Synthesis-controlled magnetic heating in PNIPAm-based nanocomposite gels: role of NaBH4 in particle growth and energy dissipation

Magnetite nanoparticle (MNP)-loaded thermoresponsive poly( N- isopropylacrylamide) (PNIPAm) gels were successfully prepared via in situ formation of MNPs within the polymer network using mixed alkaline solutions containing NaOH and NaBH 4 . The effects of synthesis conditions on nanoparticle formation, crystallite size, thermoresponsive behavior, and magnetic heating performance were systematically investigated. The results showed that the uptake of iron precursor solution and resulting MNP content strongly depended on the Fe 2+ /Fe 3+ concentration ratio, and the optimum composition was 0.1/0.2 mol/L. X-ray diffraction confirmed that crystalline magnetite formed only in the presence of both NaOH and NaBH 4 , whereas NaOH-only systems mainly produced poorly crystalline iron hydroxide species. Increasing the NaBH 4 concentration promoted magnetite formation and crystallite growth, resulting in enhanced magnetic heating under an alternating magnetic field. Based on crystallite size, nanoparticle content, and magnetic heating performance, the optimal NaOH/NaBH 4 ratio was determined to be 0.1/0.1 mol/L. Transmission electron microscopy confirmed the incorporation of relatively well-dispersed MNPs within the gel matrix. Magnetic heating experiments showed that both temperature increase and heating rate (dT/dt) increased with NaBH 4 concentration, although similar heating profiles were observed at 0.10 and 0.20 mol/L NaBH 4 . Despite MNP incorporation, the PNIPAm gels retained their characteristic thermoresponsive volume phase transition around ∼32 °C. These findings demonstrate that the combined NaOH/NaBH 4 system effectively tunes the magnetic heating performance of thermoresponsive PNIPAm gels for applications in magnetic hyperthermia, controlled release systems, and responsive soft materials.