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Abstract In this study, we discuss the characterization and quantification of composite microstructures formed by the external field manipulation of high aspect ratio magnetic particles in an elastomeric matrix. In our prior work, we have demonstrated that the simultaneous application of electric and magnetic fields on hard magnetic particles with geometric anisotropy can create a hierarchy of structures at different length scales, which can be used to achieve a wide range of properties. We aim to characterize these hierarchical structures and relate them to final composite properties so we can achieve our ultimate goal of designing a material for a prescribed performance. The complex particle structures are formed during processing by using electric and magnetic fields, and they are then locked-in by curing the polymer matrix around the particles. The model materials used in the study are barium hexaferrite (BHF) particles and polydimethylsiloxane (PDMS) elastomer. BHF was selected for its hard magnetic properties and high geometric anisotropy. PDMS was selected for its good mechanical properties and its tunable curing kinetics. The resulting BHF-PDMS composites are magnetoactive, i.e., they will deform and actuate in response to magnetic fields. In order to investigate the resulting particle orientation, distribution and alignment and to predict the composite’s macro scale properties, we developed techniques to quantify the particle structures. The general framework we developed allows us to quantify and directly compare the microstructures created within the composites. To identify structures at the different length scales, images of the composite are taken using both optical microscopy and scanning electron microscopy. We then use ImageJ to analyze them and gather data on particle size, location, and orientation angle. The data is then exported to MATLAB, and is used to run a Minimum Spanning Tree Algorithm to classify the particle structures, and von Mises Distributions to quantify the alignment of said structures. Important findings show 1) the ability to control structure using a combination of external electric, magnetic and thermal fields; 2) that electric fields promote long range order while magnetic fields promote short-range order; and 3) the resulting hierarchical structure greatly influence bulk material properties. Manipulating particles in a composite material is technologically important because changes in microstructure can alter the properties of the bulk material. The multifield processing we investigate here can form the basis for next generation additive manufacturing platforms where desired properties are tailored locally through in-situ hierarchical control of particle arrangements.
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This content will become publicly available on March 1, 2026
Magnetic field-induced thermal behavior and sedimentation of strontium ferrite-PDMS composites for actuator applications
Magnetic composite polymers combine the properties of both magnet and polymers which enable them to produce complex shape magnetic components. These materials have potential applications ranging microfluidics, vibration dampers, actuators, and minimally invasive medical devices, because when magnetic fields are applied to them, they can change shape precisely, quickly, and consistently. Our study investigates the behavior of strontium ferrite particles [SrO(Fe2O3)6] suspended in polydimethylsiloxane (PDMS) under the influence of gravity, applied magnetic fields, and time dependent behavior at different temperatures. We found that curing the PDMS and strontium ferrite suspension without a magnetic field result in a well-distributed particle arrangement with no coagulation. However, the particles align along the magnetic field lines while curing in the presence of a magnetic field (Hallback Cylinder), leaving a clear PDMS layer on top, while there is very little sedimentation due to gravity. To check this, we fabricated a 40 mm long sample and conducted hysteresis measurements in vibrating sample magnetometer (VSM) at various positions, showing minimal variation in magnetic saturation (Ms) values. Furthermore, we found a time-dependent curve of the transient angle as a function of temperature change, where the angle decreased over time as the particle’s magnetic moments aligned with the direction of the magnetic field. At lower temperatures, the transient angle decreased sharply due to lower dynamic viscosity in the uncured specimen. Hysteresis analysis and time-dependent studies at varying temperatures showed a notable change in curing that occurs at ∼55 °C, indicating the transition from a magneto-rheological fluid to a magnetorheological elastomer. The packing fraction of strontium ferrite particles and saturation magnetization were correlated, while coercivity was field-angle independent and remanence was field angle dependent.
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- Award ID(s):
- 2216440
- PAR ID:
- 10651418
- Publisher / Repository:
- AIP Advances
- Date Published:
- Journal Name:
- AIP Advances
- Volume:
- 15
- Issue:
- 3
- ISSN:
- 2158-3226
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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