1
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Farkas E, Dóra Kovács K, Szekacs I, Peter B, Lagzi I, Kitahata H, Suematsu NJ, Horvath R. Kinetic monitoring of molecular interactions during surfactant-driven self-propelled droplet motion by high spatial resolution waveguide sensing. J Colloid Interface Sci 2024; 677:352-364. [PMID: 39151228 DOI: 10.1016/j.jcis.2024.07.236] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2024] [Revised: 07/29/2024] [Accepted: 07/30/2024] [Indexed: 08/19/2024]
Abstract
HYPOTHESIS Self-driven actions, like motion, are fundamental characteristics of life. Today, intense research focuses on the kinetics of droplet motion. Quantifying macroscopic motion and exploring the underlying mechanisms are crucial in self-structuring and self-healing materials, advancements in soft robotics, innovations in self-cleaning environmental processes, and progress within the pharmaceutical industry. Usually, the driving forces inducing macroscopic motion act at the molecular scale, making their real-time and high-resolution investigation challenging. Label-free surface sensitive measurements with high lateral resolution could in situ measure both molecular-scale interactions and microscopic motion. EXPERIMENTS We employ surface-sensitive label-free sensors to investigate the kinetic changes in a self-assembled monolayer of the trimethyl(octadecyl)azanium chloride surfactant on a substrate surface during the self-propelled motion of nitrobenzene droplets. The adsorption-desorption of the surfactant at various concentrations, its removal due to the moving organic droplet, and rebuilding mechanisms at droplet-visited areas are all investigated with excellent time, spatial, and surface mass density resolution. FINDINGS We discovered concentration dependent velocity fluctuations, estimated the adsorbed amount of surfactant molecules, and revealed multilayer coverage at high concentrations. The desorption rate of surfactant (18.4 s-1) during the microscopic motion of oil droplets was determined by in situ differentiating between droplet visited and non-visited areas.
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Affiliation(s)
- Eniko Farkas
- Nanobiosensorics Laboratory, Institute of Technical Physics and Materials Science, HUN-REN Centre for Energy Research, 1121 Budapest, Hungary
| | - Kinga Dóra Kovács
- Nanobiosensorics Laboratory, Institute of Technical Physics and Materials Science, HUN-REN Centre for Energy Research, 1121 Budapest, Hungary; Department of Biological Physics, Eötvös Loránd University, 1117 Budapest, Hungary
| | - Inna Szekacs
- Nanobiosensorics Laboratory, Institute of Technical Physics and Materials Science, HUN-REN Centre for Energy Research, 1121 Budapest, Hungary
| | - Beatrix Peter
- Nanobiosensorics Laboratory, Institute of Technical Physics and Materials Science, HUN-REN Centre for Energy Research, 1121 Budapest, Hungary
| | - István Lagzi
- Department of Physics, Institute of Physics, Budapest University of Technology and Economics, Muegyetem rkp. 3, 1111 Budapest, Hungary; HUN-REN-BME Condensed Matter Physics Research Group, Budapest University of Technology and Economics, Muegyetem rkp. 3, 1111 Budapest, Hungary
| | - Hiroyuki Kitahata
- Graduate School of Science, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522, Japan
| | - Nobuhiko J Suematsu
- Meiji Institute of Advanced Study of Mathematical Sciences (MIMS), Meiji University, 4-21-1 Nakano, Tokyo 164-8525, Japan; Graduate School of Advanced Mathematical Sciences, Meiji University, 4-21-1 Nakano, Tokyo 164-8525, Japan.
| | - Robert Horvath
- Nanobiosensorics Laboratory, Institute of Technical Physics and Materials Science, HUN-REN Centre for Energy Research, 1121 Budapest, Hungary; Nanobiosensorics Laboratory, Institute of Biophysics, HUN-REN Biological Research Centre, Szeged, Hungary.
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2
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Yang Q, Jiang M, Picano F, Zhu L. Shaping active matter from crystalline solids to active turbulence. Nat Commun 2024; 15:2874. [PMID: 38570495 PMCID: PMC11258367 DOI: 10.1038/s41467-024-46520-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Accepted: 02/27/2024] [Indexed: 04/05/2024] Open
Abstract
Active matter drives its constituent agents to move autonomously by harnessing free energy, leading to diverse emergent states with relevance to both biological processes and inanimate functionalities. Achieving maximum reconfigurability of active materials with minimal control remains a desirable yet challenging goal. Here, we employ large-scale, agent-resolved simulations to demonstrate that modulating the activity of a wet phoretic medium alone can govern its solid-liquid-gas phase transitions and, subsequently, laminar-turbulent transitions in fluid phases, thereby shaping its emergent pattern. These two progressively emerging transitions, hitherto unreported, bring us closer to perceiving the parallels between active matter and traditional matter. Our work reproduces and reconciles seemingly conflicting experimental observations on chemically active systems, presenting a unified landscape of phoretic collective dynamics. These findings enhance the understanding of long-range, many-body interactions among phoretic agents, offer new insights into their non-equilibrium collective behaviors, and provide potential guidelines for designing reconfigurable materials.
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Affiliation(s)
- Qianhong Yang
- Department of Mechanical Engineering, National University of Singapore, Singapore, Singapore
| | - Maoqiang Jiang
- School of Naval Architecture, Ocean and Energy Power Engineering, Wuhan University of Technology, Wuhan, Hubei, PR China
| | - Francesco Picano
- Department of Industrial Engineering and CISAS "G. Colombo", University of Padova, Padova, Italy
| | - Lailai Zhu
- Department of Mechanical Engineering, National University of Singapore, Singapore, Singapore.
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3
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Nguindjel AD, Franssen SCM, Korevaar PA. Reconfigurable Droplet-Droplet Communication Mediated by Photochemical Marangoni Flows. J Am Chem Soc 2024; 146:6006-6015. [PMID: 38391388 PMCID: PMC10921405 DOI: 10.1021/jacs.3c12882] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2023] [Revised: 01/19/2024] [Accepted: 02/08/2024] [Indexed: 02/24/2024]
Abstract
Droplets are attractive building blocks for dynamic matter that organizes into adaptive structures. Communication among collectively operating droplets opens untapped potential in settings that vary from sensing, optics, protocells, computing, or adaptive matter. Inspired by the transmission of signals among decentralized units in slime mold Physarum polycephalum, we introduce a combination of surfactants, self-assembly, and photochemistry to establish chemical signal transfer among droplets. To connect droplets that float at an air-water interface, surfactant triethylene glycol monododecylether (C12E3) is used for its ability to self-assemble into wires called myelins. We show how the trajectory of these myelins can be directed toward selected photoactive droplets upon UV exposure. To this end, we developed a strategy for photocontrolled Marangoni flow, which comprises (1) the liquid crystalline coating formed at the surface of an oleic acid/sodium oleate (OA/NaO) droplet when in contact with water, (2) a photoacid generator that protonates sodium oleate upon UV exposure and therefore disintegrates the coating, and (3) the surface tension gradient that is generated upon depletion of the surfactant from the air-water interface by the uncoated droplet. Therefore, localized UV exposure of selected OA/NaO droplets results in attraction of the myelins such that they establish reconfigurable connections that self-organize among the C12E3 and OA/NaO droplets. As an example of communication, we demonstrate how the myelins transfer fluorescent dyes, which are selectively delivered in the droplet interior upon photochemical regulation of the liquid crystalline coating.
