Rheology-Assisted Microstructure Control for Printing Magnetic Composites—Material and Process Development

Abstract

Magnetic composites play a significant role in various electrical and electronic devices. Properties of such magnetic composites depend on the particle microstructural distribution within the polymer matrix. In this study, a methodology to manufacture magnetic composites with isotropic and anisotropic particle distribution was introduced using engineered material formulations and manufacturing methods. An in-house developed material jetting 3D printer with particle alignment capability was utilized to dispense a UV curable resin formulation to the desired computer aided design (CAD) geometry. Formulations engineered using additives enabled controlling the rheological properties and the microstructure at different manufacturing process stages. Incorporating rheological additives rendered the formulation with thixotropic properties suitable for material jetting processes. Particle alignment was accomplished using a magnetic field generated using a pair of permanent magnets. Microstructure control in printed composites was observed to depend on both the developed material formulations and the manufacturing process. The rheological behavior of filler-modified polymers was characterized using rheometry, and the formulation properties were derived using mathematical models. Experimental observations were correlated with the observed mechanical behavior changes in the polymers. It was additionally observed that higher additive content controlled particle aggregation but reduced the degree of particle alignment in polymers. Directionality analysis of optical micrographs was utilized as a tool to quantify the degree of filler orientation in printed composites. Characterization of in-plane and out-of-plane magnetic properties using a superconducting quantum interference device (SQUID) magnetometer exhibited enhanced magnetic characteristics along the direction of field structuring. Results expressed in this fundamental research serve as building blocks to construct magnetic composites through material jetting-based additive manufacturing processes.

Development and Characterization of Field Structured Magnetic Composites

“…The photograph in Figure 4 shows a single deposited layer on an acrylic sheet substrate. Note that UV curing of the deposited layer in conjunction with particle alignment using the magnetic array was accomplished using ‘manufacturing scenario B’ established in a previous publication by the present authors [ 35 ]. In summary, the process step for each layer involves (i) material deposition, (ii) magnetic particle alignment for a set time, and (iii) UV exposure for 60 s. The photographs in Figure 5 show the material jetting equipment with the in-situ particle alignment system and the UV source for subsequent curing.…”

“…Differences in the apparent degree of particle alignment and stacking between sample S2 and S3 in Figure 9 are likely related to the prepolymer viscosities. From previous research it is known that the viscosity of the acrylate-based prepolymer is approximately 0.3 Pa·s whereas the value for the epoxy resin is 7 Pa·s [ 20 , 35 ].…”

“…It should be mentioned that for the S1 sample the magnetic particle alignment time was shorter than for the samples produced by polymer casting. Adjusting the alignment time for 3D printed samples was necessary to mitigate material deformation under the influence of the magnetic field because no mold is providing material containment in this case (as discussed in [ 35 ]).…”

“…XRD analysis was conducted only for sample S2 and an additional isotropic sample fabricated using epoxy as the base prepolymer. In the presence of a magnetic field, a magnetic moment is generated along the easy axis of magnetization which results in particles interacting and forming aligned microstructures [ 35 ]. First, the magnetic powder was characterized to identify and confirm the chemical composition.…”

Process–Structure–Properties in Polymer Additive Manufacturing

“…Abdolmaleki and Agarwala looked into using polyvinylidene difluoride added with barium titanate (PVDF–BaTiO 3 ) for printed electronics [ 7 ]. Nagarajan et al explored a methodology for the manufacture of magnetic composites using an in-house developed material jetting AM machine [ 8 ]. Sahay et al demonstrated the use of a parallel plate for electrospinning-based AM in the fabrication of helicoidally arranged polyacrylonitrile fibre-reinforced polyvinyl alcohol polymer thin films [ 9 ].…”