Computational Study of the AC Susceptibility of Isolated Magnetic Nanoparticles in a Polymer Suspension

Magnetic nanoparticles immersed in polymeric environments are promising candidates for both technical and bio-medical applications. Unfortunately, in many such systems the details of the coupling mechanisms are still unknown. Experimentally, the magnetic properties are typically studied using frequency-dependent AC susceptibility measurements from which also elastic properties of the surrounding polymer suspension can be inferred using appropriate theory such as the Gemant-DiMarzio-Bishop model [DiMarzio and Bishop, J. Chem. Phys., 1974, 3802–3811]. We present a computational study of isolated magnetic nanoparticles in a polymer suspension, considering only hydrodynamic and excluded volume interactions. AC susceptibility spectra are extracted using a linear-response Green-Kubo approach. We show that hydrodynamic coupling to the rotational behavior of the nanoparticles alone can lead to shifts of the spectra towards lower frequencies with both, increasing polymer concentration and polymer chain length. These findings qualitatively reproduce recent experimental observations [Roeben et al., Colloid Polym. Sci., 2014, 2013–2023].

[Kreissl, Holm and Weeber, Soft Matter, 2020]