<scp> Fe ₃ O ₄ </scp> ‐enhanced <scp>PVA</scp> /methylcellulose nanocomposite films: A comprehensive study of optical, electrical, thermal, and antibacterial performance

Abstract The design of multifunctional polymer nanocomposites requires a precise understanding of how nanoparticle dispersion governs macroscopic properties. This study demonstrates concentration‐dependent structure–property–function correlations in poly(vinyl alcohol) (PVA)/methylcellulose (MC) blend films (50:50 wt%) reinforced with 2 and 4 wt% Fe 3 O 4 nanoparticles prepared by solution casting. Two distinct dispersion regimes are identified: at 2 wt%, well‐dispersed nanoparticles form isolated micro‐capacitor structures, whereas at 4 wt%, partial agglomeration leads to percolative macro‐capacitor networks. This transition is supported by a shift in the dielectric permittivity peak from 67 °C (blend) to 90 °C (2 wt%) and 75 °C (4 wt%), along with a decrease in Jonscher's exponent from 0.81 to 0.67–0.70, indicating a change from small polaron hopping to correlated barrier hopping. The optical band gap decreases from 4.31 to 3.95 eV with increasing Fe 3 O 4 content, while antimicrobial activity reaches a 4.4 log reduction against S. aureus . These results highlight critical filler loading thresholds governing the transition from polymer‐dominated to filler‐dominated behavior, offering useful insights for the design of multifunctional nanocomposites for antimicrobial coatings, flexible electronics, and energy storage applications. © 2026 Society of Chemical Industry.