Generating strange magnetic and dielectric interactions: Classical molecules and particle foams

Martin, James E.; Anderson, Robert A.; Williamson, Rodney L.

doi:10.1063/1.1528892

Cited by 92 publications

(60 citation statements)

References 14 publications

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“…Paramagnetic colloidal suspensions have been utilized for a number of innovative applications in a variety of fields such as smart fluids [e.g., magnetorheological (MR) fluids] [1][2][3], biomedical imaging and sensing [4], unique directed assembly structures [5][6][7], self-propelled swimming structures [8,9], force probing [10,11], and models for statistical mechanics [12,13]. In many of these applications, the force between these paramagnetic particles needs to be accurately calculated.…”

Section: Introductionmentioning

confidence: 99%

Numerical calculation of interaction forces between paramagnetic colloids in two-dimensional systems

Toffoletto

Biswal

2014

Phys. Rev. E

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Typically the force between paramagnetic particles in a uniform magnetic field is described using the dipolar model, which is inaccurate when particles are in close proximity to each other. Instead, the exact force between paramagnetic particles can be determined by solving a three-dimensional Laplace's equation for magnetostatics under specified boundary conditions and calculating the Maxwell stress tensor. The analytical solution to this multi-boundary-condition Laplace's equation can be obtained by using a solid harmonics expansion in conjunction with the Hobson formula. However, for a multibody system, finite truncation of the Hobson formula does not lead to convergence of the expansion at all points, which makes the approximation physically unrealistic. Here we present a numerical method for solving this Laplace's equation for magnetostatics. This method uses a smoothed representation to replace all the boundary conditions. A two-step propagation is used to dramatically accelerate the calculation without losing accuracy. Using this method, we calculate the force between two paramagnetic particles in a uniform and a rotational external field and compare our results with other models. Furthermore, the many-body effects for three-particle, ten-particle, and 24-particle systems are examined using the same method. We also calculate the interaction between particles with different magnetic susceptibilities and particle diameters. The Laplace's equation solver method described in this article that is used to determine the force between paramagnetic particles is shown to be very useful for dynamic simulations for both two-particle systems and a large cluster of particles.

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Section: Introductionmentioning

confidence: 99%

Numerical calculation of interaction forces between paramagnetic colloids in two-dimensional systems

Toffoletto

Biswal

2014

Phys. Rev. E

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“…Finally, a triaxial magnetic field can be created by combining three orthogonal magnetic fields, at least two of which are ac. Composites formed in triaxial fields can have a variety of structures [10,12], but the important point is that triaxial fields can be used to highly optimize the properties of particle composites and this deserves further discussion.…”

Section: Methodsmentioning

confidence: 99%

“…Particle interactions in triaxial fields are complicated, and are treated in detail in [10], but a qualitative discussion here should serve as a practical guide as to their effects. The magnetic interactions between particles are largely due to their dipole moments.…”

Section: Methodsmentioning

confidence: 99%

“…A detailed description of these simulations can be found in reference. [10] From these simulated structures we have obtained the structural parameters for composites formed in uniaxial and biaxial fields, as well as for random composites. In the reduced stress units, ′ σ meas = σ meas / 1 2 µ eff µ 0 H 0 2 , where the stress is normalized by the energy density of the field, we have predicted that the reduced stress of a random 10 vol.% composite should be -2.7, the minus sign denoting a compressive stress.…”

Section: Magnetostrictionmentioning

confidence: 99%

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Magnetostriction of field-structured magnetoelastomers.

