Remote Sensing of the Nano-Rheological Properties of Soft Materials Using Magnetic Nanoparticles and Magnetic AC Susceptometry.

We have developed a nano-rheological characterization tool to extract the frequency- and scale-dependent rheological properties of soft materials during oral processing. Taking advantage of AC susceptometry, the dynamic magnetization of magnetic nanoparticles blended in the matrix material is measured. The magnetic AC susceptibility spectra of the particles are affected by the viscosity and mechanical modulus of the matrix material and provide the rheological properties of the matrix. Commercially available iron-oxide magnetic nanoparticles with 80 and 100 nm particle sizes are used as tracers in the frequency range of 1 Hz-10 kHz. The AC susceptibility is measured using two differentially connected coils, and the effects of the sample temperature and distance with respect to the detection coils are investigated. The developed measurement setup shows the feasibility of remote nano-rheological measurements up to 2 cm from the coil system, which can be used to, e.g., monitor the texture of matrix materials during oral processing.