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Kurimský J, Rajňák M, Paulovičová K, Šárpataky M. Electric partial discharges in biodegradable oil-based ferrofluids: A study on effects of magnetic field and nanoparticle concentration. Heliyon 2024; 10:e29259. [PMID: 38623215 PMCID: PMC11016718 DOI: 10.1016/j.heliyon.2024.e29259] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 03/18/2024] [Accepted: 04/03/2024] [Indexed: 04/17/2024] Open
Abstract
This paper presents an experimental study of partial discharge activity in ferrofluids based on biodegradable transformer oil and iron oxide nanoparticles. Three ferrofluid samples with low, medium and high nanoparticle concentrations are employed in the research. The basic ferrofluid characterization is followed by a partial discharge experiment exposing the ferrofluids to a high voltage in a needle-plate electrode configuration. The analysis confirms that the apparent charge and number of discharges decrease with increasing nanoparticle concentration. These findings are interpreted with reference to the well-recognised electro-hydrodynamic streamer model. The charge trapping by nanoparticles hinders the ionization and discharge development. The study also focuses on the partial discharge activity in the ferrofluids under the action of a static magnetic field acting perpendicularly to the electric field. A decreasing trend in the number of discharges due to the magnetic field is revealed. A qualitative explanation is provided based on the field-induced cluster formation and charge mobility reduction. The presented experiment and the discussed findings may be valuable for practical application of the ferrofluid in high voltage equipment with a special need for partial discharge suppression.
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Affiliation(s)
- Juraj Kurimský
- Faculty of Electrical Engineering and Informatics, Technical University of Košice, Letná 9, 04200, Košice, Slovakia
| | - Michal Rajňák
- Faculty of Electrical Engineering and Informatics, Technical University of Košice, Letná 9, 04200, Košice, Slovakia
- Institute of Experimental Physics SAS, Watsonova 47, 04001, Košice, Slovakia
| | | | - Miloš Šárpataky
- Faculty of Electrical Engineering and Informatics, Technical University of Košice, Letná 9, 04200, Košice, Slovakia
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2
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Philip J. Magnetic nanofluids (Ferrofluids): Recent advances, applications, challenges, and future directions. Adv Colloid Interface Sci 2023; 311:102810. [PMID: 36417827 DOI: 10.1016/j.cis.2022.102810] [Citation(s) in RCA: 16] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Revised: 10/28/2022] [Accepted: 11/05/2022] [Indexed: 11/16/2022]
Abstract
Impelled by the need to find solutions to new challenges of modern technologies new materials with unique properties are being explored. Among various new materials that emerged over the decades, magnetic fluids exhibiting interesting physiochemical properties (optical, thermal, magnetic, rheological, apparent density, etc.) under a magnetic stimulus have been at the forefront of research. In the initial phase, there has been a fervent scientific curiosity to understand the field-induced intriguing properties of such fluids but later a plethora of technological applications emerged. Magnetic nanofluid, popularly known as ferrofluid, is a colloidal suspension of fine magnetic nanoparticles, has been at the forefront of research because of its magnetically tunable physicochemical properties and applications. Due to their stimuli-responsive behaviour, they have been finding more applications in biology and other engineering disciplines in recent years. Therefore, a critical review of this topic highlighting the necessary background, the potential of this material for emerging technologies, and the latest developments is warranted. This review also provides a summary of various applications, along with the key challenges and future research directions. The first part of the review addresses the different types of magnetic fluids, the genesis of magnetic fluids, their synthesis methodologies, properties, and stabilization techniques are discussed in detail. The second part of the review highlights the applications of magnetic nanofluids and nanoemulsions (as model systems) in probing order-disorder transitions, scattering, diffraction, magnetically reconfigurable internal structures, molecular interaction, and weak forces between colloidal particles, conformational changes of macromolecules at interfaces and polymer-surfactant complexation at the oil-water interface. The last part of the review summarizes the interesting applications of magnetic fluids such as heat transfer, sensors (temperature, pH, urea detection, cations, defect detection sensors), tunable optical filters, removal of dyes, dynamic seals, magnetic hyperthermia-based cancer therapy and other biomedical applications. The applications of magnetic nanofluids in diverse disciplines are growing day by day, yet there are challenges in their practical adaptation as field-worthy or packaged products. This review provides a pedagogical description of magnetic fluids, with the necessary background, key concepts, physics, experimental protocols, design of experiments, challenges and future directions.
