Colloidal Magnetic Fluids

Research into the fascinating properties and applications of magnetic fluids - also called ferrofluids - is rapidly growing, making it necessary to provide, at regular intervals, a coherent and tutorial account of the combined theoretical and experimental advances in the field. This volume is an outgrow of seven years of research by some 30 interdisciplinary groups of scientists: theoretical physicists describing the behaviour of such complex fluids, chemical engineers synthesizing nanosize magnetic particles, experimentalist measuring the fluid properties and mechanical engineers exploring the many applications such fluids offer, in turn providing application-guided feedback to the modellers and requests for the preparation of new fluid types to chemists, in particular those providing optimum response to given magnetic field configurations. Moreover, recent developments towards biomedical applications widens this spectrum to include medicine and pharmacology. Consisting of six large chapters on synthesis and characterization, thermo- and electrodynamics, surface instabilities, structure and rheology, biomedical applications as well as engineering and technical applications, this work is both a unique source of reference for anyone working in the field and a suitable introduction for newcomers to the field.

Research into the fascinating properties and applications of magnetic fluids - also called ferrofluids - is rapidly growing, making it necessary to provide, at regular intervals, a coherent and tutorial account of the combined theoretical and experimental advances in the field. This volume is an outgrow of seven years of research by some 30 interdisciplinary groups of scientists: theoretical physicists describing the behaviour of such complex fluids, chemical engineers synthesizing nanosize magnetic particles, experimentalist measuring the fluid properties and mechanical engineers exploring the many applications such fluids offer, in turn providing application-guided feedback to the modellers and requests for the preparation of new fluid types to chemists, in particular those providing optimum response to given magnetic field configurations. Moreover, recent developments towards biomedical applications widens this spectrum to include medicine and pharmacology. Consisting of six large chapters on synthesis and characterization, thermo- and electrodynamics, surface instabilities, structure and rheology, biomedical applications as well as engineering and technical applications, this work is both a unique source of reference for anyone working in the field and a suitable introduction for newcomers to the field.

The feasibility of using high gradient magnetic separation (HGMS) to separate the Fe304 nanoparticles was studied in this work. We present a general model for nanoparticle capture based on calculating the limit of static nanoparticle buildup around the collection wires in an HGMS column. Model predictions were compared successfully with experimental results from a bench-scale HGMS column. Permanent capture of individual nanoparticles is limited by diffusion away from the wires; however, 60-125 nm aggregates of particles can be captured permanently in the bench-scale column. The model provided estimates of the minimum particle size for permanent capture of individual nanoparticles and nanoparticle aggregates.

Magnetic control of the properties and the flow of liquids is a challenging field for basic research and for applications. This book is meant to be both an introduction to, and a state-of-the-art review of, this topic. Written in the form of a set of lectures and tutorial reviews, the book addresses the synthesis and characterization of magnetic fluids, their hydrodynamical description and their rheological properties. The book closes with an account of magnetic drug targeting.

In this chapter, we review the experimental and theoretical modeling of structural and dynamical properties of colloidal magnetic fluids at equilibrium. Presently, several prototype experimental systems are very well characterized. We survey the different models, which help to reach a comprehensive knowledge of these complex magnetic fluids. One prime example is the ongoing investigation of the realistic interparticle potentials that drive the formation of the different phase states observed experimentally. Further, a stochastic equation approach for the description of tracer diffusion, viscoelasticity, and dielectric relaxation at equilibrium in colloidal ferrofluids is discussed.

"Our main goal is to study certain aspects of the dynamics of fluids with magnetic particles in suspension, based on their promising practical applications as new materials as welI as on its fundamental scientific interest.In the introduction we brief the reader on the most essential properties of the system. We have characterized the monodomain magnetic particles and the time scales inherent to magnetic fluids. Having introduced the rotational diffusion equation as the most convenient tool to take into account the different mechanism inftuencing the dynamics of the particles, we have also proposed a fruitful approach for solving it in any general situation. We have also highlighted the macroscopic properties of the magnetic fluid treated now as a continuous medium and showed up the different phenomena associated with the lack of stability in the system.In Chapter I we concentrate on two limit cases whose analysis is easier but very illustrative. The first part of the chapter is devoted to the study of a suspension of rigid dipoles, in which the magnetic moments are rigidly attached to the body of the particles themselves. In these conditions, if we apply an external magnetic field both the magnetic moment and the particle move together so that the magnetic torque acting upon it becomes zero. Thermal fluctuations tends to disrupt this order, and it turns out that, for instance, that the effective viscosity of the suspension depends on the dimensionless parameter comparing magnetic and thermal energies. In the second part we consider magnetic materials with finite anisotropy energy at high magnetic fields. For such monodomain particles the magnetic moments rapidly orient along the direction of the external field, and then as a second step the mechanical rotation of the particles takes place. In this case, the effective viscosity of the suspension is a function of the magnetic anisotropy constant of the material, of the volume of the particles as well as the thermal energy. Our results are compared to experimental measurements.The second chapter is concerned with the determination of the viscosity and of some magnetic and optical properties of magnetic fluids in the whole range of possible experimental situations. The magnetic moments and the particles inside the liquid reorient separately but their dynamics are coupled thus giving rise to a more intricate relaxation process. We have compared part of our results with available experimental data for different ferrofluids showing quite a good agreement.In Chapter III we joint to our discussion of magnetic fluids the presence of nonmagnetic particles of micrometer size and study their motion through the ferrofluid. The ferrofluid is considered now as a continuous medium with new transport coefficients already determined in the previous sections. Under the action of a rotating external magnetic field, we study the rotational motion of the nonmagnetic particles and compare our expressions to sorne measurements carried out in these composite systems. In this chapter we are also con cerned with the characterization of the hydrodynamic interactions among these particles in a carrier ferrofluid.Chapter IV is intended as a brief introduction to the multiple problems which arise when one handle the aggregation phenomena which may take place in these systerns. We study the kinetics of the forrnation of the aggregates by rneans of the Smoluchowski theory of coagulation in colloids. But we account for hydrodynarnic interactions which are not usually considered when studying such process and that gives rise to sorne corrections for high concentrations of particles. In addition, the rheology of the chains that are usually observed in systerns with dipolar interactions is given for a rather simplified situation in order to elucidate the effects of the dipolar magnetic interactions.Finally, we sum up our main conclusions and indicate some of the perspectives stimulated by the contents of this monograph and in which we plan to pursue work in the near future." -- TDX.

The understanding of how small solid particles operate at liquid interfaces is minimal. This book brings together the topics actively being investigated, with contributions from experts in the field. It will be of interest to researchers in chemistry, physics, chemical engineering, pharmacy, food science and materials science.