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Affiliation(s)
- Anne-Déborah
C. Nguindjel
- Institute for Molecules and
Materials, Radboud University, Heyendaalseweg 135, Nijmegen 6525 AJ, The Netherlands
| | - Stan C. M. Franssen
- Institute for Molecules and
Materials, Radboud University, Heyendaalseweg 135, Nijmegen 6525 AJ, The Netherlands
| | - Peter A. Korevaar
- Institute for Molecules and
Materials, Radboud University, Heyendaalseweg 135, Nijmegen 6525 AJ, The Netherlands
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4
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Ray S, Roy A. Simple model for self-propulsion of microdroplets in surfactant solution. Phys Rev E 2023; 108:035102. [PMID: 37849129 DOI: 10.1103/physreve.108.035102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Accepted: 08/23/2023] [Indexed: 10/19/2023]
Abstract
We propose a simple active hydrodynamic model for the self-propulsion of a liquid droplet suspended in micellar solutions. The self-propulsion of the droplet occurs by spontaneous breaking of isotropic symmetry and is studied using both analytical and numerical methods. The emergence of self-propulsion arises from the slow dissolution of the inner fluid into the outer micellar solution as filled micelles. We propose that the surface generation of filled micelles is the dominant reason for the self-propulsion of the droplet. The flow instability is due to the Marangoni stress generated by the nonuniform distribution of the surfactant molecules on the droplet interface. In our model, the driving parameter of the instability is the excess surfactant concentration above the critical micellar concentration, which directly correlates with the experimental observations. We consider various low-order modes of flow instability and show that the first mode becomes unstable through a supercritical bifurcation and is the only mode contributing to the swimming of the droplet. The flow fields around the droplet for these modes and their combined effects are also discussed.
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Affiliation(s)
- Swarnak Ray
- Soft Condensed Matter Group, Raman Research Institute, Bangalore 560080, India
| | - Arun Roy
- Soft Condensed Matter Group, Raman Research Institute, Bangalore 560080, India
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5
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Kaburagi M, Kojima T, Asakura K, Banno T. pH-Sensitive Controlled Motion of Micrometer-sized Oil Droplets in a Solution of Surfactants Containing Fumaric Acid Derivatives. J Oleo Sci 2022; 71:1319-1326. [PMID: 35965092 DOI: 10.5650/jos.ess22129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Self-propelled droplets are of considerable interest as an appropriate model for understanding the self-propulsion of objects in the fields of nonequilibrium physics and nonlinear science. Several research groups have reported the monodirectional motion of droplets, that is, chemotaxis, using stimuli-responsive materials. However, the precise control of chemotaxis remains challenging from the perspective of synthetic chemistry because chemotactic motion is primarily induced by the consumption of reactive oil or surfactants. Herein, we report a chemical system containing pH-responsive fumaric acid derivatives, in which the oil droplet exhibited positive chemotaxis over a wide pH range-from basic to acidic conditions. From the measurements of the interfacial tension between the oil and aqueous phases, it was deduced that the positive chemotaxis was due to heterogeneity in the interfacial tension of the droplet surface, which was accompanied by the production of surface-active compounds in the pH gradient in a linear-type channel.
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Affiliation(s)
- Mari Kaburagi
- Department of Applied Chemistry, Faculty of Science and Technology, Keio University
| | - Tomoya Kojima
- Department of Applied Chemistry, Faculty of Science and Technology, Keio University
| | - Kouichi Asakura
- Department of Applied Chemistry, Faculty of Science and Technology, Keio University
| | - Taisuke Banno
- Department of Applied Chemistry, Faculty of Science and Technology, Keio University
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6
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We the Droplets: A Constitutional Approach to Active and Self-Propelled Emulsions. Curr Opin Colloid Interface Sci 2022. [DOI: 10.1016/j.cocis.2022.101623] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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7
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Yucknovsky A, Rich BB, Gutkin S, Ramanthrikkovil Variyam A, Shabat D, Pokroy B, Amdursky N. Application of Super Photoacids in Controlling Dynamic Processes: Light-Triggering the Self-Propulsion of Oil Droplets. J Phys Chem B 2022; 126:6331-6337. [PMID: 35959566 DOI: 10.1021/acs.jpcb.2c04020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The dynamic control of pH-responsive systems is at the heart of many natural and artificial processes. Here, we use photoacids, molecules that dissociate only in their excited state and transfer their proton to nearby proton acceptors, for the dynamic control of processes. A problem arises when there is a need to protonate highly acidic acceptors. We solve this problem using super photoacids that have an excited-state pKa of -8, thus enabling them to protonate very weak proton acceptors. The process that we target is the light-triggered self-propulsion of droplets, initiated by an excited-state proton transfer (ESPT) from a super photoacid donor to a surfactant acceptor situated on the surface of the droplet with a pKa of ∼0. We first confirm using steady-state and time-resolved spectroscopy that a super photoacid can undergo ESPT to the acidic surfactant, whereas a "regular" photoacid cannot. Next, we show self-propulsion of the droplet upon irradiating the solvated super photoacid. We further confirm the protonation of the surfactant on the surface of the droplet using transient surface tension measurements. Our system is the first example of the application of super photoacids to control dynamic processes and opens new possibilities in the field of light-triggered dynamic systems.
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Affiliation(s)
- Anna Yucknovsky
- Schulich Faculty of Chemistry, Technion─Israel Institute of Technology, Haifa 3200003, Israel
| | - Benjamin B Rich
- Department of Materials Science & Engineering, Technion─Israel Institute of Technology, Haifa 3200003, Israel
| | - Sara Gutkin
- School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University, Tel Aviv 69978, Israel
| | | | - Doron Shabat
- School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Boaz Pokroy
- Department of Materials Science & Engineering, Technion─Israel Institute of Technology, Haifa 3200003, Israel
| | - Nadav Amdursky
- Schulich Faculty of Chemistry, Technion─Israel Institute of Technology, Haifa 3200003, Israel
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8
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Wentworth CM, Castonguay AC, Moerman PG, Meredith CH, Balaj RV, Cheon SI, Zarzar LD. Chemically Tuning Attractive and Repulsive Interactions between Solubilizing Oil Droplets. Angew Chem Int Ed Engl 2022; 61:e202204510. [PMID: 35678216 DOI: 10.1002/anie.202204510] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2022] [Indexed: 11/09/2022]
Abstract
Micellar solubilization is a transport process occurring in surfactant-stabilized emulsions that can lead to Marangoni flow and droplet motility. Active droplets exhibit self-propulsion and pairwise repulsion due to solubilization processes and/or solubilization products raising the droplet's interfacial tension. Here, we report emulsions with the opposite behavior, wherein solubilization decreases the interfacial tension and causes droplets to attract. We characterize the influence of oil chemical structure, nonionic surfactant structure, and surfactant concentration on the interfacial tensions and Marangoni flows of solubilizing oil-in-water drops. Three regimes corresponding to droplet "attraction", "repulsion" or "inactivity" are identified. We believe these studies contribute to a fundamental understanding of solubilization processes in emulsions and provide guidance as to how chemical parameters can influence the dynamics and chemotactic interactions between active droplets.
