Particle organization versus volume fraction in magneto-active elastomer composites

Magneto-active elastomers (MAEs) are a subclass of smart materials that have the ability to actuate and alter their mechanical and magnetic response when subjected to an external magnetic field. Past research has shown that higher net magnetic remanence of an MAE is desirable to increase actuation and produce the most magnetic work. To create a magnetically aligned MAE, a hard magnetic material is mixed in an elastomer solution, then cured in a strong external magnetic field causing particle alignment. A high degree of alignment of magnetic particles is expected to result in improved remanence. However, in MAEs with soft magnetic particles cured in a field, past research has shown that the degree of alignment, vs. less ordered clustering, varies with particulate volume content. Consequently, it is important to study the degree to which volume content of magnetic material affects physical particle alignment, bulk magnetic properties, and the coupling between the two in MAEs with hard magnetic filler particles. In this study MAEs with a hard magnetic filer (barium ferrite) are investigated with varying volume content of magnetic material ranging from 5 to 30% by volume. Batches of MAEs were tested using X-ray diffraction and vibrating sample magnetometry to gain information on crystal structure and bulk magnetic properties. The results of the collected data suggested all poled samples had both higher physical particle orientation as well as a larger remanence than the unpoled counterparts. As volume fraction of magnetic filler was increased the net magnetic properties per volume of magnetic material remained fairly constant. However, the degree of physical particle orientation varied with a local minimum at medium volume fractions. Collected data was used to calculate two orientation parameters, the degree of preferred alignment parameter, η, and the orientation of distributions of magnetic domains parameter, σ. The two parameters were compared to show a relationship between physical particle alignment and net magnetic properties as volume of magnetic material increases. Based on the collected results, a hypothesis is presented on how particle interaction is speculated to evolve as volume fraction of magnetic material is increased.