DF-11 Magnetic Field-Induced Thermal Behavior and Sedimentation of Strontium Ferrite-PDMS Composites for Actuator Applications

Abstract: Magnetic composite polymers combine the properties of both magnets and polymers, which enables the production of complex-shaped magnetic components. These materials have potential applications ranging from microfluidics to vibration dampers, actuators, and minimally invasive medical devices because, with an applied magnetic field, they can change shape precisely, quickly, and consistently. Our study investigates the dispersion of strontium ferrite particles (SrO(Fe2O3)6) suspended in the polydimethylsiloxane (PDMS) matrix and how that is effected by gravity, an applied magnetic field, or vacuum. The time-dependent behavior of composites in a magnetic field during the curing process was also explored. Particle density and orientation in the cured composite were determined from hysteresis curves measured with a MicroSense EZ9 VSM. A punching tool was used to take samples from a 40-mm-long cylindrical sample. We found well-distributed strontium ferrite (SF) particles in PDMS when curing the composite without a magmatic field. However, during curing in the presence of a magnetic field provided by a Halbach cylinder, the particles align along the field lines, leaving a clear SF particle-depleted PDMS layer on the surfaces. A similar effect was observed when the suspension was cured in vacuum, while very little sedimentation due to gravity was reported. Furthermore, the time-dependence of the magnetic moment vector in an applied magnetic field during the curing process was measured using the method of Ahmed [1]. The magnetic moment transient as a function of curing time and temperature was measured with the biaxial VSM. At lower temperatures, the transient had a small time constant due to the lower dynamic viscosity of the uncured specimen. Hysteresis analysis and time-dependent studies after various temperature treatments showed a notable change in curing at approximately 55 °C, indicating the transition from a magneto-rheological fluid to a magnetorheological elastomer. The fraction of SF particles and saturation magnetization were correlated, while coercivity was field-angle independent and remanence was field-angle-dependent. This work was in part supported by NSF (grant 2216440).References: [1] Tanjina N. Ahmed et al. AIP Adv. 13, 025024 (2023).