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Kotni R, Grau-Carbonell A, Chiappini M, Dijkstra M, van Blaaderen A. Splay-bend nematic phases of bent colloidal silica rods induced by polydispersity. Nat Commun 2022; 13:7264. [DOI: 10.1038/s41467-022-34658-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Accepted: 11/01/2022] [Indexed: 12/02/2022] Open
Abstract
AbstractLiquid crystal (LC) phases are in between solids and liquids with properties of both. Nematic LCs composed of rod-like molecules or particles exhibit long-range orientational order, yielding characteristic birefringence, but they lack positional order, allowing them to flow like a liquid. This combination of properties as well as their sensitivity to external fields make nematic LCs fundamental for optical applications e.g. liquid crystal displays (LCDs). When rod-like particles become bent, spontaneous bend deformations arise in the LC, leading to geometric frustration which can be resolved by complementary twist or splay deformations forming intriguing twist-bend (NTB) and splay-bend (NSB) nematic phases. Here, we show experimentally that the elusive NSB phases can be stabilized in systems of polydisperse micron-sized bent silica rods. Our results open avenues for the realization of NTB and NSB phases of colloidal and molecular LCs.
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2
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Seifert J, Günzing D, Webers S, Dulle M, Kruteva M, Landers J, Wende H, Schmidt AM. Strain- and field-induced anisotropy in hybrid elastomers with elongated filler nanoparticles. SOFT MATTER 2021; 17:7565-7584. [PMID: 34341807 DOI: 10.1039/d0sm02104k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The implementation of anisotropy to functional materials is a key step towards future smart materials. In this work, we evaluate the influence of preorientation and sample architecture on the strain-induced anisotropy in hybrid elastomers containing covalently attached elongated magnetic filler particles. Accordingly, silica coated spindle-type hematite nanoparticles are incorporated into poly(dimethylsiloxane)-based elastomers, and two types of composite architectures are compared: on the one hand a conventional architecture of filled, covalently crosslinked elastomers, and on the other hybrid elastomers that are crosslinked exclusively by covalent attachment of the polymer chains to the particle surface. By the application of external strain and with magnetic fields, the orientational order of the elongated nanoparticles can be manipulated, and we investigate the interplay between strain, magnetic order, and orientational order of the particles by combining 2D small angle X-ray scattering experiments under strain and fields with Mössbauer spectroscopy under similar conditions, and supplementary angular-dependent magnetization experiments. The converging information is used to quantify the order in these interesting materials, while establishing a direct link between the magnetic properties and the spatial orientation of the embedded magnetic nanoparticles.
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Affiliation(s)
- Julian Seifert
- Chemistry Department, Universität zu Köln, 50939 Köln, Germany.
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3
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Lucht N, Hinrichs S, Großmann L, Pelz C, Felgenhauer E, Clasen E, Schwenk M, Hankiewicz B. Synthesis of magnetic ferrogels: a tool-box approach for finely tuned magnetic- and temperature-dependent properties. PHYSICAL SCIENCES REVIEWS 2021. [DOI: 10.1515/psr-2019-0120] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Abstract
Multi responsive hydrogels have many potential applications in the field of medicine as well as technical fields and are of great interest in fundamental research. Here we present the synthesis and characterization of tailored magnetic hydrogels – micro- as well as macrogels – which consist of iron oxide and cobalt ferrite, varying in phase and morphology, embedded in a thermoresponsive polymer. We introduce new ways to synthesize magnetic particles and revisit some common strategies when dealing with particle synthesis. Subsequently we discuss the details of the thermoresponsive matrix and how we can influence and manipulate the thermoresponsive properties, i.e. the lower critical solution temperature. Ultimately, we present the particle-hydrogel composite and show two exemplary applications for particle matrix interactions, i.e. heat transfer and reorientation of the particles in a magnetic field.
