscale), whilst large deformations afforded little difference despite a substantial apparent catalytic surface area. Colloids with deformed surfaces were more likely to display a mixture of rotational and translational propulsion than their "smooth" counterparts.
Collapse
Affiliation(s)
- Brooke W Longbottom
- Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, U.K
| | - Stefan A F Bon
- Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, U.K..
| |
Collapse
|
63
|
Zhou C, Zhang HP, Tang J, Wang W. Photochemically Powered AgCl Janus Micromotors as a Model System to Understand Ionic Self-Diffusiophoresis. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:3289-3295. [PMID: 29436833 DOI: 10.1021/acs.langmuir.7b04301] [Citation(s) in RCA: 83] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Micromotors are an emerging class of micromachines that could find potential applications in biomedicine, environmental remediation, and microscale self-assembly. Understanding their propulsion mechanisms holds the key to their future development. This is especially true for a popular category of micromotors that are driven by asymmetric surface photochemical reactions. Many of these micromotors release ionic species and are propelled via a mechanism termed "ionic self-diffusiophoresis". However, exactly how it operates remains vague. To address this fundamental yet important issue, we have developed a dielectric-AgCl Janus micromotor that clearly moves away from the AgCl side when exposed to UV or strong visible light. Taking advantage of numerical simulations and acoustic levitation techniques, we have provided tentative explanations for its speed decay over time as well as its directionality. In addition, photoactive AgCl micromotors demonstrate interesting gravitactic behaviors that hint at three-dimensional transport or sensing applications. The current work presents a well-controlled and easily fabricated model system to understand chemically powered micromotors, highlighting the usefulness of acoustic levitation for studying active matter free from the effect of boundaries.
Collapse
Affiliation(s)
- Chao Zhou
- 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
- Collaborative Innovation Center of Advanced Microstructures , Nanjing 210093 , China
| | - Jinyao Tang
- Department of Chemistry , University of Hong Kong , Hong Kong SAR 999077 , China
| | - Wei Wang
- School of Materials Science and Engineering , Harbin Institute of Technology (Shenzhen) , Shenzhen 518055 , China
| |
Collapse
|
64
|
Suzuki Y, Seki K. Possible influence of the Kuramoto length in a photo-catalytic water splitting reaction revealed by Poisson–Nernst–Planck equations involving ionization in a weak electrolyte. Chem Phys 2018. [DOI: 10.1016/j.chemphys.2018.01.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|
65
|
Malgaretti P, Popescu MN, Dietrich S. Self-diffusiophoresis induced by fluid interfaces. SOFT MATTER 2018; 14:1375-1388. [PMID: 29383367 DOI: 10.1039/c7sm02347b] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The influence of a fluid-fluid interface on self-phoresis of chemically active, axially symmetric, spherical colloids is analyzed. Distinct from the studies of self-phoresis for colloids trapped at fluid interfaces or in the vicinity of hard walls, here we focus on the issue of self-phoresis close to a fluid-fluid interface. In order to provide physically intuitive results highlighting the role played by the interface, the analysis is carried out for the case that the symmetry axis of the colloid is normal to the interface; moreover, thermal fluctuations are not taken into account. Similarly to what has been observed near hard walls, we find that such colloids can be set into motion even if their whole surface is homogeneously active. This is due to the anisotropy along the direction normal to the interface owing to the partitioning by diffusion, among the coexisting fluid phases, of the product of the chemical reaction taking place at the colloid surface. Different from results corresponding to hard walls, in the case of a fluid interface the direction of motion, i.e., towards the interface or away from it, can be controlled by tuning the physical properties of one of the two fluid phases. This effect is analyzed qualitatively and quantitatively, both by resorting to a far-field approximation and via an exact, analytical calculation which provides the means for a critical assessment of the approximate analysis.
Collapse
Affiliation(s)
- P Malgaretti
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569 Stuttgart, Germany.
| | | | | |
Collapse
|
66
|
Ning H, Zhang Y, Zhu H, Ingham A, Huang G, Mei Y, Solovev AA. Geometry Design, Principles and Assembly of Micromotors. MICROMACHINES 2018; 9:E75. [PMID: 30393351 PMCID: PMC6187850 DOI: 10.3390/mi9020075] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Revised: 02/06/2018] [Accepted: 02/07/2018] [Indexed: 01/19/2023]
Abstract
Discovery of bio-inspired, self-propelled and externally-powered nano-/micro-motors, rotors and engines (micromachines) is considered a potentially revolutionary paradigm in nanoscience. Nature knows how to combine different elements together in a fluidic state for intelligent design of nano-/micro-machines, which operate by pumping, stirring, and diffusion of their internal components. Taking inspirations from nature, scientists endeavor to develop the best materials, geometries, and conditions for self-propelled motion, and to better understand their mechanisms of motion and interactions. Today, microfluidic technology offers considerable advantages for the next generation of biomimetic particles, droplets and capsules. This review summarizes recent achievements in the field of nano-/micromotors, and methods of their external control and collective behaviors, which may stimulate new ideas for a broad range of applications.
