Poly(N-isopropylacrylamide) nanoparticles for QCM-based gas sensing of HCl

Poly(N-isopropylacrylamide) (PNIPAM) nanoparticles were prepared by precipitation polymerization using atom transfer radical polymerization (ATRP) in aqueous media at 45 °C, which is above the lower critical solution temperature (LCST). Nanoparticles were coated on a quartz resonator and their HCl gas-sensing properties were measured by a quartz crystal microbalance (QCM) technique. PNIPAM nanoparticles adsorbed HCl gas reversibly, while PNIPAM thin film showed partly irreversible adsorption. Furthermore, for PNIPAM nanoparticles, the gas adsorption/desorption properties, such as adsorption time and reversibility, were not influenced by the mass loaded on the quartz resonator, which indicated that these properties were derived from the sum of the properties of each individual nanoparticle. The QCM-based PNIPAM nanoparticle sensor showed excellent reproducibility and the sensitivity to 1 ppm of HCl was approximately 3.8 Hz/ppm.