Abstract
Composites of magnetite (Fe3O4) nanoparticles dispersed in a polydimethylsiloxane (PDMS) matrix were prepared by a molding process. Two types of samples were obtained by free polymerization with randomly dispersed particles and by polymerization in an applied magnetic field. The magnetite nanoparticles were obtained from magnetic micrograins of acicular goethite (α-FeOOH) and spherical hematite (α-Fe2O3), as demonstrated by XRD measurements. The evaluation of morphological and compositional properties of the PDMS:Fe3O4 composites, performed by SEM and EDX, showed that the magnetic particles were uniformly distributed in the polymer matrix. Addition of magnetic dispersions promotes an increase of thermal conductivity compared with pristine PDMS, while further orienting the powders in a magnetic field during the polymerization process induces a decrease of the thermal conductivity compared with the un-oriented samples. The shape of the magnetic dispersions is an important factor, acicular dispersions providing a higher value for thermal conductivity compared with classic commercial powders with almost spherical shapes.
Highlights
We examine the thermal conductibility of the composites with two types of magnetite randomly dispersed particles in a PDMS matrix and the influence of applying a magnetic field to modify the particle arrangement on the thermal properties of the composite materials
The samples obtained by free polymerization display a good packaging structure, with a homogeneous distribution of the magnetite grains in the PDMS matrix and very small pores (Figure 5a,c)
We demonstrated how thermal conductivity of composite materials can be influenced by the orientation of the magnetite added into the polymer matrix
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Composites of magnetic nanoparticles randomly dispersed in a polymer matrix are promising materials widely applied in many engineering areas for magnetic separation, catalysis, MRI contrast agents, or electromagnetic shielding [1,2,3,4,5]. Polydimethylsiloxane (PDMS) is a suitable polymer for embedded composite materials that combine the properties of the matrix and the nanoparticles [6,7,8]. In the early stage of electromagnetic actuator evolution, the actuator was designed by incorporating a bulky permanent magnet placed on the top of the deforming membrane [9]. Thin silicon membrane was used as actuator membrane [10,11]
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