1
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Braun F, Wagner MFP, Toimil-Molares ME, von Klitzing R. Comparison of Different Preparation Techniques of Thermophoretic Swimmers and Their Propulsion Velocity. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:5606-5616. [PMID: 38501265 DOI: 10.1021/acs.langmuir.3c01776] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/20/2024]
Abstract
The motion of partly gold (Au)-coated Janus particles under laser irradiation is caused by self-thermophoresis. Despite numerous studies addressing this topic, the impact of the preparation method and the degree of coverage of the particle with Au on the resulting thermophoretic velocity has not yet been fully understood. A detailed understanding of the most important tuning parameters during the preparation process is crucial to design Janus particles that are optimized for Au coverage to receive a high thermophoretic velocity. In this study, we explore the influence of the fabrication process, which changes the Au cap size, on the resulting self-propulsion behavior of partly Au-coated polystyrene particles (Au-PS). Additionally, the impact of an underlying adhesion chromium layer is investigated. In addition to the most commonly used qualitative SEM and EDX measurements, we propose a novel and fast technique utilizing AFM studies to quantify the cap size. This non-invasive technique can be used to determine both the size and the maximum thickness of the Au cap. The Au cap size was systematically varied in a range between about 36 and 74% by different preparation strategies. Nevertheless, we showed that the differing Au cap sizes of the Janus particles in this range have no obvious effect on the thermophoretic velocity. This is a surprising result since one would expect an effect of the Au cap size due to different solvent flows around the Janus particles and is attributed to an additional torque near the surface of the measuring cell.
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Affiliation(s)
- Franziska Braun
- Soft Matter at Interfaces, Institute for Condensed Matter Physics, Technische Universität Darmstadt, 64289 Darmstadt, Germany
| | | | | | - Regine von Klitzing
- Soft Matter at Interfaces, Institute for Condensed Matter Physics, Technische Universität Darmstadt, 64289 Darmstadt, Germany
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2
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Kalil MA, Baumgartner NR, Issa MW, Ryan SD, Wirth CL. Influence of PEG on the clustering of active Janus colloids. Colloids Surf A Physicochem Eng Asp 2021. [DOI: 10.1016/j.colsurfa.2021.127191] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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3
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Lyu X, Liu X, Zhou C, Duan S, Xu P, Dai J, Chen X, Peng Y, Cui D, Tang J, Ma X, Wang W. Active, Yet Little Mobility: Asymmetric Decomposition of H 2O 2 Is Not Sufficient in Propelling Catalytic Micromotors. J Am Chem Soc 2021; 143:12154-12164. [PMID: 34339185 DOI: 10.1021/jacs.1c04501] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
A popular principle in designing chemical micromachines is to take advantage of asymmetric chemical reactions such as the catalytic decomposition of H2O2. Contrary to intuition, we use Janus micromotors half-coated with platinum (Pt) or catalase as an example to show that this ingredient is not sufficient in powering a micromotor into self-propulsion. In particular, by annealing a thin Pt film on a SiO2 microsphere, the resulting microsphere half-decorated with discrete Pt nanoparticles swims ∼80% more slowly than its unannealed counterpart in H2O2, even though they both catalytically produce comparable amounts of oxygen. Similarly, SiO2 microspheres half-functionalized with the enzyme catalase show negligible self-propulsion despite high catalytic activity toward decomposing H2O2. In addition to highlighting how surface morphology of a catalytic cap enables/disables a chemical micromotor, this study offers a refreshed perspective in understanding how chemistry powers nano- and microscopic objects (or not): our results are consistent with a self-electrophoresis mechanism that emphasizes the electrochemical decomposition of H2O2 over nonelectrochemical pathways. More broadly, our finding is a critical piece of the puzzle in understanding and designing nano- and micromachines, in developing capable model systems of active colloids, and in relating enzymes to active matter.