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Affiliation(s)
- John Philip
- Smart Materials Section, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, India.
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3
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Upadhyay RV, Raj K, Parekh KH, Pisuwala MS, Jadav MH. The viscous response of ferrofluids subjected to external magnetic field. J DISPER SCI TECHNOL 2022. [DOI: 10.1080/01932691.2022.2106997] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
Affiliation(s)
- R. V. Upadhyay
- Dr. K C Patel Research & Development Center, Charotar University of Science &Technology, Changa, Gujarat, India
| | - K. Raj
- Dr. K C Patel Research & Development Center, Charotar University of Science &Technology, Changa, Gujarat, India
| | - Kinnari H. Parekh
- Dr. K C Patel Research & Development Center, Charotar University of Science &Technology, Changa, Gujarat, India
| | - Mujiba S. Pisuwala
- Dr. K C Patel Research & Development Center, Charotar University of Science &Technology, Changa, Gujarat, India
| | - Mudra H. Jadav
- Dr. K C Patel Research & Development Center, Charotar University of Science &Technology, Changa, Gujarat, India
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4
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Socoliuc V, Avdeev MV, Kuncser V, Turcu R, Tombácz E, Vékás L. Ferrofluids and bio-ferrofluids: looking back and stepping forward. NANOSCALE 2022; 14:4786-4886. [PMID: 35297919 DOI: 10.1039/d1nr05841j] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Ferrofluids investigated along for about five decades are ultrastable colloidal suspensions of magnetic nanoparticles, which manifest simultaneously fluid and magnetic properties. Their magnetically controllable and tunable feature proved to be from the beginning an extremely fertile ground for a wide range of engineering applications. More recently, biocompatible ferrofluids attracted huge interest and produced a considerable increase of the applicative potential in nanomedicine, biotechnology and environmental protection. This paper offers a brief overview of the most relevant early results and a comprehensive description of recent achievements in ferrofluid synthesis, advanced characterization, as well as the governing equations of ferrohydrodynamics, the most important interfacial phenomena and the flow properties. Finally, it provides an overview of recent advances in tunable and adaptive multifunctional materials derived from ferrofluids and a detailed presentation of the recent progress of applications in the field of sensors and actuators, ferrofluid-driven assembly and manipulation, droplet technology, including droplet generation and control, mechanical actuation, liquid computing and robotics.
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Affiliation(s)
- V Socoliuc
- Romanian Academy - Timisoara Branch, Center for Fundamental and Advanced Technical Research, Laboratory of Magnetic Fluids, Mihai Viteazu Ave. 24, 300223 Timisoara, Romania.
| | - M V Avdeev
- Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Joliot-Curie Str. 6, 141980 Dubna, Moscow Reg., Russia.
| | - V Kuncser
- National Institute of Materials Physics, Bucharest-Magurele, 077125, Romania
| | - Rodica Turcu
- National Institute for Research and Development of Isotopic and Molecular Technologies (INCDTIM), Donat Str. 67-103, 400293 Cluj-Napoca, Romania
| | - Etelka Tombácz
- University of Szeged, Faculty of Engineering, Department of Food Engineering, Moszkvai krt. 5-7, H-6725 Szeged, Hungary.