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Affiliation(s)
- Niklas Lucht
- Institute of Physical Chemistry, Hamburg University , Grindelallee 117, 20146 Hamburg , Germany
| | - Stephan Hinrichs
- Institute of Physical Chemistry, Hamburg University , Grindelallee 117, 20146 Hamburg , Germany
| | - Larissa Großmann
- Institute of Physical Chemistry, Hamburg University , Grindelallee 117, 20146 Hamburg , Germany
| | - Catharina Pelz
- Institute of Physical Chemistry, Hamburg University , Grindelallee 117, 20146 Hamburg , Germany
| | - Elena Felgenhauer
- Institute of Physical Chemistry, Hamburg University , Grindelallee 117, 20146 Hamburg , Germany
| | - Eike Clasen
- Institute of Physical Chemistry, Hamburg University , Grindelallee 117, 20146 Hamburg , Germany
| | - Max Schwenk
- Institute of Physical Chemistry, Hamburg University , Grindelallee 117, 20146 Hamburg , Germany
| | - Birgit Hankiewicz
- Institute of Physical Chemistry, Hamburg University , Grindelallee 117, 20146 Hamburg , Germany
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4
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Huang GR, Carrillo JM, Wang Y, Do C, Porcar L, Sumpter B, Chen WR. An exact inversion method for extracting orientation ordering by small-angle scattering. Phys Chem Chem Phys 2021; 23:4120-4132. [PMID: 33592085 DOI: 10.1039/d0cp05886f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We outline a nonparametric inversion strategy for determining the orientation distribution function (ODF) of sheared interacting rods using small-angle scattering techniques. With the presence of direct inter-rod interaction and fluid mechanical forces, the scattering spectra are no longer characterized by the azimuthal symmetry in the coordinates defined by the principal directions of simple shear conditions, which severely compounds the reconstruction of ODFs based on currently available methods developed for dilute systems. Using a real spherical harmonic expansion scheme, the real-space ODFs are uniquely determined from the anisotropic scattering spectra and their numerical accuracy is verified computationally. Our method can be generalized to extract ODFs of uniaxially anisotropic objects under different flow conditions in a properly transformed reference frame with suitable basis vectors.
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Affiliation(s)
- Guan-Rong Huang
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
| | - Jan Michael Carrillo
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
| | - Yangyang Wang
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
| | - Changwoo Do
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
| | - Lionel Porcar
- Institut Laue-Langevin, B. P. 156, F-38042 Grenoble Cedex 9, France
| | - Bobby Sumpter
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
| | - Wei-Ren Chen
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
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5
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Kreissl P, Holm C, Weeber R. Frequency-dependent magnetic susceptibility of magnetic nanoparticles in a polymer solution: a simulation study. SOFT MATTER 2021; 17:174-183. [PMID: 33165470 DOI: 10.1039/d0sm01554g] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Magnetic composite materials i.e. elastomers, polymer gels, or polymer solutions with embedded magnetic nanoparticles are useful for many technical and bio-medical applications. However, the microscopic details of the coupling mechanisms between the magnetic properties of the particles and the mechanical properties of the (visco)elastic polymer matrix remain unresolved. Here we study the response of a single-domain spherical magnetic nanoparticle that is suspended in a polymer solution to alternating magnetic fields. As interactions we consider only excluded volume interactions with the polymers and hydrodynamic interactions mediated through the solvent. The AC susceptibility spectra are calculated using a linear response Green-Kubo approach, and the influences of changing polymer concentration and polymer length are investigated. Our data is compared to recent measurements of the AC susceptibility for a typical magnetic composite system [Roeben et al., Colloid Polym. Sci., 2014, 2013-2023], and demonstrates the importance of hydrodynamic coupling in such systems.
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Affiliation(s)
- Patrick Kreissl
- Institute for Computational Physics, University of Stuttgart, Allmandring 3, 70569 Stuttgart, Germany.
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6
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Huang GR, Wang Y, Do C, Shinohara Y, Egami T, Porcar L, Liu Y, Chen WR. Orientational Distribution Function of Aligned Elongated Molecules and Particulates Determined from Their Scattering Signature. ACS Macro Lett 2019; 8:1257-1262. [PMID: 35651160 DOI: 10.1021/acsmacrolett.9b00496] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We present a strategy for quantitatively evaluating the field-induced alignment of nonspherical particles using small-angle scattering techniques. The orientational distribution function (ODF) is determined from the anisotropic scattering intensity via the scheme of real spherical harmonic expansion. Our developed approach is simple and analytical and does not require a presumptive hypothesis of the ODF as an input in data analysis. A model study of aligned rigid rods demonstrates the validity of this proposed approach to facilitate the quantitative structural characterization of materials with preferred orientational states.
