Superhydrophobic fluorinated oligomers as protective agents for outdoor stone artworks

Since ancient times, hydrophobic compounds have been used to protect natural stones exposed to environmental degradation agents. In this paper, we consider the properties of natural and synthetic compounds and discuss the performance of a synthetic water repellent, an oligosuberamide bearing perfluoropolyether segments (hereinafter FSB) as optimal protective agent for stone artefacts. FSB is soluble in alcoholic and hydro-alcoholic solvents, and it demonstrates high water inhibition efficacy on both low and highly porous stones, mainly due to its low surface tension (lower than that of natural compounds). Additionally, FSB preserves the original characteristics of stones, i.e. vapour diffusivity and chromatic features, showing good compatibility. FSB also manifests good environmental durability which permits outdoor application. The performance of FSB was comparatively studied with two homologous compounds, in terms of solubility and surface deposition characteristics. Exploiting SEM, a suitable roughness created by FSB agglomerates (1−100 μm) was observed, which accounts for its superhydrophobicity, along with its homogeneously distribution on both surface and in depth.