RUI: Systematic Study of the Rheology and Sedimentation of Microwire-Based Magnetorheological Fluids

CBET-0755696

Bell

Conventional magnetorheological (MR) fluids consist of spherical micron-sized ferromagnetic particles suspended in a carrier fluid. These suspensions are converted from a viscous liquid to a semi-solid with the application of a magnetic field. The viscosity and apparent yield stress of the suspensions are controlled by varying the strength of the external magnetic field. However, a major drawback to common use of these composite materials in many applications is particle sedimentation that requires re-dispersion of the particles, which causes unfavorably lengthy response times. Current additives meant to limit sedimentation result in a diminished yield stress at comparable magnetic fields. In this study, The PIs investigate the rheology, sedimentation, and magnetic properties of unconventional microwire-based MR fluids employing cylindrical particles with aspect ratios ranging from 3 to 100 suspended in silicone oil and dimorphic suspensions that contain a mixture of spherical and microwire particles. Using template-based electrodeposition, The PIs fabricate pure ferromagnetic microwires with controllable diameters ranging from 260 to 320 nm and lengths in the range of 1 to 30 microns. For a variety of fluid compositions and magnetic field strengths, the shear stress will be measured as a function of shear rate and the results modeled using various constitutive models to determine the apparent yield stress, viscosity and other viscoelastic properties as a function of increasing volume fraction and particle geometry and composition of these microwire-based suspensions. A finite-element, multiphysics simulation package will construct basic simulations of these suspensions to examine the role of particle shape, aspect ratio, magnetic properties, and particle concentration on the sedimentation and magnetorheology of these suspensions. Establishing the magnetorheology of microwire suspensions will be a significant move forward in the understanding and application of MR fluids. Preliminary studies are promising; pure microwire MR fluids display a significantly decreased amount of settling as compared to conventional MR fluids when only a few volume percent of the spheres are replaced with microwires. The broader impact of these studies is twofold. First, properties of a novel magnetorheological fluid that displays reduced sedimentation while maintaining enhanced yield stress will be provided. This knowledge will have the potential to broaden the application of MR fluids, paving the way for a variety of new applications that could be transferred to the industrial sector directly. The knowledge about the magnetic properties of the wires gained from these studies may also prove useful in applications such as magneto-optical and microwave devices. Second, this project will provide for training and development of undergraduate and high school students, promote the professional development of faculty, and encourage participation by individuals belonging to groups underrepresented in the sciences. Undergraduate students will receive significant experience and training as they fully participate in the synthesis, characterization, testing, and modeling of the MR fluids and the dissemination of results. Since the work involves collaborators at the Materials Research Institute (MRI) at Penn State and at the University of Maryland, our undergraduate researchers will have the opportunity to communicate with other students and faculty at these institutions.