Collapse
Affiliation(s)
- Huanpo Ning
- Department of Materials Science, Fudan University, 220 Handan Road, 200433 Shanghai, China.
| | - Yan Zhang
- Department of Materials Science, Fudan University, 220 Handan Road, 200433 Shanghai, China.
| | - Hong Zhu
- Department of Materials Science, Fudan University, 220 Handan Road, 200433 Shanghai, China.
| | - Andreas Ingham
- Department of Biology, University of Copenhagen, 5 Ole Maaløes Vej, DK-2200, 1165 København, Denmark.
| | - Gaoshan Huang
- Department of Materials Science, Fudan University, 220 Handan Road, 200433 Shanghai, China.
| | - Yongfeng Mei
- Department of Materials Science, Fudan University, 220 Handan Road, 200433 Shanghai, China.
| | - Alexander A Solovev
- Department of Materials Science, Fudan University, 220 Handan Road, 200433 Shanghai, China.
| |
Collapse
|
67
|
Katuri J, Uspal WE, Simmchen J, Miguel-López A, Sánchez S. Cross-stream migration of active particles. SCIENCE ADVANCES 2018; 4:eaao1755. [PMID: 29387790 PMCID: PMC5787385 DOI: 10.1126/sciadv.aao1755] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Accepted: 12/19/2017] [Indexed: 05/18/2023]
Abstract
For natural microswimmers, the interplay of swimming activity and external flow can promote robust directed motion, for example, propulsion against (upstream rheotaxis) or perpendicular to the direction of flow. These effects are generally attributed to their complex body shapes and flagellar beat patterns. Using catalytic Janus particles as a model experimental system, we report on a strong directional response that occurs for spherical active particles in a channel flow. The particles align their propulsion axes to be nearly perpendicular to both the direction of flow and the normal vector of a nearby bounding surface. We develop a deterministic theoretical model of spherical microswimmers near a planar wall that captures the experimental observations. We show how the directional response emerges from the interplay of shear flow and near-surface swimming activity. Finally, adding the effect of thermal noise, we obtain probability distributions for the swimmer orientation that semiquantitatively agree with the experimental distributions.
Collapse
Affiliation(s)
- Jaideep Katuri
- Institut de Bioenginyeria de Catalunya, The Barcelona Institute of Science and Technology, Baldiri I Reixac 10-12, 08028 Barcelona, Spain
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr 3, D-70569 Stuttgart, Germany
| | - William E. Uspal
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr 3, D-70569 Stuttgart, Germany
- IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany
- Corresponding author. (W.E.U.); (S.S.)
| | - Juliane Simmchen
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr 3, D-70569 Stuttgart, Germany
| | - Albert Miguel-López
- Institut de Bioenginyeria de Catalunya, The Barcelona Institute of Science and Technology, Baldiri I Reixac 10-12, 08028 Barcelona, Spain
| | - Samuel Sánchez
- Institut de Bioenginyeria de Catalunya, The Barcelona Institute of Science and Technology, Baldiri I Reixac 10-12, 08028 Barcelona, Spain
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr 3, D-70569 Stuttgart, Germany
- Institució Catalana de Recerca i Estudis Avancats, Passeig Lluís Companys, 23, 08010, Barcelona, Spain
- Corresponding author. (W.E.U.); (S.S.)
