Magnetic rotational spectroscopy for probing rheology of nanoliter droplets and thin films

Abstract: In-situ characterization of minute amounts of complex fluids is a challenge. Magnetic Rotational Spectroscopy (MRS) with submicron probes offers flexibility and accuracy providing desired spatial and temporal resolution in characterization of nanoliter droplets and thin films when other methods fall short. MRS analyzes distinct features of the in-plane rotation of a magnetic probe, when its magnetic moment makes full revolution following an external rotating magnetic field. The probe demonstrates a distinguishable movement which changes from rotation to tumbling to trembling as the frequency of rotation of the driving magnetic field changes. In practice, MRS has been used in analysis of gelation of thin polymer films, ceramic precursors, and nanoliter droplets of insect biofluids. MRS is a young field, but it has many potential applications requiring rheological characterization of scarcely available, chemically reacting complex fluids.