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Affiliation(s)
- Ciera M Wentworth
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
| | - Alexander C Castonguay
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
| | - Pepijn G Moerman
- Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Caleb H Meredith
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA
| | - Rebecca V Balaj
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
| | - Seong Ik Cheon
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
| | - Lauren D Zarzar
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA.,Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA.,Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA
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9
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10
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Wentworth CM, Castonguay AC, Moerman PG, Meredith CH, Balaj RV, Cheon SI, Zarzar LD. Chemically Tuning Attractive and Repulsive Interactions between Solubilizing Oil Droplets. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202204510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Ciera M. Wentworth
- Department of Chemistry The Pennsylvania State University University Park PA 16802 USA
| | | | - Pepijn G. Moerman
- Department of Chemical and Biomolecular Engineering Johns Hopkins University Baltimore MD 21218 USA
| | - Caleb H. Meredith
- Department of Materials Science and Engineering The Pennsylvania State University University Park PA 16802 USA
| | - Rebecca V. Balaj
- Department of Chemistry The Pennsylvania State University University Park PA 16802 USA
| | - Seong Ik Cheon
- Department of Chemistry The Pennsylvania State University University Park PA 16802 USA
| | - Lauren D. Zarzar
- Department of Chemistry The Pennsylvania State University University Park PA 16802 USA
- Department of Materials Science and Engineering The Pennsylvania State University University Park PA 16802 USA
- Materials Research Institute The Pennsylvania State University University Park PA 16802 USA
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11
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Babu D, Katsonis N, Lancia F, Plamont R, Ryabchun A. Motile behaviour of droplets in lipid systems. Nat Rev Chem 2022; 6:377-388. [PMID: 37117430 DOI: 10.1038/s41570-022-00392-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/14/2022] [Indexed: 01/08/2023]
Abstract
Motility is the capacity for living organisms to move autonomously and with purpose, and is essential to life. The transition from abiotic chemistry into motile cellular compartments has yet to be understood, but motile behaviour likely followed chemical evolution because primeval cell survival depended on scouting for resources effectively. Minimalistic motile systems provide an experimental framework to delineate the emergence mechanisms of such an evolutionary asset. In this Review, we discuss frontier developments in controlling the movement of droplets in lipid systems, in particular, chemotactic behaviours driven by fluctuations in interfacial tension, because of its simple mechanism and prebiotic relevance. Although most efforts have focused on designing oil droplet motility in lipid-rich aqueous solutions, we highlight that water droplets can also move in lipid-enriched oils. First, we describe how droplets evolve chemotactic motility in lipid systems. Next, we review how these oil droplets can adapt their movement to illumination conditions. Finally, we discuss examples where chemical reactivity brings complexity to motility. This work contributes to systems chemistry, where chemical reactions combined with physicochemical phenomena can yield new functions, such that a limited set of molecules can promote complex movement at larger functional scales by following the rules of molecular chemistry.
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Affiliation(s)
- Dhanya Babu
- Stratingh Institute for Chemistry, University of Groningen, Groningen, Netherlands
| | - Nathalie Katsonis
- Stratingh Institute for Chemistry, University of Groningen, Groningen, Netherlands.
| | - Federico Lancia
- Stratingh Institute for Chemistry, University of Groningen, Groningen, Netherlands
| | - Remi Plamont
- Stratingh Institute for Chemistry, University of Groningen, Groningen, Netherlands
| | - Alexander Ryabchun
- Stratingh Institute for Chemistry, University of Groningen, Groningen, Netherlands
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12
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Noguchi M, Yamada M, Sawada H. Analysis of different self-propulsion types of oil droplets based on electrostatic interaction effects. RSC Adv 2022; 12:18354-18362. [PMID: 35799924 PMCID: PMC9214862 DOI: 10.1039/d2ra02076a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Accepted: 06/15/2022] [Indexed: 11/21/2022] Open
Abstract
We found that the correlated motion of two oil droplets was classified into three self-propelled motions (follow-up motion, parallel motion, and repulsive motion) depending on the pH of the aqueous solution.
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Affiliation(s)
- Mika Noguchi
- Department of Applied Physics, School of Advanced Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
| | - Masato Yamada
- Department of Applied Physics, School of Advanced Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
| | - Hideyuki Sawada
- Faculty of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
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13
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Acceleration of lipid reproduction by emergence of microscopic motion. Nat Commun 2021; 12:2959. [PMID: 34011926 PMCID: PMC8134444 DOI: 10.1038/s41467-021-23022-1] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Accepted: 04/03/2021] [Indexed: 11/09/2022] Open
Abstract
Self-reproducing molecules abound in nature where they support growth and motion of living systems. In artificial settings, chemical reactions can also show complex kinetics of reproduction, however integrating self-reproducing molecules into larger chemical systems remains a challenge towards achieving higher order functionality. Here, we show that self-reproducing lipids can initiate, sustain and accelerate the movement of octanol droplets in water. Reciprocally, the chemotactic movement of the octanol droplets increases the rate of lipid reproduction substantially. Reciprocal coupling between bond-forming chemistry and droplet motility is thus established as an effect of the interplay between molecular-scale events (the self-reproduction of lipid molecules) and microscopic events (the chemotactic movement of the droplets). This coupling between molecular chemistry and microscopic motility offers alternative means of performing work and catalysis in micro-heterogeneous environments.
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14
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Galy PE, Rudiuk S, Morel M, Baigl D. Self-Propelled Water Drops on Bare Glass Substrates in Air: Fast, Controllable, and Easy Transport Powered by Surfactants. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:6916-6923. [PMID: 32074453 DOI: 10.1021/acs.langmuir.9b03727] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Self-propelled drops are capable of motion without external intervention. As such, they constitute attractive entities for fundamental investigations in active soft matter, hydrodynamics, and surface sciences, as well as promising systems for autonomous microfluidic operations. In contrast with most of the examples relying on organic drops or specifically treated substrates, here we describe the first system of nonreactive water drops in air that can propel themselves on a commercially available ordinary glass substrate that was used as received. This is achieved by exploiting the dynamic adsorption behavior of common n-alkyltrimethylammonium bromide (CnTAB) surfactants added to the drop. We precisely analyze the drop motion for a broad series of surfactants carrying n = 6 to 18 carbon atoms in their tail and establish how the motion characteristics (speed, probability of motion) are tuned by both the hydrophobicity and the concentration of the surfactant. We show that motion occurs regardless of the n value but only in a specific concentration range with a maximum speed at around one tenth of the critical micelle concentration (CMC/10) for most of the tested surfactants. Surfactants of intermediate hydrophobicity are shown to be the best candidates to power drops that can move at a high speed (1-10 cm s-1), the optimal performance being reached with [C12TAB] = 800 μM. We propose a mechanism where the motion originates from the anisotropic wettability of the substrate created by the electrostatic adsorption of surfactants beneath the moving drop. Simply drawing lines with a marker pen allows us to create guiding paths for drop motion and to achieve operations such as complex trajectory control, programmed drop fusion, drop refilling, as well as drop moving vertically against gravity. This work revisits the role of surfactants in dynamic wetting and self-propelled motion as well as brings an original strategy to build the future of microfluidics with lower-cost, simpler, and more autonomous portable devices that could be made available to everyone and everywhere.
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Affiliation(s)
- Pauline E Galy
- PASTEUR, Department of Chemistry, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France
| | - Sergii Rudiuk
- PASTEUR, Department of Chemistry, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France
| | - Mathieu Morel
- PASTEUR, Department of Chemistry, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France
| | - Damien Baigl
- PASTEUR, Department of Chemistry, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France
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15
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Dewangan NK, Conrad JC. Rotating oil droplets driven by motile bacteria at interfaces. SOFT MATTER 2019; 15:9368-9375. [PMID: 31693048 DOI: 10.1039/c9sm01570a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We show that oil droplets suspended near a liquid-solid interface can be driven to rotate by motile bacteria adhered to the droplet surface. Droplets rotate clockwise when viewed from the liquid side, due to symmetry-breaking hydrodynamic interactions of bacteria with the interface. The angular speed of rotation for droplets decreases as their size is increased. Differences in the speed of rotation driven by Escherichia coli, Shewanella haliotis, and Halomonas titanicae bacteria reflects differences in the number of bacteria adhered at the droplet surface and their interfacial affinity. Adding surfactant reduces the number of adherent bacteria and hence lowers the speed of rotation. Together, these results demonstrate that bacterial activity can be used to manipulate suspended droplets.
