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Active Colloids on Fluid Interfaces. Curr Opin Colloid Interface Sci 2022. [DOI: 10.1016/j.cocis.2022.101629] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Guzmán E, Martínez-Pedrero F, Calero C, Maestro A, Ortega F, Rubio RG. A broad perspective to particle-laden fluid interfaces systems: from chemically homogeneous particles to active colloids. Adv Colloid Interface Sci 2022; 302:102620. [PMID: 35259565 DOI: 10.1016/j.cis.2022.102620] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2021] [Revised: 02/22/2022] [Accepted: 02/23/2022] [Indexed: 01/12/2023]
Abstract
Particles adsorbed to fluid interfaces are ubiquitous in industry, nature or life. The wide range of properties arising from the assembly of particles at fluid interface has stimulated an intense research activity on shed light to the most fundamental physico-chemical aspects of these systems. These include the mechanisms driving the equilibration of the interfacial layers, trapping energy, specific inter-particle interactions and the response of the particle-laden interface to mechanical perturbations and flows. The understanding of the physico-chemistry of particle-laden interfaces becomes essential for taking advantage of the particle capacity to stabilize interfaces for the preparation of different dispersed systems (emulsions, foams or colloidosomes) and the fabrication of new reconfigurable interface-dominated devices. This review presents a detailed overview of the physico-chemical aspects that determine the behavior of particles trapped at fluid interfaces. This has been combined with some examples of real and potential applications of these systems in technological and industrial fields. It is expected that this information can provide a general perspective of the topic that can be exploited for researchers and technologist non-specialized in the study of particle-laden interfaces, or for experienced researcher seeking new questions to solve.
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Affiliation(s)
- Eduardo Guzmán
- Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain; Unidad de Materia Condensada, Instituto Pluridisciplinar, Universidad Complutense de Madrid, Paseo Juan XXIII 1, 28040 Madrid, Spain.
| | - Fernando Martínez-Pedrero
- Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain.
| | - Carles Calero
- Departament de Física de la Matèria Condensada, Facultat de Física, Universitat de Barcelona, Avenida Diagonal 647, 08028 Barcelona, Spain; Institut de Nanociència i Nanotecnologia, IN2UB, Universitat de Barcelona, Avenida, Diagonal 647, 08028 Barcelona, Spain
| | - Armando Maestro
- Centro de Fı́sica de Materiales (CSIC, UPV/EHU)-Materials Physics Center MPC, Paseo Manuel de Lardizabal 5, 20018 San Sebastián, Spain; IKERBASQUE-Basque Foundation for Science, Plaza Euskadi 5, 48009 Bilbao, Spain
| | - Francisco Ortega
- Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain; Unidad de Materia Condensada, Instituto Pluridisciplinar, Universidad Complutense de Madrid, Paseo Juan XXIII 1, 28040 Madrid, Spain
| | - Ramón G Rubio
- Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain; Unidad de Materia Condensada, Instituto Pluridisciplinar, Universidad Complutense de Madrid, Paseo Juan XXIII 1, 28040 Madrid, Spain.
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Wittmann M, Popescu MN, Domínguez A, Simmchen J. Active spheres induce Marangoni flows that drive collective dynamics. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2021; 44:15. [PMID: 33683489 PMCID: PMC7940161 DOI: 10.1140/epje/s10189-020-00006-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Accepted: 12/21/2020] [Indexed: 05/26/2023]
Abstract
For monolayers of chemically active particles at a fluid interface, collective dynamics is predicted to arise owing to activity-induced Marangoni flow even if the particles are not self-propelled. Here, we test this prediction by employing a monolayer of spherically symmetric active [Formula: see text] particles located at an oil-water interface with or without addition of a nonionic surfactant. Due to the spherical symmetry, an individual particle does not self-propel. However, the gradients produced by the photochemical fuel degradation give rise to long-ranged Marangoni flows. For the case in which surfactant is added to the system, we indeed observe the emergence of collective motion, with dynamics dependent on the particle coverage of the monolayer. The experimental observations are discussed within the framework of a simple theoretical mean-field model.
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Affiliation(s)
- Martin Wittmann
- Technical University Dresden, Zellescher Weg 19, 01069 Dresden, Germany
| | - Mihail N. Popescu
- Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569 Stuttgart, Germany
| | - Alvaro Domínguez
- Física Teórica, Universidad de Sevilla, Apdo. 1065, 41080 Sevilla, Spain
- Instituto Carlos I de Física Teórica y Computacional, 18071 Granada, Spain
| | - Juliane Simmchen
- Technical University Dresden, Zellescher Weg 19, 01069 Dresden, Germany
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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.
