Silane-based materials are used for the protection of heritage and modern buildings. A versatile method is developed to tune the wetting properties of a typical silane-based material from hydrophobicity to superamphiphobicity, thus enhancing the protective efficacy against rainwater and organic pollutants. A commercially available silane product is blended with a fluoropolymer to lower the surface energy and silica (SiO₂) nanoparticles to affect the surface morphologies of the produced coatings on marble. Contact angles of water and oil drops are measured on the coating surfaces which were prepared using 16 different combinations of fluoropolymer and nanoparticle concentrations. It is shown that the synergistic effect of surface structure and chemistry can lead to the production of coatings that possess superamphiphobic properties. The wetting properties of a selected non-wettable coating are further characterised using a custom-made, fully-automated device (Kerberos) which monitors simultaneously the deformation of the liquid interface, spreading and sliding of the drop along the sample surface during tilting. Several tests are carried out to evaluate the durability of the selected superamphiphobic coating, offering overall promising results. The versatile method can be used to impart superamphiphobicity to the surfaces of various materials. The method developed herein can be adopted to tune the wetting properties of other silane-based commercial products which are used for the protection of buildings.

The erosion phenomena of the natural stone in cultural heritage are induced by various sources. Consequently, the development of multifunctional protective materials that combine two or more useful properties is an effective strategy in addressing the synergistic effects of various erosion mechanisms. A multifunctional coating, consisting of a silane-based precursor and zinc oxide (ZnO) nanoparticles (NPs), is produced and tested for the protection of limestone. The hybrid coating combines the following three properties: superhydrophobicity, including water-repellency, photocatalytic self-cleaning and biocidal activity. The relative concentration of the NPs (0.8% w/w), used for the suggested composite coating, is carefully selected according to wetting studies, colourimetric measurements and durability (tape peeling) tests. The non-wetting state is evidenced on the surface of the composite coating by the large contact angle of water drops (≈153°) and the small contact angle hysteresis (≈5°), which gives rise to a physical self-cleaning scenario (lotus effect). The photocatalytic chemical self-cleaning is shown with the removal of methylene blue, induced by UV-A radiation. Moreover, it is shown that the suggested coating hinders the incubation of E. coli and S. aureus, as the inhibitions are 94.8 and 99.9%, respectively. Finally, preliminary studies reveal the chemical stability of the suggested coating.

Wood, a vital material for both modern and heritage objects, is particularly susceptible to degradation caused by water due to its hydrophilic nature and porous structure. Therefore, developing sustainable strategies to protect wood is of significant importance. This study aims to produce a highly hydrophobic coating for the protection of wood following a straightforward procedure and using materials that are compatible with wood. First, nano/sub-microlignin (NL) is isolated and produced from beech wood through a one-step tailored organosolv process. Next, NL is incorporated into Sivo 121, a water-borne and solvent-free silane system recommended by the manufacturer for protecting wood surfaces. Composite coatings containing various concentrations of NL and Sivo 121 are applied to chestnut (Castanea spp.) and oak (Quercus spp.). The impact of NL concentration on the contact angles of water drops (CAs) and colour changes (ΔE) of the treated wood specimens is investigated. The coating with 4% w/w NL demonstrates enhanced hydrophobicity (CA = 145°) and has a negligible effect on the colour of pristine oak (ΔE < 3). The wetting properties of coated oak are not affected after 100 tape peeling cycles. However, the coating exhibits poorer performance on chestnut, i.e., CA = 135°, which declines after 80 peeling cycles, and ΔE > 5. The drop pH does not have any noticeable effect on CA. The latter remains stable even after prolonged exposure of coated oak and chestnut samples to artificial UV radiation and outdoor environmental conditions. Finally, the composite coating offers good and comparable protection for both wood species in the biological durability soil burial test

Wear phenomena on natural stone of the cultural heritage are induced from various sources. Consequently, the development of multifunctional protective materials which combine two or more useful properties is an effective strategy to address the synergistic effects of various wear mechanisms. A multifunctional coating, consisting of a silane-based precursor and zinc oxide (ZnO) nanoparticles (NPs), is produced and tested for the protection of limestone. The hybrid coating combines the following three properties: superhydrophobicity, including water-repellency, photocatalytic self-cleaning and biocidal activity. The relative concentration of the NPs (0.8% w/w), used for the suggested composite coating, is carefully selected according to wetting studies, colourimetric measurements and durability (tape peeling) tests. The non-wetting state is evidenced on the surface of the composite coating by the large contact angle of water drops (≈153°) and the small contact angle hysteresis (≈5°) which gives rise to the physical self-cleaning scenario (lotus effect). The photocatalytic chemical self-cleaning is shown with the removal of methylene blue, induced by the UV-A radiation. Moreover, it is shown that the suggested coating hinders the incubation of E. coli and S. aureus as the inhibition were 94.8 and 99.9 %, respectively. Finally, preliminary studies revealed the chemical stability of the suggested coating.

Superhydrophobic materials have clear potential for mitigating rain/humidity-induced damage to cultural heritage. In the present study, the wetting properties of Paraloid B72 were tailored to achieve superhydrophobicity by incorporating modified calcium carbonate (CaCO₃) nanoparticles (NPs). B72 is a well-established conservation product while CaCO₃ is chemically compatible with calcareous materials commonly found in cultural heritage buildings and objects. Initially, the wettabilities of CaCO₃ NPs, functionalised with caproic (C6), caprylic (C8), lauric (C12), myristic (C14), palmitic (C16), and stearic (C18) acid, were evaluated by measuring water contact angles (CAs) on NP pellets. For NPs with short hydrocarbon chains, CA increased with chain length, from 66.3° for CaCO₃-C6 to 118.0° for CaCO₃-C12 NPs. For NPs with longer chains, CA remained stable and around 118°. Based on these results, CaCO₃-C12 NPs were selected for further investigation and subjected to transmission electron microscopy analysis, which revealed chain-like agglomerates of aggregated nanocrystallites (5–10 nm) forming 40–150 nm polycrystalline NPs. Scanning transmission electron microscopy combined with elemental mapping revealed a homogeneous distribution of Ca, C, and O within the NPs. Next, CaCO₃-C12 NPs were dispersed in B72 solutions and sprayed onto limestone, which was employed as a model calcite-rich substrate. At optimal NP concentration, the resulting composite coating exhibited superhydrophobicity (CA > 150°), while it induced minimal colour alteration to limestone and effective resistance to capillary water absorption. The fluorine-free coating also demonstrated good durability against UV exposure, drop impact, salt attack, freeze–thaw cycles, tape peeling, drop pH variations, and thermal treatment.