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Affiliation(s)
- Narendra K Dewangan
- Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204, USA.
| | - Jacinta C Conrad
- Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204, USA.
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16
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Kasuo Y, Kitahata H, Koyano Y, Takinoue M, Asakura K, Banno T. Start of Micrometer-Sized Oil Droplet Motion through Generation of Surfactants. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:13351-13355. [PMID: 31550892 DOI: 10.1021/acs.langmuir.9b01722] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Self-propelled motion of micrometer-sized oil droplets in surfactant solution has drawn much attention as an example of nonlinear life-like dynamics under far-from-equilibrium conditions. The driving force of this motion is thought to be induced by Marangoni convection based on heterogeneity in the interfacial tension at the droplet surface. Here, to clarify the required conditions for the self-propelled motion of oil droplets, we have constructed a chemical system, where oil droplet motion is induced by the production of 1,2,3-triazole-containing surfactants through the Cu-catalyzed azide-alkyne cycloaddition reaction. From the results of the visualization and analysis of flow fields around the droplet, the motion of the droplets could be attributed to the formation of flow fields, which achieved sufficient strength caused by the in situ production of surfactants at the droplet surface.
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Affiliation(s)
- Yui Kasuo
- Department of Applied Chemistry, Faculty of Science and Technology , Keio University , 3-14-1 Hiyoshi , Kohoku-ku, Yokohama 223-8522 , Japan
| | - Hiroyuki Kitahata
- Department of Physics, Graduate School of Science , Chiba University , 1-33 Yayoi-cho , Inage-ku, Chiba 263-8522 , Japan
| | - Yuki Koyano
- Department of Physics , Tohoku University , 6-3 Aramaki-Aza-Aoba , Aoba-ku, Miyagi 980-8578 , Japan
| | - Masahiro Takinoue
- Department of Computer Science , Tokyo Institute of Technology , 4259 Nagatsuta-cho , Midori-ku , Yokohama 226-8502 , Japan
| | - Kouichi Asakura
- Department of Applied Chemistry, Faculty of Science and Technology , Keio University , 3-14-1 Hiyoshi , Kohoku-ku, Yokohama 223-8522 , Japan
| | - Taisuke Banno
- Department of Applied Chemistry, Faculty of Science and Technology , Keio University , 3-14-1 Hiyoshi , Kohoku-ku, Yokohama 223-8522 , Japan
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17
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Yoshioka J, Fukao K. Horizontal transportation of a Maltese cross pattern in nematic liquid crystalline droplets under a temperature gradient. Phys Rev E 2019; 99:022702. [PMID: 30934222 DOI: 10.1103/physreve.99.022702] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Indexed: 11/07/2022]
Abstract
Flow and director fields strongly couple with each other in liquid crystalline systems, and herein we discuss the coupling effect in cylindrical and spherical-cap droplets formed by nematic liquid crystal. Applying a temperature gradient to droplets dispersed in a liquid solvent, we observed a crosslike texture in the droplets moved toward the high-temperature side, indicating that the director field was deformed from equilibrium. Additionally, measurement of the flow field revealed that a convective flow was induced in the droplets under temperature gradient. These results suggested that the director deformation in the droplet was induced by convection. By designing a simplified model based on this, we theoretically analyzed the above phenomenon based on Onsager's variational principle. The results show that the phenomenon was well described by a balance of surface energy gradient with viscous and elastic forces.
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Affiliation(s)
- Jun Yoshioka
- Department of Physical Sciences, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-0058, Japan
| | - Koji Fukao
- Department of Physical Sciences, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-0058, Japan
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18
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Morohashi H, Imai M, Toyota T. Construction of a chemical motor-movable frame assembly based on camphor grains using water-floating 3D-printed models. Chem Phys Lett 2019. [DOI: 10.1016/j.cplett.2019.02.034] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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19
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Bian X, Huang H, Chen L. Motion of droplets into hydrophobic parallel plates. RSC Adv 2019; 9:32278-32287. [PMID: 35530760 PMCID: PMC9072857 DOI: 10.1039/c9ra05135j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2019] [Accepted: 09/16/2019] [Indexed: 11/21/2022] Open
Abstract
Due to the superior operability and good anti-interference, the prospect of controlling microdroplets using a parallel plate structure (PPS) is very promising. However, in practical applications, droplets in such structures are often affected by various factors, resulting in deformation, evaporation, stress rupture and other phenomena, leading to equipment failure. Therefore, how to simply and effectively transfer liquid droplets to PPS to maintain the stable and efficient operation of the system has become an urgent problem to be solved. In this paper, a simple and effective ratchet-like strategy (relaxing and squeezing actions) is introduced to transfer droplets. To analyze the mechanism of the strategy and optimize the control, we conduct this study from three aspects. First, the droplet movement trend is obtained by analyzing the pressure between SPS and PPS. Second, the reasons why the droplet can achieve this inward motion are investigated. Through theoretical analysis, which is also proven by simulations and experiments, we creatively put forward that the asymmetric change of the contact angle (CA) induced by the asymmetric structure is the fundamental cause of this kind of motion. Due to the asymmetric change of the contact angle, the CA in the PPS will reach the advancing angle first in the squeezing process, and the CA in the SPS will reach the receding angle first in the relaxing process, thus causing the inward movement of the droplet. Third, to optimize this strategy, the effects of the following governing parameters are researched individually based on the corresponding simulations and experiments: the control parameters (the initial gap width of the PPS H0 and the amount of squeezing and relaxing of ΔH) and the thickness of the top plate. Subsequently, an optimized ratchet-like cycle is achieved. In summary, these findings not only provide a new method by which to realize the movement of droplets toward hydrophobic PPSs but also creatively point out the cause of the ratchet strategy, which can be applied in many microfluidics fields. A simple and effective ratchet-like strategy is introduced to transfer droplets. We creatively put forward that the asymmetric change of the contact angle induced by the asymmetric structure is the fundamental cause of this kind of motion.![]()
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Affiliation(s)
- Xiongheng Bian
- Robotics & Microsystem Center
- Collaborative Innovation Center of Suzhou Nano Science and Technology
- Soochow University
- Suzhou 215123
- China
| | - Haibo Huang
- Robotics & Microsystem Center
- Collaborative Innovation Center of Suzhou Nano Science and Technology
- Soochow University
- Suzhou 215123
- China
| | - Liguo Chen
- Robotics & Microsystem Center
- Collaborative Innovation Center of Suzhou Nano Science and Technology
- Soochow University
- Suzhou 215123
- China
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20
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Sugiyama H, Toyota T. Toward Experimental Evolution with Giant Vesicles. Life (Basel) 2018; 8:life8040053. [PMID: 30384503 PMCID: PMC6316375 DOI: 10.3390/life8040053] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Revised: 10/30/2018] [Accepted: 10/30/2018] [Indexed: 01/19/2023] Open
Abstract
Experimental evolution in chemical models of cells could reveal the fundamental mechanisms of cells today. Various chemical cell models, water-in-oil emulsions, oil-on-water droplets, and vesicles have been constructed in order to conduct research on experimental evolution. In this review, firstly, recent studies with these candidate models are introduced and discussed with regards to the two hierarchical directions of experimental evolution (chemical evolution and evolution of a molecular self-assembly). Secondly, we suggest giant vesicles (GVs), which have diameters larger than 1 µm, as promising chemical cell models for studying experimental evolution. Thirdly, since technical difficulties still exist in conventional GV experiments, recent developments of microfluidic devices to deal with GVs are reviewed with regards to the realization of open-ended evolution in GVs. Finally, as a future perspective, we link the concept of messy chemistry to the promising, unexplored direction of experimental evolution in GVs.