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Affiliation(s)
- Xianglong Lyu
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Xiaoxia Liu
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China.,Sauvage Laboratory for Smart Materials, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China
| | - Chao Zhou
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Shifang Duan
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Pengzhao Xu
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Jia Dai
- Department of Chemistry, The University of Hong Kong, Hong Kong 999077, China
| | - Xiaowen Chen
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Yixin Peng
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Donghao Cui
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
| | - Jinyao Tang
- Department of Chemistry, The University of Hong Kong, Hong Kong 999077, China.,State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Hong Kong 999077, China
| | - Xing Ma
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China.,Sauvage Laboratory for Smart Materials, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China.,Shenzhen Bay Laboratory, No. 9 Duxue Road, Shenzhen 518055, China
| | - Wei Wang
- School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055, China
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4
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Rajupet S, Rashidi A, Wirth CL. Derjaguin-Landau-Verwey-Overbeek energy landscape of a Janus particle with a nonuniform cap. Phys Rev E 2021; 103:032610. [PMID: 33862750 DOI: 10.1103/physreve.103.032610] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Accepted: 03/08/2021] [Indexed: 01/09/2023]
Abstract
A colloidal particle is often termed "Janus" when some portion of its surface is coated by a second material which has distinct properties from the native particle. The anisotropy of Janus particles enables unique behavior at interfaces. However, rigorous methodologies to predict Janus particle dynamics at interfaces are required to implement these particles in complex fluid applications. Previous work studying Janus particle dynamics does not consider van der Waals interactions and realistic, nonuniform coating morphology. Here we develop semianalytic equations to accurately calculate the potential landscape, including van der Waals interactions, of a Janus particle with nonuniform coating thickness above a solid boundary. The effects of both nonuniform coating thickness and van der Waals interactions significantly influence the potential landscape of the particle, particularly in high ionic strength solutions, where the particle samples positions very close to the solid boundary. The equations developed herein facilitate more simple, accurate, and less computationally expensive characterization of conservative interactions experienced by a confined Janus particle than previous methods.
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Affiliation(s)
- Siddharth Rajupet
- Department of Chemical and Biomolecular Engineering, Case School of Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA
| | - Aidin Rashidi
- Department of Chemical and Biomolecular Engineering, Case School of Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA
| | - Christopher L Wirth
- Department of Chemical and Biomolecular Engineering, Case School of Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA
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5
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Duan Y, Zhao X, Sun M, Hao H. Research Advances in the Synthesis, Application, Assembly, and Calculation of Janus Materials. Ind Eng Chem Res 2021. [DOI: 10.1021/acs.iecr.0c04304] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
| | - Xia Zhao
- School of Chemical Engineering, Northwest University, Xi’an 710069, Shan xi, China
| | - Miaomiao Sun
- School of Chemical Engineering, Northwest University, Xi’an 710069, Shan xi, China
| | - Hong Hao
- School of Chemical Engineering, Northwest University, Xi’an 710069, Shan xi, China
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6
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Das S, Jalilvand Z, Popescu MN, Uspal WE, Dietrich S, Kretzschmar I. Floor- or Ceiling-Sliding for Chemically Active, Gyrotactic, Sedimenting Janus Particles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:7133-7147. [PMID: 31986887 PMCID: PMC7331144 DOI: 10.1021/acs.langmuir.9b03696] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2019] [Revised: 01/27/2020] [Indexed: 05/18/2023]
Abstract
Chemically active particles achieve motility without external forces and torques ("self-propulsion") due to catalytic chemical reactions at their surfaces, which change the chemical composition of the surrounding solution (called "chemical field") and induce hydrodynamic flow of the solution. By coupling the distortions of these fields back to its motion, a chemically active particle experiences an effective interaction with confining surfaces. This coupling can lead to a rich behavior, such as the occurrence of wall-bound steady states of "sliding". Most active particles are density mismatched with the solution and, thus, tend to sediment. Moreover, the often employed Janus spheres, which consist of an inert core material decorated with a cap-like, thin layer of a catalyst, are gyrotactic (i.e., "bottom-heavy"). Whether or not they may exhibit sliding states at horizontal walls depends on the interplay between the active motion and the gravity-driven sedimentation and alignment, such as the gyrotactic tendency to align the axis along the gravity direction being overcome by a competing, activity-driven alignment with a different orientation. It is therefore important to understand and quantify the influence of these gravity-induced effects on the behavior of model chemically active particles moving in the vicinity of walls. For model gyrotactic, self-phoretic Janus particles, here we study theoretically the occurrence of sliding states at horizontal planar walls that are either below ("floor") or above ("ceiling") the particle. We construct "state diagrams" characterizing the occurrence of such states as a function of the sedimentation velocity and of the gyrotactic response of the particle, as well as of the phoretic mobility of the particle. We show that in certain cases sliding states may emerge simultaneously at both the ceiling and the floor, while the larger part of the experimentally relevant parameter space corresponds to particles that would exhibit sliding states only either at the floor or at the ceiling-or there are no sliding states at all. These predictions are critically compared with the results of previous experimental studies, as well as with our dedicated experiments carried out with Pt-coated, polystyrene-core, or silica-core Janus spheres immersed in aqueous hydrogen peroxide solutions.