Gulley

Read²,

Martin³

et al. 2005

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Field-structured magnetic particle composites are an important new class of materials that have great potential as both sensors and actuators. These materials are synthesized by suspending magnetic particles in a polymeric resin and subjecting these to magnetic fields while the resin polymerizes. If a simple uniaxial magnetic field is used, the particles will form chains, yielding composites whose magnetic susceptibility is enhanced along a single direction. A biaxial magnetic field, comprised of two orthogonal ac fields, forms particle sheets, yielding composites whose magnetic susceptibility is enhanced along two principal directions. A balanced triaxial magnetic field can be used to enhance the susceptibility in all directions, and biased heterodyned triaxial magnetic fields are especially effective for producing composites with a greatly enhanced susceptibility along a single axis. Magnetostriction is quadratic in the susceptibility, so increasing the composite susceptibility is important to developing actuators that function well at modest fields. To investigate magnetostriction in these field-structured composites we have constructed a sensitive, constant-stress apparatus capable of 1 ppm strain resolution. The sample geometry is designed to minimize demagnetizing field effects. With this apparatus we have demonstrated field-structured composites with nearly 10,000 ppm strain. 3 Executive SummaryThe purpose of this project was to determine whether elastomeric composite materials can be synthesized in such a way as to have significant levels of magnetostriction, much greater than that possible with piezoelectric materials. In fact, it is possible, especially if the composites are synthesized in the presence of magnetic fields. At best, we have produced materials that exhibit roughly 100 times the strain of piezo materials.Magnetostriction -roughly speaking the deformation of a material subjected to a uniform magnetic field -is a property one normally associates with solid magnetic materials, not elastomeric composites. When a field is applied to such a material it contracts along the field so as to increase the interactions between the magnetic spins. If one has such a magnetostrictive material in particulate form, then it is possible to make a soft composite material that will in some measure exhibit magnetostriction due to the magnetostriction of the constituent particles. This is not our approach, but such composites have been reported and have been found to have modest magnetostriction.The composites we synthesize and study are made with Fe and Ni particles, materials which themselves exhibit negligible magnetostrictive strain. In the presence of a magnetic field these particles do acquire a magnetic moment, however, and it is the dipolar interactions between these magnetic moments that gives rise to magnetostriction of the composite itself. The interactions between dipoles is strongly dependent on the organization of the particles within the composite. We can create a variety of distinct compos...

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“…Our mixing system uses a triaxial magnetic field described in Martin et al [1]. This technique uses three nested Helmholtz coils [ Fig.…”

Section: Sample Mixingmentioning

confidence: 99%

Magnetophoretic bead trapping in a high-flowrate biological detection system.

Galambos¹,

Hopkins²,

Rahimian³

et al. 2005

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This report contains the summary of the "Magnetophoretic Bead Trapping in a High-Flowrate Biological Detection System" LDRD project 74795. The objective of this project is to develop a novel biodetection system for highthroughput sample analysis. The chief application of this system is in detection of very low concentrations of target molecules from a complex liquid solution containing many different constituents -some of which may interfere with identification of the target molecule. The system is also designed to handle air sampling by using an aerosol system (for instance a WESP -Wet Electro-Static Precipitator, or an impact spray system) to get air sample constituents into the liquid volume. The system described herein automatically takes the raw liquid sample, whether air converted or initially liquid matrix, and mixes in magnetic detector beads that capture the targets of interest and then performs the sample cleanup function, allowing increased sensitivity and eliminating most false positives and false negatives at a downstream detector.The surfaces of the beads can be functionalized in a variety of ways in order to maximize the number of targets to be captured and concentrated. Bacteria and viruses are captured using antibodies to surface proteins on bacterial cell walls or viral particle coats. In combination with a cell lysis or PCR (Polymerase Chain Reaction), the beads can be used as a DNA or RNA probe to capture nucleic acid patterns of interest. The sample cleanup capability of this system would allow different raw biological samples, such as blood or saliva to be analyzed for the presence of different infectious agents (e.g. smallpox or SARS). For future studies, we envision functionalizing bead surfaces to bind to chemical weapons agents, radio-isotopes, and explosives.The two main objectives of this project were to explore methods for enhancing the mixing of the capture microspheres in the sample, and to develop a novel high-throughput magnetic microsphere trap. We have developed a novel technique using the magnetic capture microspheres as "stirrer bars" in a fluid sample to enhance target binding to the microsphere surfaces. We have also made progress in developing a polymer-MEMS electromagnet for trapping magnetic spheres in a high-flowrate fluid format.4

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Generating strange magnetic and dielectric interactions: Classical molecules and particle foams

Cited by 92 publications

References 14 publications

Numerical calculation of interaction forces between paramagnetic colloids in two-dimensional systems

Numerical calculation of interaction forces between paramagnetic colloids in two-dimensional systems

Magnetostriction of field-structured magnetoelastomers.

Magnetophoretic bead trapping in a high-flowrate biological detection system.

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