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Affiliation(s)
- Hironori Sugiyama
- Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.
| | - Taro Toyota
- Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.
- Universal Biology Institute, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.
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21
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Hirono A, Toyota T, Asakura K, Banno T. Locomotion Mode of Micrometer-Sized Oil Droplets in Solutions of Cationic Surfactants Having Ester or Ether Linkages. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:7821-7826. [PMID: 29878786 DOI: 10.1021/acs.langmuir.8b01352] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Micrometer-sized self-propelled oil droplets under a far-from-equilibrium condition have drawn much attention because of their potential as a dynamic model for the chemical machinery in living organisms. To clarify the effect of interactions between the system components (surfactant, oil, and water) on the locomotion mode of droplets, we investigated the behaviors of oil droplets composed of n-heptyloxybenzaldehyde (HBA) in solutions of cationic surfactants having or not having an ester or an ether linkage. It was observed that in solutions of cationic surfactants having an ester or an ether linkage, spherical HBA droplets self-propelled by changing their direction frequently. On the other hand, when this functional group is absent, a slow self-propelled motion of the oil droplets concurrent with the evolution of aggregates on their surface was observed. From the results of measurement of interfacial tension and assessment of self-emulsification, we determined that the attractive interactions of cationic surfactants without an ester or an ether linkage with HBA are stronger than those having the linkage. The difference in the locomotion mode of oil droplets is probably explained from the viewpoint of the interactions among the system components.
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Affiliation(s)
- Ayana Hirono
- Department of Applied Chemistry, Faculty of Science and Technology , Keio University , 3-14-1 Hiyoshi , Kohoku-ku, Yokohama 223-8522 , Japan
| | - Taro Toyota
- Department of Basic Science, Graduate School of Arts and Sciences , The University of Tokyo , 3-8-1 Komaba , Meguro-ku, Tokyo 153-8902 , Japan
| | - Kouichi Asakura
- Department of Applied Chemistry, Faculty of Science and Technology , Keio University , 3-14-1 Hiyoshi , Kohoku-ku, Yokohama 223-8522 , Japan
| | - Taisuke Banno
- Department of Applied Chemistry, Faculty of Science and Technology , Keio University , 3-14-1 Hiyoshi , Kohoku-ku, Yokohama 223-8522 , Japan
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22
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Suga M, Suda S, Ichikawa M, Kimura Y. Self-propelled motion switching in nematic liquid crystal droplets in aqueous surfactant solutions. Phys Rev E 2018; 97:062703. [PMID: 30011466 DOI: 10.1103/physreve.97.062703] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2018] [Indexed: 06/08/2023]
Abstract
The self-propelled motions of micron-sized nematic liquid crystal droplets in an aqueous surfactant solution have been studied by tracking individual droplets over long time periods. Switching between self-propelled modes is observed as the droplet size decreases at a nearly constant dissolution rate: from random to helical and then straight motion. The velocity of the droplet decreases with its size for straight and helical motions but is independent of size for random motion. The switching between helical and straight motions is found to be governed by the self-propelled velocity, and is confirmed by experiments at various surfactant concentrations. The helical motion appears along with a shifting of a point defect from the self-propelled direction of the droplet. The critical velocity for this shift of the defect position is found to be related with the Ericksen number, which is defined by the ratio of the viscous and elastic stresses. In a thin cell whose thickness is smaller than that of the initial droplet size, the droplets show more complex trajectories, including "figure-8s" and zigzags. The appearance of those characteristic motions is attributed to autochemotaxis of the droplet.
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Affiliation(s)
- Mariko Suga
- Department of Physics, School of Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
| | - Saori Suda
- Department of Physics, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan
| | - Masatoshi Ichikawa
- Department of Physics, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan
| | - Yasuyuki Kimura
- Department of Physics, School of Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
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23
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Suematsu NJ, Nakata S. Evolution of Self-Propelled Objects: From the Viewpoint of Nonlinear Science. Chemistry 2018; 24:6308-6324. [DOI: 10.1002/chem.201705171] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Indexed: 01/04/2023]
Affiliation(s)
- Nobuhiko J. Suematsu
- Graduate School of Advanced Mathematical Sciences, Meiji Institute for Advanced Study of Mathematical Sciences (MIMS); Meiji University; Nakano 4-21-1 Tokyo 164-8525 Japan
| | - Satoshi Nakata
- Graduate School of Sciences; Hiroshima University; Kagamiyama 1-3-1 Higashi-Hiroshima 739-8526 Japan
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24
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Abstract
Liquid droplets are very simple objects present in our everyday life. They are extremely important for many natural phenomena as well as for a broad variety of industrial processes. The conventional research areas in which the droplets are studied include physical chemistry, fluid mechanics, chemical engineering, materials science, and micro- and nanotechnology. Typical studies include phenomena such as condensation and droplet formation, evaporation of droplets, or wetting of surfaces. The present article reviews the recent literature that employs droplets as animated soft matter. It is argued that droplets can be considered as liquid robots possessing some characteristics of living systems, and such properties can be applied to unconventional computing through maze solving or operation in logic gates. In particular, the lifelike properties and behavior of liquid robots, namely (i) movement, (ii) self-division, and (iii) group dynamics, will be discussed.
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25
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Nagasaka Y, Tanaka S, Nehira T, Amimoto T. Spontaneous emulsification and self-propulsion of oil droplets induced by the synthesis of amino acid-based surfactants. SOFT MATTER 2017; 13:6450-6457. [PMID: 28876349 DOI: 10.1039/c7sm01117b] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
It is well known that oil droplets in or on water exhibit spontaneous movement induced by surfactants, and this self-propulsion is regarded as an important factor in droplet-based models for a living cell. We report here an oil-droplet system spontaneously producing amino acid-based surfactants, which are then utilized for the droplets' self-propulsion. Thus this system is an active system capable of producing the fuel for the propulsion by itself, which can be used as a conceptual model for cell metabolism.
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Affiliation(s)
- Yuriko Nagasaka
- Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan.
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26
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Liu C, Sun J, Li J, Xiang C, Che L, Wang Z, Zhou X. Long-range spontaneous droplet self-propulsion on wettability gradient surfaces. Sci Rep 2017; 7:7552. [PMID: 28790426 PMCID: PMC5548791 DOI: 10.1038/s41598-017-07867-5] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Accepted: 07/04/2017] [Indexed: 11/09/2022] Open
Abstract
The directional and long-range droplet transportation is of great importance in microfluidic systems. However, it usually requires external energy input. Here we designed a wettability gradient surface that can drive droplet motion by structural topography. The surface has a wettability gradient range of over 150° from superhydrophobic to hydrophilic, which was achieved by etching silicon nanopillars and adjusting the area of hydrophilic silicon dioxide plane. We conducted force analysis to further reveal the mechanism for droplet self-propulsion, and found that the nanostructures are critical to providing a large driving force and small resistance force. Theoretical calculation has been used to analyze the maximal self-propulsion displacement on different gradient surfaces with different volumes of droplets. On this basis, we designed several surfaces with arbitrary paths, which achieved directional and long-range transportation of droplet. These results clarify a driving mechanism for droplet self-propulsion on wettability gradient surfaces, and open up new opportunities for long-range and directional droplet transportation in microfluidic system.