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Affiliation(s)
- Guan-Rong Huang
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Yangyang Wang
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Changwoo Do
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Yuya Shinohara
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Takeshi Egami
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.,Department of Materials Science and Engineering and Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Lionel Porcar
- Institut Laue-Langevin, B.P. 156, F-38042 Cedex 9 Grenoble, France
| | - Yun Liu
- The NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6100, United States.,Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716, United States
| | - Wei-Ren Chen
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
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7
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Vasireddi R, Kruse J, Vakili M, Kulkarni S, Keller TF, Monteiro DCF, Trebbin M. Solution blow spinning of polymer/nanocomposite micro-/nanofibers with tunable diameters and morphologies using a gas dynamic virtual nozzle. Sci Rep 2019; 9:14297. [PMID: 31586141 PMCID: PMC6778068 DOI: 10.1038/s41598-019-50477-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Accepted: 09/12/2019] [Indexed: 12/31/2022] Open
Abstract
Uniform endless fibers are ubiquitous and their applications range from functional textiles over biomedical engineering to high-performance filtering and drug delivery systems. Here, we report a new method for the direct, reproducible fabrication of uniform polymer and composite micro-/nanofibers using a microfluidic gas flow focusing nozzle (Gas Dynamic Virtual Nozzle (GDVN)) relinquishing the need for external fiber pulling mechanisms. Compared to other methods, this technique is inexpensive, user-friendly and permits precise fiber diameter control (~250 nm to ~15 µm), high production rate (m/s-range) and direct fiber deposition without clogging due to stable, gas-focused jetting. Control over shape (flat or round) and surface patterning are achieved by simply tuning the air pressure and polymer concentration. The main thinning process happens after the polymer exits the device and is, therefore, mostly independent of the nozzle's internal geometry. Nevertheless, the lithography-based device design is versatile, allowing for precise flow-field control for operation stability as well as particle alignment control. As an example, we demonstrate the successful production of endless hematite nanocomposite fibers which highlights this technology's exciting possibilities that can lead to the fabrication of multifunctional/stimuli-responsive fibers with thermal and electrical conductivity, magnetic properties and enhanced mechanical stability.
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Affiliation(s)
- Ramakrishna Vasireddi
- The Hamburg Center for Ultrafast Imaging (CUI), University of Hamburg, Luruper Chaussee 149, 22761, Hamburg, Germany
| | - Joscha Kruse
- The Hamburg Center for Ultrafast Imaging (CUI), University of Hamburg, Luruper Chaussee 149, 22761, Hamburg, Germany
- Donostia International Physics Center (DIPC), Manuel Lardizabal Ibilbidea 4, 20018, San Sebastian, Spain
| | - Mohammad Vakili
- The Hamburg Center for Ultrafast Imaging (CUI), University of Hamburg, Luruper Chaussee 149, 22761, Hamburg, Germany
| | | | - Thomas F Keller
- Deutsches Elektronen-Synchrotron (DESY), 22607, Hamburg, Germany
- Department of Physics, University of Hamburg, 20355, Hamburg, Germany
| | - Diana C F Monteiro
- The Hamburg Center for Ultrafast Imaging (CUI), University of Hamburg, Luruper Chaussee 149, 22761, Hamburg, Germany
| | - Martin Trebbin
- Department of Chemistry, The State University of New York, University at Buffalo, 760 Natural Sciences Complex, Buffalo, New York, 14260-3000, USA.
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8
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Bender P, Zákutná D, Disch S, Marcano L, Alba Venero D, Honecker D. Using the singular value decomposition to extract 2D correlation functions from scattering patterns. ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES 2019; 75:766-771. [PMID: 31475920 DOI: 10.1107/s205327331900891x] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2019] [Accepted: 06/21/2019] [Indexed: 11/10/2022]
Abstract
The truncated singular value decomposition (TSVD) is applied to extract the underlying 2D correlation functions from small-angle scattering patterns. The approach is tested by transforming the simulated data of ellipsoidal particles and it is shown that also in the case of anisotropic patterns (i.e. aligned ellipsoids) the derived correlation functions correspond to the theoretically predicted profiles. Furthermore, the TSVD is used to analyze the small-angle X-ray scattering patterns of colloidal dispersions of hematite spindles and magnetotactic bacteria in the presence of magnetic fields, to verify that this approach can be applied to extract model-free the scattering profiles of anisotropic scatterers from noisy data.
