Chain formation in a magnetic fluid under the influence of strong external magnetic fields studied by small angle neutron scattering
TL;DR: In this article, the authors studied the aggregation of magnetic particles into chain-like structures in a cobalt-based magnetic fluid, exposed to external magnetic fields and observed a maximum correlation length of ∼65 nm equivalent to 3-4 particles up to highest magnetic fields.
Abstract: We studied the aggregation of magnetic particles into chain-like structures in a cobalt-based magnetic fluid, exposed to external magnetic fields. The length of chain segments in very strong magnetic fields of up to 2 Tesla was measured in situ using small angle neutron scattering. Arrangement of the magnetic particles was studied with the scattering vector aligned parallel to the magnetic field lines, and at angles of 30° and 60° with respect to . Although chains several hundred particles in length were predicted, we observe a maximum correlation length of ∼65 nm equivalent to 3–4 particles up to highest fields. We speculate that the interaction between chains, i.e., the interplay between the entropy and energy of the system combined with the particular properties of the magnetic dipole–dipole interaction ultimately decide the length of the particle chains.
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TL;DR: In this article, the authors presented the results of a project for the U.S. Department of Energy, Office of Basic Energy Sciences, under Award No. DE-SC0005051 and DE-FG02-06ER46275.
Abstract: Deutsche Forschungsgemeinschaft (Project No. BE 2464/10-3), the EU-FP7 project “NANOPYME” (310516), and the EU Horizon-2020 project “AMPHIBIAN” (720853). M. R. E. was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Award No. DE-SC0005051. F. B. thanks Andreas Ulbricht for fruitful discussions over the many years. C. L. was funded by the U.S. Department of
Energy through the University of Minnesota Center for Quantum Materials under DE-FG02-06ER46275 and DESC-0016371. S. D. acknowledges financial support from the
German Research Foundation (DFG Emmy Noether Grant No. DI 1788/2-1).
164 citations
Cites background from "Chain formation in a magnetic fluid..."
...Formation of chainlike structures that orient in the direction of an applied magnetic field was observed for magnetosomes (Hoell et al., 2004) as well as for cobalt nanoparticles (Barrett et al., 2011)....
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TL;DR: In this article, the authors revisit the advances in the basic physical concepts and predictive analytical and simulation tools, focusing on recent developments in the understanding and prediction of phenomena induced by magnetic fields both in uniform fields (for example, chain formation) and in magnetic gradients (cooperative magnetophoresis).
Abstract: In recent years, there has been a great progress in the development of superparamagnetic particles targeted to a wide range of applications, including fields as diverse as biotechnology or waste removal. However, the physics behind their behaviour under usual conditions (diluted dispersions and high magnetic fields) has many, fundamental, open questions. In this review, we revisit the advances in the basic physical concepts and predictive analytical and simulation tools. We focus on recent developments in the understanding and prediction of phenomena induced by magnetic fields both in uniform fields (for example, chain formation) and in magnetic gradients (cooperative magnetophoresis).
140 citations
TL;DR: In this article, the authors describe the recent advances in the development of predictive theoretical tools for the study of directed self-assembly of superparamagnetic colloids under magnetic fields, and present a practical view of how to employ the new concepts (derived from thermodynamic theory) to predict the possible assembled structures from the properties of the colloids and thermodynamic conditions.
Abstract: Self-assembly processes are very important in material sciences but are particularly difficult to predict quantitatively. This is the case for particulate magnetic materials in which field-induced self-assembly processes are essential. This article describes the recent advances in the development of predictive theoretical tools for the study of directed self-assembly of superparamagnetic colloids under magnetic fields. A practical view is presented of how to employ the new concepts (derived from thermodynamic theory) to predict the possible assembled structures from the properties of the colloids and thermodynamic conditions. Quantitative prediction of kinetics is also discussed for the cases in which equilibrium theory is not relevant. Finally, an outline of fundamental aspects of the theory is presented.
95 citations
TL;DR: A comprehensive review on the different aspects of Ferrofluids research is presented in this paper, where the synthesis and stabilization of various types of FFs are discussed followed by their physicochemical features such as polydispersity, magnetic behavior, dipolar interactions, formation of chainlike aggregates, and long-range ordering.
Abstract: Ferrofluids (FFs) or magnetic nanofluids are incredible smart materials consisting of ultrafine magnetic nanoparticles suspended in a liquid carrier medium, which exhibit both fluidity and magnetic controllability. Studies involving the dynamics and physicochemical properties of these magnetic nanofluids are an interdisciplinary area of research attracting researchers from different fields of science and technology. Herein, a comprehensive Review on the different aspects of FF research is presented. First, the synthesis and stabilization of various types of FFs are discussed followed by their physicochemical features such as polydispersity, magnetic behavior, dipolar interactions, formation of chainlike aggregates, and long-range ordering. The Review also details the rheological and thermal properties, dynamic instabilities, phase behavior, and particle assemblies in FFs to form complex multipolar geometries, photonic nanostructures, labyrinth structures, thin films, and droplets. Many important characterization techniques for probing FF properties are also briefly discussed, and the numerous innovative applications and future prospects of FFs are outlined.