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Affiliation(s)
- Chaoran Liu
- Science and Technology on Microsystem Laboratory, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, 200050, China.,School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Jing Sun
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong, 999077, China
| | - Jing Li
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong, 999077, China
| | - Chenghao Xiang
- Science and Technology on Microsystem Laboratory, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, 200050, China.,School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Lufeng Che
- Science and Technology on Microsystem Laboratory, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, 200050, China. .,College of Biomedical Engineering and Instrument Science, Zhejiang University, Hangzhou, 310027, China.
| | - Zuankai Wang
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong, 999077, China.
| | - Xiaofeng Zhou
- Science and Technology on Microsystem Laboratory, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, 200050, China.
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27
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Singh V, Wu CJ, Sheng YJ, Tsao HK. Self-Propulsion and Shape Restoration of Aqueous Drops on Sulfobetaine Silane Surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:6182-6191. [PMID: 28551998 DOI: 10.1021/acs.langmuir.7b01120] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The motion of droplets on typical surfaces is generally halted by contact line pinning associated with contact angle hysteresis. In this study, it was shown that, on a zwitterionic sulfobetaine silane (SBSi)-coated surface, aqueous drops with appropriate solutes can demonstrate hysteresis-free behavior, whereas a pure water drop shows spontaneous spreading. By adding solutes such as polyethylene glycol, 2(2-butoxy ethoxy) ethanol, or sodium n-dodecyl sulfate, an aqueous drop with a small contact angle (disappearance of spontaneous spreading) was formed on SBSi surfaces. The initial drop shape was readily relaxed back to a circular shape (hysteresis-free behavior), even upon severe disturbances. Moreover, it was interesting to observe the self-propulsion of such a drop on horizontal SBSi surfaces in the absence of externally provided stimuli. The self-propelled drop tends to follow a random trajectory, and the continuous movement can last for at least 10 min. This self-propelled random motion can be attributed to the combined effects of the hysteresis-free surface and the Marangoni stress. The former comes from the total wetting property of the surface, while the latter originates from surface tension gradient due to fluctuating evaporation rates along the drop border.
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Affiliation(s)
- Vickramjeet Singh
- Department of Chemical and Materials Engineering, National Central University , Jhongli 320, Taiwan
| | - Cyuan-Jhang Wu
- Department of Chemical and Materials Engineering, National Central University , Jhongli 320, Taiwan
| | - Yu-Jane Sheng
- Department of Chemical Engineering, National Taiwan University , Taipei 106, Taiwan
| | - Heng-Kwong Tsao
- Department of Chemical and Materials Engineering, National Central University , Jhongli 320, Taiwan
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28
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Satoh Y, Sogabe Y, Kayahara K, Tanaka S, Nagayama M, Nakata S. Self-inverted reciprocation of an oil droplet on a surfactant solution. SOFT MATTER 2017; 13:3422-3430. [PMID: 28436513 DOI: 10.1039/c7sm00252a] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Self-motion of an oil droplet was investigated on a sodium dodecyl sulfate (SDS) aqueous phase. With an increase in the concentration of SDS, the nature of self-motion of a butyl salicylate (BS) droplet as the oil droplet was changed, i.e., no motion, reciprocation with a small amplitude, and reciprocation with a large amplitude, which was a value close to the half-length of the chamber. The interfacial tension, contact angle, and convective flow around the droplet were measured to clarify the driving force of reciprocation. The mechanisms of two types of reciprocation and mode-change were discussed in terms of the adsorption of SDS molecules at the BS/water interface and the dissolution of a mixture of BS and SDS into the bulk phase, the convective flow, and the Young's equation. The features of reciprocation and mode-change depending on the concentration of SDS were qualitatively reproduced by numerical calculation based on an equation of motion and the kinetics of SDS and BS at the air/aqueous interface.
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Affiliation(s)
- Yusuke Satoh
- Graduate School of Science, Hokkaido University, N10W8, Kita-Ward, Sapporo, 060-0810, Japan
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29
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Banno T, Tanaka Y, Asakura K, Toyota T. Self-Propelled Oil Droplets and Their Morphological Change to Giant Vesicles Induced by a Surfactant Solution at Low pH. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:9591-9597. [PMID: 27580350 DOI: 10.1021/acs.langmuir.6b02449] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Unique dynamics using inanimate molecular assemblies based on soft matter have drawn much attention for demonstrating far-from-equilibrium chemical systems. However, there are no soft matter systems that exhibit a possible pathway linking the self-propelled oil droplets to formation of giant vesicles stimulated by low pH. In this study, we conceived an experimental oil-in-water emulsion system in which flocculated particles composed of a imine-containing oil transformed to spherical oil droplets that self-propelled and, after coming to rest, formed membranous figures. Finally, these figures became giant vesicles. From NMR, pH curves, and surface tension measurements, we determined that this far-from-equilibrium phenomenon was due to the acidic hydrolysis of the oil, which produced a benzaldehyde derivative as an oil component and a primary amine as a surfactant precursor, and the dynamic behavior of the hydrolytic products in the emulsion system. These findings afforded us a potential linkage between mobile droplet-based protocells and vesicle-based protocells stimulated by low pH.
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Affiliation(s)
- Taisuke Banno
- Department of Applied Chemistry, Faculty of Science and Technology, Keio University , 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
| | - Yuki Tanaka
- Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo , 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
| | - Kouichi Asakura
- Department of Applied Chemistry, Faculty of Science and Technology, Keio University , 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
| | - Taro Toyota
- Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo , 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
- Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency , 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
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30
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Schmitt M, Stark H. Active Brownian motion of emulsion droplets: Coarsening dynamics at the interface and rotational diffusion. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2016; 39:80. [PMID: 27562831 DOI: 10.1140/epje/i2016-16080-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Revised: 06/13/2016] [Accepted: 07/19/2016] [Indexed: 06/06/2023]
Abstract
A micron-sized droplet of bromine water immersed in a surfactant-laden oil phase can swim (S. Thutupalli, R. Seemann, S. Herminghaus, New J. Phys. 13 073021 (2011). The bromine reacts with the surfactant at the droplet interface and generates a surfactant mixture. It can spontaneously phase-separate due to solutocapillary Marangoni flow, which propels the droplet. We model the system by a diffusion-advection-reaction equation for the mixture order parameter at the interface including thermal noise and couple it to fluid flow. Going beyond previous work, we illustrate the coarsening dynamics of the surfactant mixture towards phase separation in the axisymmetric swimming state. Coarsening proceeds in two steps: an initially slow growth of domain size followed by a nearly ballistic regime. On larger time scales thermal fluctuations in the local surfactant composition initiates random changes in the swimming direction and the droplet performs a persistent random walk, as observed in experiments. Numerical solutions show that the rotational correlation time scales with the square of the inverse noise strength. We confirm this scaling by a perturbation theory for the fluctuations in the mixture order parameter and thereby identify the active emulsion droplet as an active Brownian particle.
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Affiliation(s)
- M Schmitt
- Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstraße 36, 10623, Berlin, Germany.
| | - H Stark
- Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstraße 36, 10623, Berlin, Germany
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31
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Krüger C, Klös G, Bahr C, Maass CC. Curling Liquid Crystal Microswimmers: A Cascade of Spontaneous Symmetry Breaking. PHYSICAL REVIEW LETTERS 2016; 117:048003. [PMID: 27494501 DOI: 10.1103/physrevlett.117.048003] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2016] [Indexed: 06/06/2023]
Abstract
We report curling self-propulsion in aqueous emulsions of common mesogenic compounds. Nematic liquid crystal droplets self-propel in a surfactant solution with concentrations above the critical micelle concentration while undergoing micellar solubilization [Herminghaus et al., Soft Matter 10, 7008 (2014)]. We analyzed trajectories both in a Hele-Shaw geometry and in a 3D setup at variable buoyancy. The coupling between the nematic director field and the convective flow inside the droplet leads to a second symmetry breaking which gives rise to curling motion in 2D. This is demonstrated through a reversible transition to nonhelical persistent swimming by heating to the isotropic phase. Furthermore, autochemotaxis can spontaneously break the inversion symmetry, leading to helical trajectories in 3D.
