Temperature Dependent Magnetic Properties of Polydimethylsiloxane/SrO(Fe₂O₃)₆Composite Measured by Biaxial VSM

Composites made of magnetic particles embedded in a flexible polymer are being studied for application in soft actuators. Due to their strength, thermal stability, and chemical resistance, thermoset composites will be essential for the development of the upcoming medical, engineering, aerospace, robotics, marine, and energy applications. Here, we study the curing of Polydimethylsiloxane (PDMS) thermoset polymer and SrO(Fe₂O₃)₆ powders. Two different compositions (20.0wt% and 33.3wt% powder) were prepared by hand mixture and transferred to an Ultem sample holder for magnetic characterization in a vibrating Sample Magnetometer (VSM). Hysteresis loops and time dependent analysis were performed at different temperatures to study the curing process. The suspension shows a drastic change in hysteresis as the material changes from a magneto-rheological fluid to a magnetorheological elastomer around 55 °C indicating the significant curing. The saturation magnetization (Ms) scales with packing fraction. While the coercivity (Hc) is independent of the field angle, Mr varies as a function of the field angle indicating the existence of magnetic anisotropies in the field cured samples. The rotation of the magnetic particles in a step field of 250 Oe was determined from time-dependent measurements and shows that it takes more time to align them after longer annealing periods at higher temperature. This results from an increase in viscosity due to cross linking during the curing process.