Effect of Phase Transitions in Polymer Solutions on the Magnetic Response of Embedded Nanoparticles

Doping complex polymer solutions with magnetic nanoparticles opens up a class of functional materials. However, a distinct decrease in the degree of magnetic in-field alignment of nanoparticles upon crystallization of the carrier liquid is observed, which could pose a crucial hindrance for the preparation of such hybrid materials. To understand their behavior in detail, including their performance over extended temperature ranges and their structural transformations in the presence of external fields, it is useful to employ direct methods that provide information on the particle length scale. Here, we aim to understand the quasi-static magnetic behavior of magnetic particles in complex fluid environments employing aqueous solutions of poly­(ethylene glycol) as model systems and discuss their thermomagnetic behavior under the influence of phase transitions. For this purpose, magnetically blocked nanoparticles based on cobalt ferrite (CoFe₂O₄) are utilized as tracer particles in temperature-dependent magnetization measurements complemented by differential scanning calorimetry (DSC). Following this approach, a detailed understanding of the impact of thermal phase transitions such as (eutectic) melting and freezing as well as glass transitions on the mobility of the particles is obtained at different concentration regimes.