Structure–property relationships in magnetic PNIPAm microgel nanocomposites for enhanced heating performance

Polymer microgels incorporating magnetic nanoparticles (MNPs) were synthesized, and their structural characteristics and magnetic heating behavior were systematically examined. Initially, the formation of polymer microgels was optimized by assessing the effects of polymerization parameters, including polymerization temperature and the concentrations of monomer, crosslinker, and initiator, on the particle size distribution (PSD) of the microgels. These parameters significantly influenced the nucleation and growth of the microgel particles, facilitating the preparation of microgels with controlled sizes and relatively narrow size distributions. Subsequently, MNPs were generated in situ within the microgels through the coprecipitation of Fe 2+ and Fe 3+ ions. The effects of synthesis parameters on nanoparticle formation were investigated by varying the concentrations of iron ions (FeCl 2 and FeCl 3 ), sodium hydroxide (NaOH), and sodium borohydride (NaBH 4 ). Transmission electron microscopy and PSD analyses demonstrated that these parameters strongly affect the nucleation and growth of MNPs within the polymer network. In particular, increasing the NaBH 4 concentration promoted the formation of larger MNPs and broadened the PSD. Finally, under optimized conditions for iron ion and NaOH concentrations, the influence of NaBH 4 concentration on the magnetic heating behavior of MNP-loaded microgels was evaluated under an alternating magnetic field. The temperature rise increased with increasing sample mass, indicating that heat generation depends on the amount of magnetic material. Moreover, differences in heating performance were observed even at similar MNP masses, suggesting that particle size and PSD influence magnetic relaxation processes and heat generation efficiency.