- University of Pannonia - Soós Ernő Water Technology Research and Development Center, H-8800 Zrínyi M. str. 18, Nagykanizsa, Hungary
| | - L Vékás
- Romanian Academy - Timisoara Branch, Center for Fundamental and Advanced Technical Research, Laboratory of Magnetic Fluids, Mihai Viteazu Ave. 24, 300223 Timisoara, Romania.
- Politehnica University of Timisoara, Research Center for Complex Fluids Systems Engineering, Mihai Viteazul Ave. 1, 300222 Timisoara, Romania
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5
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Mohapatra DK, Camp PJ, Philip J. Influence of size polydispersity on magnetic field tunable structures in magnetic nanofluids containing superparamagnetic nanoparticles. NANOSCALE ADVANCES 2021; 3:3573-3592. [PMID: 36133709 PMCID: PMC9419785 DOI: 10.1039/d1na00131k] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Accepted: 04/23/2021] [Indexed: 06/01/2023]
Abstract
We probe the influence of particle size polydispersity on field-induced structures and structural transitions in magnetic fluids (ferrofluids) using phase contrast optical microscopy, light scattering and Brownian dynamics simulations. Three different ferrofluids containing superparamagnetic nanoparticles of different polydispersity indices (PDIs) are used. In a ferrofluid with a high PDI (∼0.79), thin chains, thick chains, and sheets are formed on increasing the in-plane magnetic field, whereas isotropic bubbles, and hexagonal and lamellar/stripe structures are formed on increasing the out-of-plane magnetic field over the same range. In contrast, no field-induced aggregates are seen in the sample with low polydispersity under the above conditions. In a polydisperse sample, bubbles are formed at a very low magnetic field strength of 30 G. Insights into the structural evolution with increasing magnetic field strength are obtained by carrying out Brownian dynamics simulations. The crossovers from isotropic, through hexagonal columnar, to lamellar/stripe structures observed with increasing field strength in the high-polydispersity sample indicate the prominent roles of large, more strongly interacting particles in structural transitions in ferrofluids. Based on the observed microstructures, a phase diagram is constructed. Our work opens up new opportunities to develop optical devices and access diverse structures by tuning size polydispersity.
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Affiliation(s)
- Dillip Kumar Mohapatra
- Smart Materials Section, Corrosion Science and Technology Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, HBNI Kalpakkam-603102 India
| | - Philip J Camp
- School of Chemistry, University of Edinburgh David Brewster Road Edinburgh EH9 3FJ Scotland UK
- Department of Theoretical and Mathematical Physics, Institute of Natural Sciences and Mathematics, Ural Federal University 51 Lenin Avenue Ekaterinburg 620000 Russia
| | - John Philip
- Smart Materials Section, Corrosion Science and Technology Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, HBNI Kalpakkam-603102 India
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6
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van Silfhout AM, Engelkamp H, Erné BH. Colloidal Stability of Aqueous Ferrofluids at 10 T. J Phys Chem Lett 2020; 11:5908-5912. [PMID: 32627556 PMCID: PMC7467736 DOI: 10.1021/acs.jpclett.0c01804] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2020] [Accepted: 07/05/2020] [Indexed: 06/11/2023]
Abstract
Magnetic density separation is an emerging recycling technology by which several different waste materials-from plastic products, electronics, or other-can be sorted in a single continuous processing step. Larger-scale installations will require ferrofluids that remain stable at several teslas, high magnetic fields at which colloidal stability was not investigated before. Here we optically monitor the concentration profile of iron oxide nanoparticles in aqueous ferrofluids at a field of 10 T and a gradient of 100 T/m. The sedimentation velocities and equilibrium concentration profiles inform on maintenance or breakdown of colloidal stability, which depends on the concentration and magnetic coupling energy of the nanoparticles. Comparison with results obtained with a small neodymium magnet indicate that stability at moderate fields is predictive of stability at much higher fields, which facilitates the development of new ferrofluids dedicated to magnetic density separation.
