Novel superhydrophobic polysiloxane-based materials for the conservation of marble

Abstract

Abstract: Biomimetic materials with extreme wetting properties (MEWP) offer great potential as protective coatings against water-induced damage and oil-based soiling of stone-built heritage. This thesis assessed the performance of two novel coatings, one superhydrophobic, D/S/F (WCA =160.0°), and the other superamphiphobic, 6P/1F/2S (WCA=160.3°, OCA=152.2°). This involved characterizing their wettability, breathability, mechanical durability, resilience to environmental degradation agents (extreme temperature, acid/ rain, particulate matter) and response to accelerated UV-aging. Test protocols were adopted from standards, adapted from previous research, and optimized through trial runs. Particularly, the sandpaper abrasion test was applied to coatings being developed for heritage application for the first time. The D/S/F coating showed a 25% improved protection from water uptake compared to the commercial product with minimal effect on breathability (%RVP = 16%). It also demonstrated great mechanical durability across many cycles of sandpaper abrasion, tape peeling, acid rain simulation and sand-grit erosion. The 6P/1F/2S coating, however, did not offer improved protection from water penetration, with a higher associated impact on the breathability of stone (%RVP = 54%) but showed promising tolerance to freeze-thaw cycles and acid/rain simulation. Both the coatings maintained enhanced hydrophobicity over 2 months of artificial UV-aging. In summary, this research delineates the performance of two novel coatings displaying extreme wetting behaviour, while also contributing towards the development of test protocols that enable application-oriented assessment of coatings designed for the protection of stone heritage.