The Governing Role of Polymer Matrix in Tailoring the Functional Properties of Magnetite‐Filled Nanocomposites

ABSTRACT This study presents a systematic comparative investigation of Fe 3 O 4 ‐loaded thermoplastic nanocomposites synthesized using a unified protocol across four matrices: polypropylene (PP), polyethylene (PE), polyvinylidene fluoride (PVDF), and polyvinyl chloride (PVC) at nanoparticle loadings of 1–10 wt%. Structural analysis confirmed the formation of crystalline Fe 3 O 4 in all systems. PVDF exhibits the α‐to‐β phase transformation, as evidenced by the disappearance of the 2 θ = 18.4° peak. The enhancement at 20.8° is indicative of the induction of the electroactive β‐phase. Thermogravimetric analysis revealed matrix‐dependent degradation profiles of the nanocomposite. The effect of Fe 3 O 4 nanoparticles on the thermal stability of PVDF, PP, PE, and PVC polymer matrices was evaluated based on TGA analysis. The results showed that the addition of Fe 3 O 4 increased the temperature corresponding to all stages of degradation in PP and PE polymers, thereby increasing their thermal stability. In contrast, in PVDF+5%Fe 3 O 4 and PVC+5%Fe 3 O 4 systems, only the temperature corresponding to 50% mass loss was higher than that of the host polymer. For these nanocomposites, the temperature corresponding to initial and final mass loss was shifted toward lower temperatures with respect to the host polymer, which is explained by the catalytic effect of the nanoparticles in these polymers. Dielectric measurements demonstrated maximum permittivity ( ε ') increases of up to 6× for PVDF and 3× for PE at 1 kHz, with strong Maxwell–Wagner–Sillars dispersion observed in polar matrices. Spectroscopic ellipsometry analysis showed that at 1.5 eV photon energy, the extinction coefficient changes as follows, depending on host polymer: k PP ≈0.25 > k PE ≈0.19 > k PVDF ≈0.13 > k PVC ≈0.08. The maximum value of the refractive index ( n ) was observed for PP‐based nanocomposites at 6.5 eV. These findings quantitatively support the idea that matrix polarity, crystallinity, and interfacial compatibility critically govern thermal stability, dielectric performance, and optical properties in Fe 3 O 4 ‐filled nanocomposites. The PP‐based nanocomposites showed the highest optical and thermal performance, while PVDF offered dielectric tunability. These materials possess high potential in EMI shielding, photothermal systems, and dielectric devices.