Stability and activity of the polydopamine coating over time

Abstract

The aim of this study was to assess the stability of polydopamine coatings over time and to determine the influence of the substrate type on their physicochemical properties. Polydopamine coatings were deposited on soda-lime glass, cellulose paper, and polycarbonate. The stability of the coatings was evaluated after one, two, and four weeks of conditioning using FTIR spectroscopy, SEM microscopy, EDS microanalysis, and contact angle measurements. The analyses revealed that polydopamine effectively covers the examined surfaces; however, its structure and uniformity depend on the substrate. On glass and polycarbonate, the coating formed a compact layer, whereas on paper, it developed a striated structure covering the cellulose fibers. Over time, a gradual decrease in nitrogen content in the surface layer was observed, suggesting polydopamine degradation, likely influenced by UV radiation. Contact angle measurements showed changes in coating hydrophilicity, which gradually returned to values characteristic of uncoated substrates over time. The reducing activity of polydopamine in silver deposition from an aqueous solution decreased by 40–60 % over time. Therefore, the study demonstrated that polydopamine stability depends on the substrate and storage conditions. UV radiation limits polydopamine activity, which should be considered for potential applications of the deposited coating.