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Affiliation(s)
- Sayan Das
- Max-Planck-Institut
für Intelligente Systeme, Heisenbergstr. 3, D-70569 Stuttgart, Germany
| | - Zohreh Jalilvand
- Department
of Chemical Engineering, City College of
the City University of New York (CUNY), 140th Street and Convent Avenue, New York, New York 10031, United States
| | - Mihail N. Popescu
- Max-Planck-Institut
für Intelligente Systeme, Heisenbergstr. 3, D-70569 Stuttgart, Germany
| | - William E. Uspal
- Department
of Mechanical Engineering, University of
Hawai’i at Ma̅noa, 2540 Dole Street, Holmes Hall
302, Honolulu, Hawai’i 96822, United States
| | - Siegfried Dietrich
- Max-Planck-Institut
für Intelligente Systeme, Heisenbergstr. 3, D-70569 Stuttgart, Germany
- IV.
Institut für Theoretische
Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany
| | - Ilona Kretzschmar
- Department
of Chemical Engineering, City College of
the City University of New York (CUNY), 140th Street and Convent Avenue, New York, New York 10031, United States
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7
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Jalilvand Z, Haider H, Cui J, Kretzschmar AI. Pt-SiO 2 Janus Particles and the Water/Oil Interface: A Competition between Motility and Thermodynamics. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:6880-6887. [PMID: 32050073 DOI: 10.1021/acs.langmuir.9b03454] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Various aspects of the behavior of Janus particles near liquid/liquid interfaces have been studied through different experimental and theoretical realizations, but the effect of motility on the behavior of Janus particles near liquid/liquid interfaces has not been investigated, yet. Here, we demonstrate the ability to engineer the behavior of highly interfacial active Janus particles near a water/oil interface by introducing motility to the system. Passive, i.e., nonmotile, platinum-capped 8 μm silica (Pt-SiO2) Janus particles exhibit a strong tendency to attach to water/oil interfaces with the Pt-cap facing the oil and the SiO2 side facing the water phase. In contrast, we show that active, i.e., motile, 8 μm Pt-SiO2 Janus particles approach the interface, orient in a sideways fashion with the Janus boundary perpendicular to the interface, and then swim in the vicinity of the interface similar to observations reported near solid/liquid interfaces. Active Pt-SiO2 Janus particles near the water/oil interface show motility as a result of adding H2O2 to the particle solution. The decomposition of H2O2 into O2 and H2O creates a nonuniform gradient of O2 around the particle that hydrodynamically interacts with the water/decalin boundary. The interaction enables rotation of the particle within the swimming plane that is parallel to the interface but restricts rotation in and out of the swimming plane, thereby preventing adsorption to the liquid/liquid interface.
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Affiliation(s)
- Zohreh Jalilvand
- Department of Chemical Engineering, The City College of New York, New York , New York 10031, United States
| | - Hamad Haider
- Department of Chemical Engineering, The City College of New York, New York , New York 10031, United States
| | - Jingqin Cui
- Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen, Fujian 361005, PR China
| | - And Ilona Kretzschmar
- Department of Chemical Engineering, The City College of New York, New York , New York 10031, United States
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8
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Popescu MN. Chemically Active Particles: From One to Few on the Way to Many. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:6861-6870. [PMID: 32233489 PMCID: PMC7331135 DOI: 10.1021/acs.langmuir.9b03973] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2019] [Revised: 04/01/2020] [Indexed: 06/01/2023]
Abstract
Chemically active particles suspended in a liquid solution can achieve self-motility by locally changing the chemical composition of the solution via catalytic reactions at their surfaces. They operate intrinsically out of equilibrium, continuously extracting free energy from the environment to power the dissipative self-motility. The effective interactions involving active particles are, in general, nonreciprocal and anisotropic, even if the particles have simple shapes (e.g., Janus spheres). Accordingly, for chemically active particles a very rich behavior of collective motion and self-assembly may be expected to emerge, including phenomena such as microphase separation in the form of kinetically stable, finite-sized aggregates. Here, I succinctly review a number of recent experimental studies that demonstrate the self-assembly of structures, involving chemically active Janus particles, which exhibit various patterns of motion. These examples illustrate concepts such as "motors made out of motors" (as suggestively named by Fischer [Fischer, P. Nat. Phys. 2018, 14, 1072]). The dynamics of assembly and structure formation observed in these systems can provide benchmark, in-depth testing of the current understanding of motion and effective interactions produced by chemical activity. Finally, one notes that these significant achievements are likely just the beginning of the field. Recently reported particles endowed with time-dependent chemical activity or switchable reaction mechanisms open the way for exciting developments, such as periodic reshaping of self-assembled structures based on man-made internal clocks.
