Frontal Polymerization Synthesis and Humidity Sensing Properties of Pd-Doped Polyacrylamide with Theoretical Validation using DFT

In this paper, the frontal polymerization synthesis of Pd-doped polyacrylamide has been reported. A thin film based on this material is fabricated for characterization purposes as well as for humidity sensing. For material characterization, Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX) spectroscopy, Particle Size Analyzer, UV-visible spectroscopy, X-ray diffraction (XRD), and Fourier Transform Infrared (FTIR) spectroscopy techniques are used. FESEM shows that the synthesized polymer is porous. The EDX spectrum confirms the presence of constituent elements in the metallopolymer. The particle size analyzer shows that the synthesized polymer has a particle size in the nano range. Pd-doped polyacrylamide has a 5.3 eV optical band gap of energy. After characterization, the polymer is employed for humidity sensing, and the sensor shows 2.01 MΩ/%RH, 96.52% and 5 and 40 s sensitivity, repeatability response and recovery times, respectively. A theoretical framework was established to elucidate the humidity-sensing mechanism of Pd-doped polyacrylamide. Density functional theory (DFT) calculations provided detailed insights into the structural and electronic modifications induced by H ₂ O adsorption. The simulated electronic responses, including band gap modulation and charge redistribution, exhibit strong agreement with experimental observations, thereby validating the proposed sensing mechanism and confirming the reliability of the theoretical model.