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Affiliation(s)
- Alex M. van Silfhout
- Van
’t Hoff Laboratory for Physical and Colloid Chemistry, Debye
Institute for Nanomaterials Science, Utrecht
University, 3584 CH Utrecht, The Netherlands
| | - Hans Engelkamp
- High
Field Magnet Laboratory (HFML−EMFL), Radboud University Nijmegen, 6525 ED Nijmegen, The Netherlands
| | - Ben H. Erné
- Van
’t Hoff Laboratory for Physical and Colloid Chemistry, Debye
Institute for Nanomaterials Science, Utrecht
University, 3584 CH Utrecht, The Netherlands
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7
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Mohapatra DK, Laskar JM, Philip J. Temporal evolution of equilibrium and non-equilibrium magnetic field driven microstructures in a magnetic fluid. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2020.112737] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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8
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Abstract
Observing the light passing through a thin layer of ferrofluid, we can see the occurrence of interesting effects, both in the formation patterns within the ferrofluid layer and in the dispersion of light outside that layer. This leads us to ask what the explanations associated with these effects are. In this paper, we analyze and explain the occurrence of these luminous patterns using a Ferrolens, commercially known as a Ferrocell. We present details of our experimental apparatus, followed by a discussion of some properties of light polarization and its relation to the formation of magnetic contours produced by a Ferrolens. In addition, we present the observation of a magnetochiral effect in this system. Next, we propose an application of this experiment in dynamical systems. The dynamical system is the direct observation of diffracted lines in Ferrolens, a special case of a Hele-Shaw cell containing a transparent ferrofluid subjected to various light sources.
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9
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Abstract
An effective Landau-like description of ferronematics, i.e., suspensions of magnetic colloidal particles in a nematic liquid crystal (NLC), is developed in terms of the corresponding magnetization and nematic director fields. The study is based on a microscopic model and on classical density functional theory. Ferronematics are susceptible to weak magnetic fields and they can exhibit a ferromagnetic phase, which has been predicted several decades ago and has recently been found experimentally. Within the proposed effective Landau theory of ferronematics, one has quantitative access, e.g., to the coupling between the magnetization of the magnetic colloids and the nematic director of the NLC. On mesoscopic length scales, this generates complex response patterns.
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Affiliation(s)
- Grigorii Zarubin
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, 70569 Stuttgart, Germany and IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
| | - Markus Bier
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, 70569 Stuttgart, Germany and IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
| | - S Dietrich
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, 70569 Stuttgart, Germany and IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
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10
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Kuraica MM, Iskrenović P, Perić M, Krstić I, Nikolić AS. External magnetic field influence on magnetite and cobalt-ferrite nano-particles in ferrofluid. CHEMICAL PAPERS 2018. [DOI: 10.1007/s11696-017-0380-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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11
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Heinrich D, Goñi AR, Osán TM, Cerioni LMC, Smessaert A, Klapp SHL, Faraudo J, Pusiol DJ, Thomsen C. Effects of magnetic field gradients on the aggregation dynamics of colloidal magnetic nanoparticles. SOFT MATTER 2015; 11:7606-7616. [PMID: 26291429 DOI: 10.1039/c5sm00541h] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We have used low-field (1)H nuclear-magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) to investigate the aggregation dynamics of magnetic particles in ionic ferrofluids (IFFs) in the presence of magnetic field gradients. At the beginning of the experiments, the measured NMR spectra were broad and asymmetric, exhibiting two features attributed to different dynamical environments of water protons, depending on the local strength of the field gradients. Hence, the spatial redistribution of the magnetic particles in the ferrofluid caused by the presence of an external magnetic field in a time scale of minutes can be monitored in real time, following the changes in the features of the NMR spectra during a period of about an hour. As previously reported [Heinrich et al., Phys. Rev. Lett., 2011, 106, 208301], in the homogeneous magnetic field of a NMR spectrometer, the aggregation of the particles of the IFF proceeds in two stages. The first stage corresponds to the gradual aggregation of monomers prior to and during the formation of chain-like structures. The second stage proceeds after the chains have reached a critical average length, favoring lateral association of the strings into hexagonal zipped-chain superstructures or bundles. In this work, we focus on the influence of a strongly inhomogeneous magnetic field on the aforementioned aggregation dynamics. The main observation is that, as the sample is immersed in a certain magnetic field gradient and kept there for a time τinh, magnetophoresis rapidly converts the ferrofluid into an aggregation state which finds its correspondence to a state on the evolution curve of the pristine sample in a homogeneous field. From the degree of aggregation reached at the time τinh, the IFF sample just evolves thereafter in the homogeneous field of the NMR spectrometer in exactly the same way as the pristine sample. The final equilibrium state always consists of a colloidal suspension of zipped-chain bundles with the chain axes aligned along the magnetic field direction.