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Affiliation(s)
- Carsten Krüger
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), Am Faßberg 17, 37077 Göttingen, Germany
| | - Gunnar Klös
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), Am Faßberg 17, 37077 Göttingen, Germany
| | - Christian Bahr
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), Am Faßberg 17, 37077 Göttingen, Germany
| | - Corinna C Maass
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), Am Faßberg 17, 37077 Göttingen, Germany
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32
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Krüger C, Bahr C, Herminghaus S, Maass CC. Dimensionality matters in the collective behaviour of active emulsions. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2016; 39:64. [PMID: 27342105 DOI: 10.1140/epje/i2016-16064-y] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Accepted: 06/02/2016] [Indexed: 06/06/2023]
Abstract
The behaviour of artificial microswimmers consisting of droplets of a mesogenic oil immersed in an aqueous surfactant solution depends qualitatively on the conditions of dimensional confinement; ranging from only transient aggregates in Hele-Shaw geometries to hexagonally packed, convection-driven clusters when sedimenting in an unconfined reservoir. We study the effects of varying the swimmer velocity, the height of the reservoir, and the buoyancy of the droplet swimmers. Two simple adjustments of the experimental setting lead to a suppression of clustering: either a decrease of the reservoir height below a certain value, or a match of the densities of droplets and surrounding phase, showing that the convection is the key mechanism for the clustering behaviour.
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Affiliation(s)
- Carsten Krüger
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), Am Faßberg 17, 37077, Göttingen, Germany.
| | - Christian Bahr
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), Am Faßberg 17, 37077, Göttingen, Germany
| | - Stephan Herminghaus
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), Am Faßberg 17, 37077, Göttingen, Germany
| | - Corinna C Maass
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), Am Faßberg 17, 37077, Göttingen, Germany
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33
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Suzuki K, Sugawara T. Phototaxis of Oil Droplets Comprising a Caged Fatty Acid Tightly Linked to Internal Convection. Chemphyschem 2016; 17:2300-3. [DOI: 10.1002/cphc.201600273] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Indexed: 11/11/2022]
Affiliation(s)
- Kentaro Suzuki
- Department of Chemistry; Faculty of Science; Kanagawa University; 2946 Tsuchiya, Hiratsuka Kanagawa 259-1293 Japan
| | - Tadashi Sugawara
- Department of Chemistry; Faculty of Science; Kanagawa University; 2946 Tsuchiya, Hiratsuka Kanagawa 259-1293 Japan
- Toyota Physical and Chemical Research Institute; 41-1, Yokomichi, Nagakute Aichi 480-1192 Japan
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34
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Nakata S, Nagayama M, Kitahata H, Suematsu NJ, Hasegawa T. Physicochemical design and analysis of self-propelled objects that are characteristically sensitive to environments. Phys Chem Chem Phys 2015; 17:10326-38. [PMID: 25826144 DOI: 10.1039/c5cp00541h] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The development of self-propelled motors that mimic biological motors is an important challenge for the transport of either themselves or some material in a small space, since biological systems exhibit high autonomy and various types of responses, such as taxis and swarming. In this perspective, we review non-living systems that behave like living matter. We especially focus on nonlinearity to enhance autonomy and the response of the system, since characteristic nonlinear phenomena, such as oscillation, synchronization, pattern formation, bifurcation, and hysteresis, are coupled to self-motion of which driving force is the difference in the interfacial tension. Mathematical modelling based on reaction-diffusion equations and equations of motion as well as physicochemical analysis from the point of view of the molecular structure are also important for the design of non-living motors that mimic living motors.
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Affiliation(s)
- Satoshi Nakata
- Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan.
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Tanaka S, Sogabe Y, Nakata S. Spontaneous change in trajectory patterns of a self-propelled oil droplet at the air-surfactant solution interface. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 91:032406. [PMID: 25871122 DOI: 10.1103/physreve.91.032406] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Indexed: 05/28/2023]
Abstract
Trajectory-pattern formation of a self-propelled oil droplet floating on the surface of a surfactant solution in a circular dish is studied both experimentally and by simulation. The Marangoni effect induced by the dissolution of oil in the solution drives the droplet's motion. The trajectories spontaneously organize into several patterns including circular, knot-forming, back-and-forth, and irregular ones. They are either global patterns, whose center corresponds to the dish center, or other local patterns. Our simple model consisting of three forces, the driving force, the viscous resistance, and the repulsion from the boundary, successfully reproduces the global trajectory patterns including the power spectrum of the droplet speed.
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Affiliation(s)
- Shinpei Tanaka
- Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan
| | - Yoshimi Sogabe
- Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan
| | - Satoshi Nakata
- Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan
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Banno T, Kuroha R, Miura S, Toyota T. Multiple-division of self-propelled oil droplets through acetal formation. SOFT MATTER 2015; 11:1459-1463. [PMID: 25601308 DOI: 10.1039/c4sm02631d] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We demonstrate a novel system that exhibits both self-propelled motion and division of micrometer-sized oil droplets induced by chemical conversion of the system components. Such unique dynamics were observed in an oil-in-water emulsion of a benzaldehyde derivative, an alkanol and a cationic surfactant at a low pH.
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Affiliation(s)
- Taisuke Banno
- Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan.
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Florea L, Wagner K, Wagner P, Wallace GG, Benito-Lopez F, Officer DL, Diamond D. Photo-chemopropulsion--light-stimulated movement of microdroplets. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2014; 26:7339-7345. [PMID: 25236879 DOI: 10.1002/adma.201403007] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Revised: 08/14/2014] [Indexed: 06/03/2023]
Abstract
The controlled movement of a chemical container by the light-activated expulsion of a chemical fuel, named here "photo-chemopropulsion", is an exciting new development in the array of mechanisms employed for controlling the movement of microvehicles, herein represented by lipid-based microdroplets. This "chemopropulsion" effect can be switched on and off, and is fully reversible.
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Affiliation(s)
- Larisa Florea
- Insight Centre for Data Analytics, National Centre for Sensor Research, Dublin City University, Dublin, 9, Ireland
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Herminghaus S, Maass CC, Krüger C, Thutupalli S, Goehring L, Bahr C. Interfacial mechanisms in active emulsions. SOFT MATTER 2014; 10:7008-22. [PMID: 24924906 DOI: 10.1039/c4sm00550c] [Citation(s) in RCA: 112] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Active emulsions, i.e., emulsions whose droplets perform self-propelled motion, are of tremendous interest for mimicking collective phenomena in biological populations such as phytoplankton and bacterial colonies, but also for experimentally studying rheology, pattern formation, and phase transitions in systems far from thermal equilibrium. For fuelling such systems, molecular processes involving the surfactants which stabilize the emulsions are a straightforward concept. We outline and compare two different types of reactions, one which chemically modifies the surfactant molecules, the other which transfers them into a different colloidal state. While in the first case symmetry breaking follows a standard linear instability, the second case turns out to be more complex. Depending on the dissolution pathway, there is either an intrinsically nonlinear instability, or no symmetry breaking at all (and hence no locomotion).
