Dynamics of magnetic nanoparticles in viscoelastic media

We compare different models for the description of the complex susceptibility of magnetic nanoparticles in an aqueous gelatin solution representing a model system for a Voigt-Kelvin scheme. The analysis of susceptibility spectra with the numerical model by Raikher et al. [7] is compared with the analysis applying a phenomenological, modified Debye model. The fit of the models to the measured data allows one to extract the viscoelastic parameter dynamic viscosity. and shear modulus G. The experimental data were recorded on single-core thermally blocked CoFe2O4 nanoparticles in an aqueous solution with 2.5 wt% gelatin. Whereas the dynamic viscosities obtained by fitting the model - extended by distributions of hydrodynamic diameters and viscosities - agree very well, the derived values for the shear modulus show the same temporal behavior during the gelation process, but vary approximately by a factor of two. To verify the values for viscosity and shear modulus obtained from nanorheology, macrorheological measurements are in progress.