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Affiliation(s)
- D Heinrich
- Institut für Festkörperphysik, EW 5-4, Technische Universität Berlin, Hardenbergstrasse 36, D-10623 Berlin, Germany
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12
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Espinosa D, Carlsson LB, Neto AMF, Alves S. Influence of nanoparticle size on the nonlinear optical properties of magnetite ferrofluids. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:032302. [PMID: 24125263 DOI: 10.1103/physreve.88.032302] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2013] [Revised: 07/26/2013] [Indexed: 06/02/2023]
Abstract
The nonlinear index of refraction (n_{2}) and the two-photon absorption coefficient (β) of water-based ferrofluids made of magnetite nanocrystals of different sizes and with different coatings have been measured through the Z-scan technique, with ultrashort (femtoseconds) laser pulses. Their third-order susceptibility is calculated from the values of n_{2} and β. The influence of different particles' coatings and sizes on these nonlinear optical properties are investigated. The values of n_{2} and β depend more significantly on the nanoparticles' size than on the particular coating. We observe a decrease of β as the nanoparticles' diameters decrease, although the optical gap is found to be the same for all samples. The results are interpreted considering modifications in the electronic orbital shape due to the particles' nanosize effect.
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Affiliation(s)
- D Espinosa
- Instituto de Física, Universidade de São Paulo, Caixa Postal 66318, 05314-970 São Paulo, SP, Brazil
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13
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Richardi J, Weis JJ. Influence of short range potential on field induced chain aggregation in low density dipolar particles. J Chem Phys 2013; 138:244704. [DOI: 10.1063/1.4811290] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
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14
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XIA SIHUA, WANG JUN, LU ZHANGXIAN, ZHANG FEIYAN. BIREFRINGENCE AND MAGNETO-OPTICAL PROPERTIES IN OLEIC ACID COATED Fe3O4 NANOPARTICLES: APPLICATION FOR OPTICAL SWITCH. INTERNATIONAL JOURNAL OF NANOSCIENCE 2012. [DOI: 10.1142/s0219581x11008289] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We report magneto-optical properties in a kerosene colloidal suspension of oleic acid coated Fe3O4 nanoparticles (~14 nm). The magnetic colloids (fluids) show birefringence under a magnetic field. Systematical studies of the on–off switch times upon application of the on–off magnetic field with varied experimental parameters indicate that the switch response time depends strongly on the strength of the magnetic field and the concentration of the magnetic nanoparticles in the fluid. The data can be explained in terms of the formation of magnetic nanoparticle chains under a magnetic field. The important magneto-optical properties of the magnetic fluids allow us to design a tunable optical switch.