| |
Collapse
|
68
|
Zhang K, Fraxedas J, Sepulveda B, Esplandiu MJ. Photochemically Activated Motors: From Electrokinetic to Diffusion Motion Control. ACS APPLIED MATERIALS & INTERFACES 2017; 9:44948-44953. [PMID: 29199814 DOI: 10.1021/acsami.7b15855] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Self-propelled micro/nanomotors that can transform chemical energy from the surrounding environment into mechanical motion are cutting edge nanotechnologies with potential applications in biomedicine and environmental remediation. These applications require full understanding of the propulsion mechanisms to improve the performance and controllability of the motors. In this work, we demonstrate that there are two competing chemomechanical mechanisms at semiconductor/metal (Si/Pt) micromotors in a pump configuration under visible light exposure. The first propulsion mechanism is driven by an electro-osmotic process stemmed from a photoactivation reaction mediated by H2O2, which takes place in two separated redox reactions at the Si and Pt interfaces. One reaction involves the oxidation of H2O2 at the silicon side, and the other the H2O2 reduction at the metal side. The second mechanism is not light responsive and is triggered by the redox decomposition of H2O2 exclusively at the Pt surface. We show that it is possible to enhance/suppress one mechanism over the other by tuning the surface roughness of the micromotor metal. More specifically, the actuation mechanism can be switched from light-controlled electrokinetics to light-insensitive diffusio-osmosis by only increasing the metal surface roughness. The different actuation mechanisms yield strikingly different fluid flow velocities, electric fields, and light sensitivities. Consequently, these findings are very relevant and can have a remarkable impact on the design and optimization of photoactivated catalytic devices and, in general, on bimetallic or insulating-metallic motors.
Collapse
Affiliation(s)
- Kuan Zhang
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST , Campus UAB, Bellaterra, 08193 Barcelona, Spain
- Universitat Autònoma de Barcelona (UAB) , Bellaterra E-08193, Spain
| | - Jordi Fraxedas
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST , Campus UAB, Bellaterra, 08193 Barcelona, Spain
| | - Borja Sepulveda
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST , Campus UAB, Bellaterra, 08193 Barcelona, Spain
| | - Maria J Esplandiu
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST , Campus UAB, Bellaterra, 08193 Barcelona, Spain
- Universitat Autònoma de Barcelona (UAB) , Bellaterra E-08193, Spain
| |
Collapse
|
69
|
Tuning the motility and directionality of self-propelled colloids. Sci Rep 2017; 7:14891. [PMID: 29097762 PMCID: PMC5668334 DOI: 10.1038/s41598-017-14126-0] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 10/04/2017] [Indexed: 11/11/2022] Open
Abstract
Microorganisms are able to overcome the thermal randomness of their surroundings by harvesting energy to navigate in viscous fluid environments. In a similar manner, synthetic colloidal microswimmers are capable of mimicking complex biolocomotion by means of simple self-propulsion mechanisms. Although experimentally the speed of active particles can be controlled by e.g. self-generated chemical and thermal gradients, an in-situ change of swimming direction remains a challenge. In this work, we study self-propulsion of half-coated spherical colloids in critical binary mixtures and show that the coupling of local body forces, induced by laser illumination, and the wetting properties of the colloid, can be used to finely tune both the colloid’s swimming speed and its directionality. We experimentally and numerically demonstrate that the direction of motion can be reversibly switched by means of the size and shape of the droplet(s) nucleated around the colloid, depending on the particle radius and the fluid’s ambient temperature. Moreover, the aforementioned features enable the possibility to realize both negative and positive phototaxis in light intensity gradients. Our results can be extended to other types of half-coated microswimmers, provided that both of their hemispheres are selectively made active but with distinct physical properties.
Collapse
|
70
|
Liebchen B, Marenduzzo D, Cates ME. Phoretic Interactions Generically Induce Dynamic Clusters and Wave Patterns in Active Colloids. PHYSICAL REVIEW LETTERS 2017; 118:268001. [PMID: 28707925 DOI: 10.1103/physrevlett.118.268001] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Indexed: 06/07/2023]
Abstract
We introduce a representative minimal model for phoretically interacting active colloids. Combining kinetic theory, linear stability analyses, and a general relation between self-propulsion and phoretic interactions in autodiffusiophoretic and autothermophoretic Janus colloids collapses the parameter space from six to two dimensionless parameters: area fraction and Péclet number. This collapse arises when the lifetime of the self-generated phoretic fields is not too short, and leads to a universal phase diagram showing that phoretic interactions generically induce pattern formation in typical Janus colloids, even at very low density. The resulting patterns include waves and dynamic aggregates closely resembling the living clusters found in experiments on dilute suspension of Janus colloids.
Collapse
Affiliation(s)
- Benno Liebchen
- SUPA, School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
| | - Davide Marenduzzo
- SUPA, School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
| | - Michael E Cates
- DAMTP, Centre for Mathematical Sciences, University of Cambridge, Cambridge CB3 0WA, United Kingdom
| |
Collapse
|
71
|
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: 37] [Impact Index Per Article: 5.3] [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
|