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Affiliation(s)
- Philipp Bender
- Physics and Materials Science Research Unit, University of Luxembourg, 162A Avenue de la Faïencerie, L-1511 Luxembourg, Grand Duchy of Luxembourg
| | - Dominika Zákutná
- Large Scale Structures Group, Institut Laue-Langevin, 71 Avenue des Martyrs, F-38042 Grenoble, France
| | - Sabrina Disch
- Department für Chemie, Universität zu Köln, Luxemburger Strasse 116, D-50939 Köln, Germany
| | - Lourdes Marcano
- Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, D-12489 Berlin, Germany
| | - Diego Alba Venero
- ISIS Neutron and Muon Facility, Rutherford Appleton Laboratory, Chilton, OX11 0QX, UK
| | - Dirk Honecker
- Large Scale Structures Group, Institut Laue-Langevin, 71 Avenue des Martyrs, F-38042 Grenoble, France
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9
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Zákutná D, Falke Y, Dresen D, Prévost S, Bender P, Honecker D, Disch S. Morphological and crystallographic orientation of hematite spindles in an applied magnetic field. NANOSCALE 2019; 11:7149-7156. [PMID: 30778464 DOI: 10.1039/c8nr09583c] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The magnetic response of spindle-shaped hematite (α-Fe2O3) nanoparticles was investigated by simultaneous small-angle and wide-angle X-ray scattering (SAXS/WAXS) experiments. The field-dependent magnetic and nematic order parameters of the magnetic single-domain nanospindles in a static magnetic field are fully described by SAXS simulations of an oriented ellipsoid with the implemented Langevin function. The experimental scattering intensities of the spindle-like particles can be modeled simply by using the geometrical (length, radius, size distribution) and magnetic parameters (strength of magnetic field, magnetic moment) obtained from isotropic SAXS and macroscopic magnetization measurements, respectively. Whereas SAXS gives information on the morphological particle orientation in the applied field, WAXS texture analysis elucidates the atomic scale orientation of the magnetic easy direction in the hematite crystal structure. Our results strongly suggest the tendency for uniaxial anisotropy but indicate significant thermal fluctuations of the particle moments within the hematite basal plane.
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Affiliation(s)
- Dominika Zákutná
- Large Scale Structures group, Institut Laue-Langevin, 71 avenue des Martyrs, F-38042 Grenoble, France
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10
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Magnetic Freedericksz transition in a ferronematic liquid crystal doped with spindle magnetic particles. J Mol Liq 2018. [DOI: 10.1016/j.molliq.2017.10.106] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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11
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Nack A, Seifert J, Passow C, Wagner J. Hindered nematic alignment of hematite spindles in poly(N-isopropylacrylamide) hydrogels: a small-angle X-ray scattering and rheology study. J Appl Crystallogr 2018. [DOI: 10.1107/s1600576717017411] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Field-induced changes to the mesostructure of ferrogels consisting of spindle-shaped hematite particles and poly(N-isopropylacrylamide) are investigated by means of small-angle X-ray scattering (SAXS). Related field-induced changes to the macroscopic viscoelastic properties of these composites are probed by means of oscillatory shear experiments in an external magnetic field. Because of their magnetic moment and magnetic anisotropy, the hematite spindles align with their long axis perpendicular to the direction of an external magnetic field. The field-induced torque acting on the magnetic particles leads to an elastic deformation of the hydrogel matrix. Thus, the field-dependent orientational distribution functions of anisotropic particles acting as microrheological probes depend on the elastic modulus of the hydrogel matrix. The orientational distribution functions are determined by means of SAXS experiments as a function of the varying flux density of an external magnetic field. With increasing elasticity of the hydrogels, tunedviathe polymer volume fraction and the crosslinking density, the field-induced alignment of these anisotropic magnetic particles is progressively hindered. The microrheological results are in accordance with macrorheological experiments indicating increasing elasticity with increasing flux density of an external field.
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12
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Herold E, Hellmann R, Wagner J. Virial coefficients of anisotropic hard solids of revolution: The detailed influence of the particle geometry. J Chem Phys 2017; 147:204102. [DOI: 10.1063/1.5004687] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Elisabeth Herold
- Institut für Chemie, Universität Rostock, D-18051 Rostock,
Germany
| | - Robert Hellmann
- Institut für Chemie, Universität Rostock, D-18051 Rostock,
Germany
| | - Joachim Wagner
- Institut für Chemie, Universität Rostock, D-18051 Rostock,
Germany
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13
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Passow C, ten Hagen B, Löwen H, Wagner J. Depolarized light scattering from prolate anisotropic particles: The influence of the particle shape on the field autocorrelation function. J Chem Phys 2015; 143:044903. [DOI: 10.1063/1.4926931] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Affiliation(s)
| | - Borge ten Hagen
- Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany
| | - Hartmut Löwen
- Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany
| | - Joachim Wagner
- Institut für Chemie, Universität Rostock, D-18051 Rostock, Germany
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14
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Hoffelner D, Kundt M, Schmidt AM, Kentzinger E, Bender P, Disch S. Directing the orientational alignment of anisotropic magnetic nanoparticles using dynamic magnetic fields. Faraday Discuss 2015; 181:449-61. [DOI: 10.1039/c4fd00242c] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The structure-directing influence of static and dynamic, i.e. rotating, magnetic fields on the orientational alignment of spindle-type hematite particles with a high aspect ratio is investigated. Structural characterization using electron microscopy and small-angle X-ray scattering confirms a nearly collinear particle arrangement with orientation of the main particle axis either parallel or perpendicular to the substrate as directed by the magnetic field geometry. The combination of large structural and magnetocrystalline anisotropies results in significantly different, strongly anisotropic magnetic properties of the assemblies revealed by directional magnetization measurements.