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Affiliation(s)
- Stephan Herminghaus
- Max-Planck Institute for Dynamics and Self-Organization, Göttingen, Germany.
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Ban T, Tani K, Nakata H, Okano Y. Self-propelled droplets for extracting rare-earth metal ions. SOFT MATTER 2014; 10:6316-6320. [PMID: 25029997 DOI: 10.1039/c4sm01001a] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We have developed self-propelled droplets having the abilities to detect a chemical gradient, to move toward a higher concentration of a specific metal ion (particularly the dysprosium ion), and to extract it. Such abilities rely on the high surface activity of di(2-ethylhexyl) phosphoric acid (DEHPA) in response to pH and the affinity of DEHPA for the dysprosium ion. We used two external stimuli as chemical signals to control droplet motion: a pH signal to induce motility and metal ions to induce directional sensing. The oil droplets loaded with DEHPA spontaneously move around beyond the threshold of pH even in a homogeneous pH field. In the presence of a gel block containing metal ions, the droplets show directional sensing and their motility is biased toward higher concentrations. The metal ions investigated can be arranged in decreasing order of directional sensing as Dy(3+)≫ Nd(3+) > Y(3+) > Gd(3+). Furthermore, the analysis of components by using an atomic absorption spectrophotometer reveals that the metal ions can be extracted from the environmental media to the interiors of the droplets. This system may offer alternative self-propelled nano/microscale machines to bubble thrust engines powered by asymmetrical catalysts.
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Affiliation(s)
- Takahiko Ban
- Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Machikaneyamacho 1-3, Toyonaka City, Osaka 560-8531, Japan.
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Suematsu NJ, Sasaki T, Nakata S, Kitahata H. Quantitative estimation of the parameters for self-motion driven by difference in surface tension. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:8101-8108. [PMID: 24934964 DOI: 10.1021/la501628d] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Quantitative information on the parameters associated with self-propelled objects would enhance the potential of this research field; for example, finding a realistic way to develop a functional self-propelled object and quantitative understanding of the mechanism of self-motion. We therefore estimated five main parameters, including the driving force, of a camphor boat as a simple self-propelled object that spontaneously moves on water due to difference in surface tension. The experimental results and mathematical model indicated that the camphor boat generated a driving force of 4.2 μN, which corresponds to a difference in surface tension of 1.1 mN m(-1). The methods used in this study are not restricted to evaluate the parameters of self-motion of a camphor boat, but can be applied to other self-propelled objects driven by difference in surface tension. Thus, our investigation provides a novel method to quantitatively estimate the parameters for self-propelled objects driven by the interfacial tension difference.
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Affiliation(s)
- Nobuhiko J Suematsu
- Graduate School of Advanced Mathematical Sciences, Meiji University , 4-21-1 Nakano, Tokyo 164-8525, Japan
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Miura S, Banno T, Tonooka T, Osaki T, Takeuchi S, Toyota T. pH-induced motion control of self-propelled oil droplets using a hydrolyzable gemini cationic surfactant. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:7977-7985. [PMID: 24934718 DOI: 10.1021/la5018032] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Self-propelled motion of micrometer-sized substances has drawn much attention as an autonomous transportation system. One candidate vehicle is a chemically driven micrometer-sized oil droplet. However, to the best of our knowledge, there has been no report of a chemical reaction system controlling the three-dimensional motion of oil droplets underwater. In this study, we developed a molecular system that controlled the self-propelled motion of 4-heptyloxybenzaldehyde oil droplets by using novel gemini cationic surfactants containing carbonate linkages (2G12C). We found that, in emulsions containing sodium hydroxide, the motion time of the self-propelled oil droplets was longer in the presence of 2G12C than in the presence of gemini cationic surfactants without carbonate linkages. Moreover, in 2G12C solution, oil droplets at rest underwent unidirectional, self-propelled motion in a gradient field toward a higher concentration of sodium hydroxide. Even though they stopped within several seconds, they restarted in the same direction. 2G12C was gradually hydrolyzed under basic conditions to produce a pair of the corresponding monomeric surfactants, which exhibit different interfacial properties from 2G12C. The prolonged and restart motion of the oil droplets were explained by the increase in the heterogeneity of the interfacial tension of the oil droplets.
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Affiliation(s)
- Shingo Miura
- Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo , 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
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Toyota T, Banno T, Nitta S, Takinoue M, Nomoto T, Natsume Y, Matsumura S, Fujinami M. Molecular Building Blocks and Their Architecture in Biologically/Environmentally Compatible Soft Matter Chemical Machinery. J Oleo Sci 2014; 63:1085-98. [DOI: 10.5650/jos.ess14190] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Banno T, Miura S, Kuroha R, Toyota T. Mode changes associated with oil droplet movement in solutions of gemini cationic surfactants. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:7689-7696. [PMID: 23706080 DOI: 10.1021/la401416h] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Micrometer-sized self-propelled oil droplets in nonequilibrium systems have attracted much attention, since they form stable emulsions composed of oil, water, and surfactant which represent a primitive type of inanimate chemical machinery. In this work, we examined means of controlling the movement of oil droplets by studying the dynamics of n-heptyloxybenzaldehyde droplets in phosphate buffers containing alkanediyl-α,ω-bis(N-dodecyl-N,N-dimethylammonium bromide) (nG12) with either tetramethylene (4G12), octaethylene (8G12), or dodecamethylene (12G12) chains in the linker moiety. Significant differences in droplet dynamics were observed to be induced by changes in the linker structure of these gemini cationic surfactants. In a phosphate buffer containing 30 mM 4G12, self-propelled motion of droplets concurrent with the formation of molecular aggregates on their surfaces was observed, whereas the fusion of oil droplets was evident in both 8G12 and 12G12 solutions. We also determined that the surface activities and the extent of molecular self-assembly of the surfactants in phosphate buffer were strongly influenced by the alkyl chain length in the linker moiety. We therefore conclude that the surface activities of the gemini cationic surfactant have important effects on the oil-water interfacial tension of oil droplets and the formation of molecular aggregates and that both of these factors induce the unique movement of the droplets.
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Affiliation(s)
- Taisuke Banno
- Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
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Ban T, Yamagami T, Nakata H, Okano Y. pH-dependent motion of self-propelled droplets due to Marangoni effect at neutral pH. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:2554-2561. [PMID: 23369012 DOI: 10.1021/la3047164] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Oil droplets loaded with surfactant propel themselves with a velocity up to 6 mm s(-1) when they are placed in an aqueous phase of NaOH solution or buffer solution. The required driving force for such motion is generated on the interface of the droplets by the change in interfacial tension, due to deprotonation of the surfactant. This force induces Marangoni convection, which gives rise to a circulating flow inside the droplets. The droplets begin to move when the axis of this circulation deviates from the vertical line. This motion depends on the pH condition of the aqueous phase. When the initial value of pH is adjusted such that the pH exceeds the threshold at the equilibrium state, the droplets move spontaneously. It was seen that the droplets were independent of the material of the solid substrates because the droplets were not directly in contact with the surface of the substrate. The condition for the onset of this spontaneous motion was verified by comparing the prediction from the linear stability analysis with experiments. The stability analysis overestimates the value of the driving force, causing instability.
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Affiliation(s)
- Takahiko Ban
- Division of Chemical Engineering, Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
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Nanzai B, Ishikawa R, Igawa M. Spontaneous Motion of o-Toluidine Droplets: Repetitive Motion of Running and Squashing. CHEM LETT 2012. [DOI: 10.1246/cl.2012.609] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Ben Nanzai
- Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University
| | - Ryotaro Ishikawa
- Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University
| | - Manabu Igawa
- Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University
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