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Affiliation(s)
- Alvaro Domínguez
- Física Teórica, Universidad de Sevilla, Apdo. 1065, E-41080 Sevilla, Spain.
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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.
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Affiliation(s)
- P Malgaretti
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569 Stuttgart, Germany.
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Malgaretti P, Popescu MN, Dietrich S. Active colloids at fluid interfaces. SOFT MATTER 2016; 12:4007-4023. [PMID: 27025167 DOI: 10.1039/c6sm00367b] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
If an active Janus particle is trapped at the interface between a liquid and a fluid, its self-propelled motion along the interface is affected by a net torque on the particle due to the viscosity contrast between the two adjacent fluid phases. For a simple model of an active, spherical Janus colloid we analyze the conditions under which translation occurs along the interface and we provide estimates of the corresponding persistence length. We show that under certain conditions the persistence length of such a particle is significantly larger than the corresponding one in the bulk liquid, which is in line with the trends observed in recent experimental studies.
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Affiliation(s)
- P Malgaretti
- Max-Planck-Institut fur Intelligente Systeme, Theory of Inhomogeneous Condensed Matter, Heisenbergstrasse 3, Stuttgart, Germany.
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Pototsky A, Thiele U, Stark H. Mode instabilities and dynamic patterns in a colony of self-propelled surfactant particles covering a thin liquid layer. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2016; 39:51. [PMID: 27145959 DOI: 10.1140/epje/i2016-16051-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Accepted: 03/25/2016] [Indexed: 06/05/2023]
Abstract
We consider a colony of point-like self-propelled surfactant particles (swimmers) without direct interactions that cover a thin liquid layer on a solid support. The particles predominantly swim normal to the free film surface with only a small component parallel to the film surface. The coupled dynamics of the swimmer density and film height profile is captured in a long-wave model allowing for diffusive and convective transport of the swimmers (including rotational diffusion). The dynamics of the film height profile is determined by i) the upward pushing force of the swimmers onto the liquid-gas interface, ii) the solutal Marangoni force due to gradients in the swimmer concentration, and iii) the rotational diffusion of the swimmers together with the in-plane active motion. After reviewing and extending the analysis of the linear stability of the uniform state, we analyse the fully nonlinear dynamic equations and show that point-like swimmers, which only interact via long-wave deformations of the liquid film, self-organise in highly regular (standing, travelling, and modulated waves) and various irregular patterns.
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Affiliation(s)
- Andrey Pototsky
- Department of Mathematics, Faculty of Science Engineering and Technology, Swinburne University of Technology, 3122, Hawthorn, Victoria, Australia
| | - Uwe Thiele
- Institut für Theoretische Physik, Westfälische Wilhelms-Universität Münster, Wilhelm Klemm Str. 9, 48149, Münster, Germany.
- Center of Nonlinear Science (CeNoS), Westfälische Wilhelms Universität Münster, Corrensstr. 2, 48149, Münster, Germany.
| | - Holger Stark
- Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstrasse 36, 10623, Berlin, Germany
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Xu X, Thiele U, Qian T. A Variational approach to thin film hydrodynamics of binary mixtures. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:085005. [PMID: 25651053 DOI: 10.1088/0953-8984/27/8/085005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
In order to model the dynamics of thin films of mixtures, solutions, and suspensions, a thermodynamically consistent formulation is needed such that various coexisting dissipative processes with cross couplings can be correctly described in the presence of capillarity, wettability, and mixing effects. In the present work, we apply Onsager's variational principle to the formulation of thin film hydrodynamics for binary fluid mixtures. We first derive the dynamic equations in two spatial dimensions, one along the substrate and the other normal to the substrate. Then, using long-wave asymptotics, we derive the thin film equations in one spatial dimension along the substrate. This enables us to establish the connection between the present variational approach and the gradient dynamics formulation for thin films. It is shown that for the mobility matrix in the gradient dynamics description, Onsager's reciprocal symmetry is automatically preserved by the variational derivation. Furthermore, using local hydrodynamic variables, our variational approach is capable of introducing diffusive dissipation beyond the limit of dilute solute. Supplemented with a Flory-Huggins-type mixing free energy, our variational approach leads to a thin film model that treats solvent and solute in a symmetric manner. Our approach can be further generalized to include more complicated free energy and additional dissipative processes.
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Affiliation(s)
- Xinpeng Xu
- Department of Mathematics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
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