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Affiliation(s)
- SI-HUA XIA
- Faculty of Science, Ningbo University Ningbo, 315211, Zhejiang, China
| | - JUN WANG
- Faculty of Science, Ningbo University Ningbo, 315211, Zhejiang, China
| | - ZHANG-XIAN LU
- Junior College, Wanli University Ningbo, 315100, Zhejiang, China
| | - FEIYAN ZHANG
- Faculty of Science, Ningbo University Ningbo, 315211, Zhejiang, China
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15
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Heinrich D, Goñi AR, Smessaert A, Klapp SHL, Cerioni LMC, Osán TM, Pusiol DJ, Thomsen C. Dynamics of the field-induced formation of hexagonal zipped-chain superstructures in magnetic colloids. PHYSICAL REVIEW LETTERS 2011; 106:208301. [PMID: 21668267 DOI: 10.1103/physrevlett.106.208301] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2010] [Indexed: 05/30/2023]
Abstract
Combining nuclear magnetic resonance and molecular dynamics simulations, we unravel the long-time dynamics of a paradigmatic colloid with strong dipole-dipole interactions. In a homogeneous magnetic field, ionic ferrofluids exhibit a stepwise association process from ensembles of monomers over stringlike chains to bundles of hexagonal zipped-chain patches. We demonstrate that attractive van der Waals interactions due to charge-density fluctuations in the magnetic particles play the key role for the dynamical stabilization of the hexagonal superstructures against thermal dissociation. Our results give insight into the dynamics of self-organization in systems dominated by dipolar interactions.
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Affiliation(s)
- D Heinrich
- Institut für Festkörperphysik, EW 5-4, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany
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Laskar JM, Philip J, Raj B. Experimental investigation of magnetic-field-induced aggregation kinetics in nonaqueous ferrofluids. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 82:021402. [PMID: 20866804 DOI: 10.1103/physreve.82.021402] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2010] [Revised: 06/22/2010] [Indexed: 05/15/2023]
Abstract
We investigate the influence of field ramp rate on the kinetics of magnetic dipole-dipole induced chainlike structure formation in a nonaqueous nanoparticle dispersion using light scattering studies. With increase in magnetic field, at a constant ramp rate, the transmitted light intensity diminishes and the transmitted light spot is transformed to a diffused ring due to scattering from the self-assembled linear aggregates. The decay rate of transmitted intensity increases up to an optimum ramp rate, above which the trend becomes reverse. At an optimum ramp rate, the minimum time for initial aggregation coincides with the exposure time where the intensity decay is fastest. The variation of transmitted intensity at different ramp rate is explained on the basis of initial aggregation time that depends on Brownian motion, dipolar magnetic attraction and multibody hydrodynamic interactions. The slope of the transmitted light intensity after the removal of magnetic field depends on the time required for dissociation of ordered linear structures. Disappearance of the ring pattern and the reappearance of original light spot, upon removal of the magnetic field, confirm the perfect reversibility of the linear aggregates. The observed concentration dependant decay rates are in good agreement with aggregation theory.
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Affiliation(s)
- Junaid M Laskar
- SMARTS, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamilnadu, India
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17
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Laskar JM, Philip J, Raj B. Experimental evidence for reversible zippering of chains in magnetic nanofluids under external magnetic fields. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 80:041401. [PMID: 19905308 DOI: 10.1103/physreve.80.041401] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2009] [Revised: 08/24/2009] [Indexed: 05/28/2023]
Abstract
We study the time-dependent transmitted intensity and the scattered pattern from magnetic nanofluids at constant ramping of uniform external magnetic field. The nanofluid used is the dispersion of magnetite particles with an average diameter of 6.5 nm with a protective surfactant coating. We observe several critical fields at which the transmitted light intensity decreases drastically followed by the formation of a ringlike pattern on a screen placed perpendicular to the field direction. Interestingly, the critical fields occur at a regular interval of 20 G. The observed critical fields are attributed to zippering transitions of the chains due to attractive energy well when the chains are of different lengths or shifted with respect to one another. Interaction energy calculations show a decrease in the energy of the system due to dipolar interactions at different critical fields confirming the lowering of the system energy through lateral coalescence. The observed zippering phenomenon is perfectly reversible.
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Affiliation(s)
- Junaid M Laskar
- Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamilnadu, India
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