81 citations
TL;DR: A phenomenal thixotropic model was employed to analyze the experimental results, indicating that a more specific model for ferrofluids is needed and contribute to a better understanding of the microscopic mechanism of the complex rheological behaviors of ferro fluids.
Abstract: The thixotropic behaviors of ferrofluid samples of different particle concentration were studied using different measurement methods, including the three interval thixotropic test and the hysteresis loop test. The experimental results demonstrated that ferrofluids exhibit significant thixotropic behaviors and the microstructural evolution in ferrofluids behind the macroscopic rheological mechanics is discussed. The influence of magnetic field strength, particle concentration and temperature on the thixotropy of ferrofluids was also analyzed. Microscopic ferrofluid theory was adopted to study the thixotropic behaviors of ferrofluids under different shearing conditions, indicating that different thixotropic behaviors of ferrofluids can be induced by the presence and evolution of different kinds of microstructures, such as linear chain-like and dense drop-like structures. Furthermore, a phenomenal thixotropic model was employed to analyze the experimental results, indicating that a more specific model for ferrofluids is needed. These findings contribute to a better understanding of the microscopic mechanism of the complex rheological behaviors of ferrofluids.
24 citations
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TL;DR: In this article, the formation of structures of magnetic nanoparticles has been shown to have significant influence on the magnetoviscous behavior of ferrofluids and the dependence of this structure formation on the magnetic field strength and shear stress applied to the fluid leads to strong changes of viscosity and to the appearance of viscoelastic effects in the fluids.
Abstract: Investigations of the properties, the flow and the application possibilities of suspensions of magnetic nanoparticles are an extremely lively research field nowadays. In particular, the biomedical application and the investigation of the rheological properties of these so-called ferrofluids gained high importance during the last years. Within this paper particular focus will be put on recent development in the field of rheological investigations of ferrofluids and their importance for the general treatment of ferrofluids. As will be outlined, recent experimental as well as theoretical investigations have shown that the formation of structures of magnetic nanoparticles has significant influence on the magnetoviscous behaviour of ferrofluids. The dependence of this structure formation on the magnetic field strength and shear stress applied to the fluid leads to strong changes of viscosity and to the appearance of viscoelastic effects in the fluids. The new findings have led to consistent microscopic models for the viscous properties of ferrofluids and they have driven the development of a macroscopic theory predicting new effects in ferrofluid dynamics.
272 citations
01 Jan 2009
TL;DR: In this article, the surface instability of Ferrofluid surfaces is investigated in the context of magnetic nanoparticles and their applications in biomedical applications. But the authors focus on the application of magnetic nanoparticles in medical applications.
Abstract: Synthesis and Characterization.- Thermodynamics, Electrodynamics, and Ferrofluid Dynamics.- Surface Instabilities of Ferrofluids.- Ferrofluid Structure and Rheology.- Biomedical Applications of Magnetic Nanoparticles.- Technical Applications.
233 citations
01 Aug 1970
TL;DR: In this article, the authors discuss the properties of the equation of state and the static correlations for spherical ferromagnetic grains, at thermal equilibrium, in a passive fluid, at high external fields, low concentrations, and not too high temperatures, the grains tend to formchains along the directions ofH.
Abstract: We discuss some properties of the equation of state and of the static correlations for spherical ferromagnetic grains, at thermal equilibrium, in a passive fluid. At high external fieldsH, low concentrations, and not too high temperatures, the grains tend to formchains along the directions ofH. In zero field (but otherwise identical conditions), some chains are still present but oriented at random and in competition with closed rings and clusters. Various experimental methods which could give information on these chain structures are listed.
228 citations
TL;DR: The formation of clusters is found to enhance the magnetization at weak fields and thus leads to a larger initial susceptibility, and the observed susceptibility is considerably lowered when compared to ferrofluids.
Abstract: We investigate in detail the initial susceptibility, magnetization curves, and microstructure of ferrofluids in various concentration and particle dipole moment ranges by means of molecular dynamics simulations. We use the Ewald summation for the long-range dipolar interactions, take explicitly into account the translational and rotational degrees of freedom, coupled to a Langevin thermostat. When the dipolar interaction energy is comparable with the thermal energy, the simulation results on the magnetization properties agree with the theoretical predictions very well. For stronger dipolar couplings, however, we find systematic deviations from the theoretical curves. We analyze in detail the observed microstructure of the fluids under different conditions. The formation of clusters is found to enhance the magnetization at weak fields and thus leads to a larger initial susceptibility. The influence of the particle aggregation is isolated by studying ferro-solids, which consist of magnetic dipoles frozen in at random locations but which are free to rotate. Due to the artificial suppression of clusters in ferrosolids the observed susceptibility is considerably lowered when compared to ferrofluids.
198 citations