Spray-coating fabrication of silica-based films through the optimization of a polydopamine primer layer

The aim of this work is to develop stable spray coated silica films through the optimization of a polydopamine (PDA) primer layer. The deposition process was first optimized by investigating the influence of deposition method, substrate temperature, dopamine solution aging duration and solvent composition on the morphology of the PDA coating. Subsequently, silica nanoparticles synthesized from TEOS and TEOS/MTES precursor mixtures were spray deposited onto the optimized primer layer and characterized in terms of morphology, wettability and mechanical duration. The results showed that spray coating produced more homogenous PDA films than conventional immersion deposition. Among the investigated deposition conditions, a substrate temperature of 120 °C, freshly prepared dopamine solution and ethanol/water solvent system resulted in the most uniform primer morphology. Silica coatings deposited on the optimized PDA layer exhibited improved surface homogeneity compared to coatings deposited on bare silicon substrates. Among the investigated compositions, TEOS/MTES 1:2 coating showed the most homogeneous morphology and the highest static contact angle (122°). Mechanical characterization demonstrated good stability, achieving 4B classification in the cross cut tape test and a progressive increase in pencil hardness with increasing MTES content. The optimized PDA primer layer significantly improved coating stability. However the relatively thin primer layer and the resulting coating were not sufficient to achieve high mechanical robustness. Further optimization is still required.