Videos of Magnetorheological suspensions response under continuous frequency sweeping

Self-assembly of magnetic colloidal particles into pre-programed microstructures plays an important role in the design of functional soft materials of interest in the microfabrication of sensors, actuators and/or tissue engineering applications. Particle aggregates emerge because of a delicate balance between magnetic interparticle interactions and hydrodynamic interactions with the carrier. These aggregates are dynamic and follow the field when its frequency is small enough. However, for sufficiently large field frequencies the particles within the aggregates experience a time-averaged magnetic interaction that results in the formation of static (i.e. arrested) gel-like structures. The transition between the dynamic and static state is not well understood because strong fields are needed to continuously vary their frequency in a wide range. Current approaches, that involve the use of capacitors, require to periodically turn off the field generation disrupting the gel-like structure. In this manuscript, we propose the use of an inductance approach to work at the resonance that does not require switching-off periods during the frequency sweep. Moreover, both videomicroscopy and rheometry are used to monitor the microstructure and rheological properties under oscillatory shear. Field interruptions lasting more than 20% of duty ratio have been shown to alter rheological measurements.