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9
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Rashidi A, Razavi S, Wirth CL. Influence of cap weight on the motion of a Janus particle very near a wall. Phys Rev E 2020; 101:042606. [PMID: 32422805 DOI: 10.1103/physreve.101.042606] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Accepted: 03/20/2020] [Indexed: 12/26/2022]
Abstract
The dynamics of anisotropic nano- to micro scale colloidal particles in confined environments, either near neighboring particles or boundaries, is relevant to a wide range of applications. We utilized Brownian dynamics simulations to predict the translational and rotational fluctuations of a Janus sphere with a cap of nonmatching density near a boundary. The presence of the cap significantly impacted the rotational dynamics of the particle as a consequence of gravitational torque at experimentally relevant conditions. Gravitational torque dominated stochastic torque for a particle >1 μm in diameter and with a 20-nm-thick gold cap. Janus particles at these conditions sampled mostly cap-down or "quenched" orientations. Although the results summarized herein showed that particles of smaller diameter (<1 μm) with a thin gold coating (<5 nm) behave similarly to an isotropic particle, small increases in either particle diameter or coating thickness quenched the polar rotation of the particle. Histogram landscapes of the separation distance from the boundary and orientation observations of particles with larger diameters or thicker gold coatings were mostly populated with quenched configurations. Finally, the histogram landscapes were inverted to obtain the potential energy landscapes, providing a road map for experimental data to be interpreted.
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Affiliation(s)
- Aidin Rashidi
- Chemical and Biomedical Engineering Department, Washkewicz College of Engineering, Cleveland State University, 2121 Euclid Avenue, Cleveland, Ohio 44115, USA
| | - Sepideh Razavi
- Chemical, Biological, and Materials Engineering Department, University of Oklahoma, Norman, Oklahoma 73019, USA
| | - Christopher L Wirth
- Chemical and Biomedical Engineering Department, Washkewicz College of Engineering, Cleveland State University, 2121 Euclid Avenue, Cleveland, Ohio 44115, USA
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10
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Knapp EM, Dagastine RR, Tu RS, Kretzschmar I. Effect of Orientation and Wetting Properties on the Behavior of Janus Particles at the Air-Water Interface. ACS APPLIED MATERIALS & INTERFACES 2020; 12:5128-5135. [PMID: 31885259 DOI: 10.1021/acsami.9b21067] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The adhesion force and contact angle of gold-capped silica Janus particles and plain silica particles at an air-water interface are studied via colloidal atomic force microscopy. Particles are attached to cantilevers at various orientations, and wetting properties of the gold surface are varied through modification with dodecanethiol. Thiol modification increases the hydrophobicity of the gold surface, thereby increasing the difference between the contact angles of the gold hemisphere and the silica hemisphere and, thus, increasing the degree of amphiphilicity of the Janus particle. Subsequently, the colloidal probe is pushed into a stationary bubble from the water phase followed by retraction back into the water phase. Adhesion force is found to be higher for Janus particles than isotropic silica particles, regardless of orientation of the anisotropic hemisphere. Particles with their polar half oriented toward the water and apolar half facing the air show an increase in adhesion force and contact angle as the degree of amphiphilicity of the particles increases. For particles of the reverse orientation, no significant difference is observed as wetting properties change. Both adhesion force and contact angle display an inverse relationship with a cap angle for particles with a higher degree of amphiphilicity. These results are of importance for using Janus particles to stabilize interfaces as well as for understanding the equilibrium height of Janus particles at the interface, which will impact capillary interactions and thus self-assembly.
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Affiliation(s)
- Ellen M Knapp
- Department of Chemical Engineering , The City College of New York , New York 10031 , United States
- Department of Chemical Engineering and the Particulate Fluids Processing Centre , University of Melbourne , Parkville 3010 , Australia
| | - Raymond R Dagastine
- Department of Chemical Engineering and the Particulate Fluids Processing Centre , University of Melbourne , Parkville 3010 , Australia
| | - Raymond S Tu
- Department of Chemical Engineering , The City College of New York , New York 10031 , United States
| | - Ilona Kretzschmar
- Department of Chemical Engineering , The City College of New York , New York 10031 , United States
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11
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Razavi S, Lin B, Lee KYC, Tu RS, Kretzschmar I. Impact of Surface Amphiphilicity on the Interfacial Behavior of Janus Particle Layers under Compression. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:15813-15824. [PMID: 31269790 DOI: 10.1021/acs.langmuir.9b01664] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Langmuir monolayers of silica/gold Janus particles with two different degrees of amphiphilicity have been examined to study the significance of particle surface amphiphilicity on the structure and mechanical properties of the interfacial layers. The response of the layers to the applied compression provides insight into the nature and strength of the interparticle interactions. Different collapse modes observed for the interfacial layers are linked to the amphiphilicity of Janus particles and their configuration at the interface. Molecular dynamics simulations on nanoparticles with similar contact angles provide insight on the arrangement of particles at the interface and support our conclusion that the interfacial configuration and collapse of anisotropic particles at the air/water interface are controlled by particle amphiphilicity.
