Facile preparation of graphene oxide/Poly (N-Isopropylacrylamide-co-acrylic acid) composite thin film and its quartz crystal microbalance humidity sensing property

The composite microgels were synthesized from N-Isopropylacrylamide (NIPAM) and acrylic acid (AA) monomers in the presence of graphene oxide (GO) using an in situ radical copolymerization method. The successful preparation of these composite microgels was investigated through Fourier transform infrared spectroscopy (FTIR), ultraviolet visible absorption spectroscopy (UV–vis), and Raman spectroscopy. Due to the hydrophilic properties of GO and the microgels containing oxygenated groups (OH, COOH, and CONH₂), quartz crystal microbalance (QCM) sensors can be fabricated by spraying the GO/P(NIPAM-co-AA) dispersion onto QCM sensors as sensitive coating materials. The results indicate a notable enhancement in the performance of GO/P(NIPAM-co-AA) modified QCM humidity sensor, compared to QCM sensors modified with either GO or P(NIPAM-co-AA) microgels alone. This improvement is mainly evidenced by higher sensitivity and reduced moisture hysteresis. The humidity sensing mechanism is based on the combined effect of GO and P(NIPAM-co-AA) microgels, which synergistically enhance the sensor's performance. Additionally, the results from water contact angle measurements, laser scanning confocal microscopy (LSCM), and scanning electron microscope (SEM) show that GO/P(NIPAM-co-AA) exhibits greater roughness and stronger hydrophilicity than either GO or P(NIPAM-co-AA) microgels alone. These properties make GO/P(NIPAM-co-AA) an effective moisture-sensitive material for QCM sensors.