Magnetorheological(MR) fluid is a smart fluid that changes viscosity characteristics based on surrounding magnetic fields. Generally comprised of a temperature tolerant carrier fluid suspending a specific amount of micron-sized iron particles, this fluid acts in a unique way under magnetic stress, morphing from a honey-like liquid to a viscoelastic near-solid. The malleable rheology of MR fluid is easily exploited for engineering devices, including military body armor, whiplash prevention cushions, and electromagnetic dampers. Increasingly researched and utilized for use in shock-absorbing dampers, MR fluid characteristics allow for almost instantaneous changes in the performance of a device employing such a substance. Dampers, commonly used with oil or gases, compress fluid in a rigid container and allow for a channeled flow that reduces shock while tolerating changes in compression distances. These simple devices are currently used in car suspension systems, bicycle shocks, and even for structural support in large-scale buildings. With the incorporation of MR fluid, such dampers can be effectively tuned with a change in electromagnetic field strength, allowing for quick changes to damper characteristics. This variable damper compression is beneficial for uses ranging from structural earthquake prevention to performance car variable suspension systems. The - characteristics of MR fluid itself, altered by incorporation of specific additives, subsequently alter damper performance.

This project varies concentrations of two additives, silane coupling agent ATPES and thixotropic silica nanoparticles, in an attempt to improve MR fluid characteristics for damper compatibility. A ten-minute mixing of additives and oil precedes a four-hour blending of all MR fluid components, performed at 800 and 500 rpm, respectively. Testing of the fluid batches consisted of a viscosity drops-per-time style test, a shear yield strength test of MR fluid samples sandwiched between two electromagnets, and a seven-day sedimentation test. After testing with 0%, 2%, and 5% APTES-only tests succeeded by 0.25%, 0.5%, and 1% silica with 2% APTES, the 0.5% silica/2% APTES MR fluid displayed optimal sedimentation stability and shear yield strength while maintaining a relatively low zero-field viscosity. To demo damper, a model electromagnetic damper was constructed. In conclusion, addition of APTES and silica nanoparticles significantly increased sedimentation stability and shear yield strength, At 2%APTES/0.5%silica, the MR fluid displayed optimal characteristics for use in a variable compression electromagnetic damper.