UV-curable polymer coatings are emerging as green alternatives for different applications due to their fast curing rates, low volatile contents (VOCs), and energy efficiency. However, inherent brittleness, absence of reparability, and static surface characteristics limit their functional adaptability. Herein, we introduce a novel UV-curable, multifunctional, gradient crosslink density nanocomposite coating system that combines in-situ UV-induced self-healing, tunable surface wettability, and mechanical enhancement, which are achieved without encapsulated agents or sacrificial layers. Our design uniquely integrates a dual-oligomer matrix of urethane acrylate and bisphenol-A ethoxylate dimethacrylate, plasticized with 1,6-hexanediol diacrylate for sub-glass transition temperature (Tg) flexibility. A binary photoinitiator system (Darocur 1173 and Omnirad TPO) enables a more crosslinked, dense surface network structure due to the former initiator (to promote mechanical robustness), and a less crosslinked (more flexible) deep-film network structure due to the latter initiator (to promote adhesion to the substrate) under UV-A/B. Overall, a gradient crosslink density coating structure is achieved. As the second objective of this work, novel functionalities are imparted to the coatings through synergistic inclusion of phosphorus-doped graphene, promoting radical diffusion, thermal conductivity, and flame retardancy, and acrylated polyhedral oligomeric silsesquioxane (POSS), facilitating UV-induced surface reorganization, water repellency, and impact resistance. It is hypothesized that the inclusion of these two nanofillers will modify the network structure, which will be fully investigated herein. Optical profilometry and nanoindentation revealed partial mechanical recovery post-UV re-exposure, validating photo-triggered self-healing for the neat coating. Contact angle goniometry was used to measure changes in surface wettability, while flame retardancy was assessed using a Limiting Oxygen Index (LOI) test. Gradient crosslink density was characterized using peak-force atomic force microscopy (AFM). Mechanical and thermal properties were thoroughly examined using dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). This study explores a UV-processable, nanoreinforced smart coating that exhibits healing capability, tunable wettability, and improved structural resilience within a solvent-free platform. Ongoing efforts are directed toward assessing its cyclic durability and modeling interfacial behavior with metal and cement substrates to better understand its potential for long-term protection.
