Surface characterization of polymeric coatings in icing environments and process optimization of spray-coated silica-based films

Formation and adhesion of ice on exposed surfaces pose major challenges in several technological fields, from aeronautics to infrastructures operating in cold environments. The development of coatings able to delay or prevent ice formation, or to facilitate its removal, requires a deep understanding of the mechanisms governing ice nucleation and growth at solid-liquid interfaces, as well as the physical and chemical properties of the coating materials. This thesis investigates two complementary approaches to surface modification aimed at improving the anti-icing performance of materials: the study of the ice nucleation behavior on polymeric coatings containing charged or hydrophilic functional groups and the fabrication and process optimization of silica-based hybrid coatings deposited by spray-coating. In the first part, methacrylate copolymers with varying ratios of crosslinker (B), comonomers (BM, H) and active group (PM) were synthesized and applied as thin films. Their wettability was characterized through static contact angle and surface energy measurements at different temperatures (25°C to -5°C), while climatic chamber tests quantified the freezing probability of water droplets at -9°C in 300 seconds’ time. The results showed that copolymers with higher polar content (PM50H40B10) accelerated ice nucleation due to increased water-surface interactions, while those with higher butyl methacrylate (PM25BM70B5) fractions displayed delayed freezing, confirming the impact of hydrophobic side chains in limiting hydrogen bonding. The observed freezing behavior followed an exponential trend consistent with stochastic heterogeneous nucleation models. The second part focused on the optimization of a TEOS-MTES derived silica coating (MTO) prepared through sol-gel method. The films were deposited by both dip and spray coating and subjected to thermal curing at different temperatures. FTIR spectroscopy confirmed the formation of Si-O-Si networks, while dynamic contact angle measurements revealed increasing hydrophobicity after hotplate consolidation, especially 15 minutes at 200°C, with hysteresis low to 25°. Mechanical characterization indicated strong tape adhesion (3B to 4B) and high surface hardness (up to 6H) by pencil test, particularly in spray-coated multilayer systems (5, 8 and 11 layers). Optical microscopy and profilometry showed a progressive reduction in surface roughness with layer number, suggesting film leveling rather than simple thickness accumulation.