Newly developed hygrosensitive poly(vinyl alcohol) derivatives comprising grafted poly(N,N-dimethylacrylamide) chains of varied length and graft density are presented. The optical, sensing, and hydration properties of these copolymer thin films prepared by spin-coating were systematically studied. Refractive indices (n), absorption coefficients (k), and thicknesses (d) were calculated via curve fitting of the reflection spectra. Reflectance measurements across a relative humidity range of 5% to 95% were used to evaluate the humidity sensing behavior. Coating swelling exceeding 100% was observed. Hydration levels under high humidity conditions were studied using a quartz crystal microbalance method. This revealed approximately 24% water content in the polymer with the higher grafting density and shorter PDMA chains compared to around 31% in the copolymer with longer PDMA brushes that were loosely grafted The potential application of these copolymers as responsive materials for advanced humidity sensing is discussed. A combined optical and gravimetric approach for characterizing the humidity sensing properties of thin nanosized coatings is demonstrated, providing opportunities for advanced characterization of new functional materials, thus broadly contributing to the state of the art of sensor technologies.

Thermal annealing improves the mechanical, structural, and electrical properties of polymer thin films, promoting processes like residual solvents and stress removal, as well as the crystallization and densification of the gel layer. The effects are strongly dependent on the annealing temperature, where optimal temperatures enhance film performance, while excessive thermal exposure may induce negative outcomes like amorphous structural transitions, increased roughness, and defect formation. In this work, thin films of two humidity-sensitive poly(vinyl alcohol) (PVA)-based copolymers with grafted poly(N,N-dimethylacrylamide) (PDMA) chains were investigated. The polymers differ in grafting density and chain length, enabling the assessment of macromolecular architecture’s effects. Spin-coated films with 150–200 nm thickness were annealed at three temperatures: 60 °C, 120 °C, and 180 °C. By using UV-VIS-NIR spectroscopy and the quartz crystal microbalance method, a comprehensive characterization of temperature- and humidity-induced changes in swelling, hysteresis, sensitivity, detection resolution, and water uptake is performed, elucidating the role of the macromolecular architecture on the post-deposition annealing modification of gel film properties and its humidity response. High-performance humidity sensing with a resolution of 0.8% RH is achieved through the optimization of the interplay between the macromolecular architecture and annealing temperature. In addition, the study highlights and explores the potential of these films for optical color-based moisture detection.