Effect of carbon quantum dots on the UV-curing behavior and properties of waterborne polyurethane acrylate coatings

Photoactive carbon quantum dots (CQDs) are promising modifiers for waterborne polyurethane acrylate (WPUA) coatings, but their effect on UV-curing kinetics depends on how they interact with the photopolymerizable matrix. This study evaluates the influence of CQDs surface chemistry, photoluminescence quantum yield (QY), and incorporation route on curing behavior and final coating properties. Two CQDs with distinct QY values (≈23% and ≈62%) but similar surface functional groups were incorporated into WPUA dispersions via aqueous-phase addition and acetone pre-dispersion. Photo-DSC analysis revealed that CQDs broadened curing profiles, increased peak time from 4.2 s to 13.7–44.5 s, and reduced C=C conversion from 92.8% to 50.8–77.9%. A semi-quantitative analysis indicated that curing retardation arises from combined competitive UV absorption and route-dependent mobility restrictions induced by CQDs–WPUA interactions. Despite reduced conversion and gel content (97.8% to 83–93%), CQDs improved coating performance, increasing tensile strength from 4.3 MPa to 6.1–6.6 MPa (≈40–53%), and thermal stability (T 10% ) from 298.2 °C to 309.1 °C. The incorporation route affected curing and properties in a CQDs-dependent manner, while QY differences produced only minor kinetic effects, indicating that surface chemistry and matrix interactions govern the response more strongly than photoluminescence. Under air, selected formulations suggested an apparent attenuation of oxygen inhibition, consistent with auxiliary CQDs photoactivity. Hansen solubility parameter analysis further revealed a contraction of the solubility sphere, indicating a more constrained network with improved solvent resistance. CQDs act as multifunctional modifiers that tune curing efficiency and coating performance through surface functionality and incorporation route.