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Affiliation(s)
- Daniel Hoffelner
- Department Chemie
- Institut für Physikalische Chemie
- Universität zu Köln
- D-50939 Köln
- Germany
| | - Matthias Kundt
- Department Chemie
- Institut für Physikalische Chemie
- Universität zu Köln
- D-50939 Köln
- Germany
| | - Annette M. Schmidt
- Department Chemie
- Institut für Physikalische Chemie
- Universität zu Köln
- D-50939 Köln
- Germany
| | - Emmanuel Kentzinger
- Jülich Centre for Neutron Science JCNS
- Peter Grünberg Institut PGI
- JARA-FIT
- D-52425 Jülich
- Germany
| | - Philipp Bender
- Experimentalphysik
- Universität des Saarlandes
- D-66041 Saarbrücken
- Germany
| | - Sabrina Disch
- Department Chemie
- Institut für Physikalische Chemie
- Universität zu Köln
- D-50939 Köln
- Germany
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15
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Bakuzis AF, Branquinho LC, Luiz e Castro L, de Amaral e Eloi MT, Miotto R. Chain formation and aging process in biocompatible polydisperse ferrofluids: experimental investigation and Monte Carlo simulations. Adv Colloid Interface Sci 2013; 191-192:1-21. [PMID: 23360743 DOI: 10.1016/j.cis.2012.12.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2012] [Revised: 12/27/2012] [Accepted: 12/28/2012] [Indexed: 11/25/2022]
Abstract
We review the use of Monte Carlo simulations in the description of magnetic nanoparticles dispersed in a liquid carrier. Our main focus is the use of theory and simulation as tools for the description of the properties of ferrofluids. In particular, we report on the influence of polydispersity and short-range interaction on the self-organization of nanoparticles. Such contributions are shown to be extremely important for systems characterized by particles with diameters smaller than 10nm. A new 3D polydisperse Monte Carlo implementation for biocompatible magnetic colloids is proposed. As an example, theoretical and simulation results for an ionic-surfacted ferrofluid dispersed in a NaCl solution are directly compared to experimental data (transmission electron microscopy - TEM, magneto-transmissivity, and electron magnetic resonance - EMR). Our combined theoretical and experimental results suggest that during the aging process two possible mechanisms are likely to be observed: the nanoparticle's grafting decreases due to aggregate formation and the Hamaker constant increases due to oxidation. In addition, we also briefly discuss theoretical agglomerate formation models and compare them to experimental data.
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16
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Wagner J, Märkert C, Fischer B, Müller L. Direction dependent diffusion of aligned magnetic rods by means of x-ray photon correlation spectroscopy. PHYSICAL REVIEW LETTERS 2013; 110:048301. [PMID: 25166207 DOI: 10.1103/physrevlett.110.048301] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Indexed: 06/03/2023]
Abstract
Rodlike hematite particles in suspension align perpendicular to an external magnetic field due to a negative anisotropy of their magnetic susceptibility Δχ. The diffusion tensor consists of two principal constants D(∥) and D(⊥) for the diffusion parallel and perpendicular to the long particle axis. X-ray photon correlation spectroscopy is capable of probing the diffusive motion in optically opaque suspensions of rodlike hematite particles parallel to the direction of the scattering vector Q. Choosing Q parallel or perpendicular to the direction of an external magnetic field H the direction dependent intermediate scattering function is measured by means of x-ray photon correlation spectroscopy. From the intermediate scattering function in both directions the principal diffusion constants D(∥) and D(⊥) are determined. The ratio D(∥)/D(⊥) increases with increasing aspect ratio of the particles and can be described via a rescaled theoretical approach for prolate ellipsoids of revolution.
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Affiliation(s)
- Joachim Wagner
- Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany
| | - Christian Märkert
- Physikalische Chemie, Universität des Saarlandes, Campus B22, 66123 Saarbrücken, Germany
| | - Birgit Fischer
- Deutsches Elektronensynchrotron, Notkestraße 85, 22607 Hamburg, Germany
| | - Leonard Müller
- Deutsches Elektronensynchrotron, Notkestraße 85, 22607 Hamburg, Germany
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