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Affiliation(s)
- Sepideh Razavi
- Chemical, Biological, and Materials Engineering , University of Oklahoma , Norman , Oklahoma 73019 , United States
| | | | | | - Raymond S Tu
- Department of Chemical Engineering , City College of the City University of New York , New York , New York 10031 , United States
| | - Ilona Kretzschmar
- Department of Chemical Engineering , City College of the City University of New York , New York , New York 10031 , United States
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12
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Vatankhah Z, Dehghani E, Salami-Kalajahi M, Roghani-Mamaqani H. One-step fabrication of low cytotoxic anisotropic poly(2-hydroxyethyl methacrylate-co-methacrylic acid) particles for efficient release of DOX. J Drug Deliv Sci Technol 2019. [DOI: 10.1016/j.jddst.2019.101332] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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13
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Issa M, Baumgartner NR, Kalil MA, Ryan SD, Wirth CL. Charged Nanoparticles Quench the Propulsion of Active Janus Colloids. ACS OMEGA 2019; 4:13034-13041. [PMID: 31460430 PMCID: PMC6705040 DOI: 10.1021/acsomega.9b00765] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Accepted: 07/25/2019] [Indexed: 06/10/2023]
Abstract
Active colloidal particles regularly interact with surfaces in applications ranging from microfluidics to sensing. Recent work has revealed the complex nature of these surface interactions for active particles. Herein, we summarize experiments and simulations that show the impact of charged nanoparticles on the propulsion of an active colloid near a boundary. Adding charged nanoparticles not only decreased the average separation distance of a passive colloid because of depletion attraction as expected but also decreased the apparent propulsion of a Janus colloid to near zero. Complementary agent-based simulations considering the impact of hydrodynamics for active Janus colloids were conducted in the range of separation distances inferred from experiment. These simulations showed that propulsion speed decreased monotonically with decreasing average separation distance. Although the trend found in experiments and simulations was in qualitative agreement, there was still a significant difference in the magnitude of speed reduction. The quantitative difference was attributed to the influence of charged nanoparticles on the conductivity of the active particle suspension. Follow-up experiments delineating the impact of depletion and conductivity showed that both contribute to the reduction of speed for an active Janus particle. The experimental and simulated data suggests that it is necessary to consider the synergistic effects between various mechanisms influencing interactions experienced by an active particle near a boundary.
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Affiliation(s)
- Marola
W. Issa
- Department
of Chemical and Biomedical Engineering, Washkewicz College
of Engineering and Department of Mathematics and Statistics, College of Science and
Health Professions, Cleveland State University, 2121 Euclid Avenue, Cleveland, Ohio 44115, United States
| | - Nicky R. Baumgartner
- Department
of Chemical and Biomedical Engineering, Washkewicz College
of Engineering and Department of Mathematics and Statistics, College of Science and
Health Professions, Cleveland State University, 2121 Euclid Avenue, Cleveland, Ohio 44115, United States
| | - Mohammed A. Kalil
- Department
of Chemical and Biomedical Engineering, Washkewicz College
of Engineering and Department of Mathematics and Statistics, College of Science and
Health Professions, Cleveland State University, 2121 Euclid Avenue, Cleveland, Ohio 44115, United States
| | - Shawn D. Ryan
- Department
of Chemical and Biomedical Engineering, Washkewicz College
of Engineering and Department of Mathematics and Statistics, College of Science and
Health Professions, Cleveland State University, 2121 Euclid Avenue, Cleveland, Ohio 44115, United States
| | - Christopher L. Wirth
- Department
of Chemical and Biomedical Engineering, Washkewicz College
of Engineering and Department of Mathematics and Statistics, College of Science and
Health Professions, Cleveland State University, 2121 Euclid Avenue, Cleveland, Ohio 44115, United States
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