Predicting the Alignment of Ferromagnetic Particles in a Thermoplastic Matrix

Abstract

This study investigates the use of an external magnetic field to cause the magnetic and physical alignment of ferromagnetic particles in a thermoplastic polymer matrix. The composite selected provides the best alignment involving rare-earth ferromagnetic particles in a polystyrene matrix. The rare-earth particles are able to be effectively aligned due to their high magnetic and physical anisotropy. The time-to align the particles ranged from <5 s at 498 K to approximately 60 s at 398 K. Composites with weight percents ranging from 5 to 25% are studied. A model is developed in order to predict the alignment, and is validated against experimental data. This model predicts the time-to-align based on magnetic torque balancing that would cause alignment with the viscous drag that acts to slow the particle rotation. It is found that the model describing the polymer as a Newtonian fluid follows the same trends and form as the experimental data. Potential sources of differences that prevents close fit to the data are attributed to particle interactions, sample variations, and especially the shear thinning behavior of polystyrene.