Abstract
Condensed water either as a rainfall or as humidity, is one of the main factors for outdoor materials deterioration and decay, including stone and stone based monuments’. Nowadays, the protection of outdoor materials from natural weathering is pursued by the application of water-repellent polymer films. At the first section of the present thesis the performance of synthetic coatings used for the protection of monuments of Hellenistic and Byzantine period is evaluated. The obtained results demonstrated that it is enhancement of the hydrophobicity of the coatings is required, especially on low porosity materials, like e.g. marbles. The surface hydrophobicity can be enhanced by altering (increasing) it’s surface roughness. In this framework a new strategy resulting in a significant enhancement of the hydrophobicity of the polymers is developed. The methodology, which is simple and low cost, is summarized as follows: nanoparticles are dispersed in a polymer solution. The mixture is then sp ...
Condensed water either as a rainfall or as humidity, is one of the main factors for outdoor materials deterioration and decay, including stone and stone based monuments’. Nowadays, the protection of outdoor materials from natural weathering is pursued by the application of water-repellent polymer films. At the first section of the present thesis the performance of synthetic coatings used for the protection of monuments of Hellenistic and Byzantine period is evaluated. The obtained results demonstrated that it is enhancement of the hydrophobicity of the coatings is required, especially on low porosity materials, like e.g. marbles. The surface hydrophobicity can be enhanced by altering (increasing) it’s surface roughness. In this framework a new strategy resulting in a significant enhancement of the hydrophobicity of the polymers is developed. The methodology, which is simple and low cost, is summarized as follows: nanoparticles are dispersed in a polymer solution. The mixture is then sprayed on the substrate and the resulting composite polymer-nanoparticle film exhibits superhydrophobic properties. Hydrophilic silica (SiO2) nanoparticles were dispersed in solutions of poly(methyl methacrylate) (PMMA) and in solutions of a commercial poly(alkyl siloxane) and the suspensions were sprayed on glass surfaces. The morphology of the polymer-particle composite films was studied showing that a two-length-scale hierarchical structure is formed on the surface. The developed surface morphology resembles to a large extent to morphology of the surface of the Lotus leaf, which is known for its super-hydrophobic properties. The hydrophobicity of the composite films as a function of the nanoparticle concentration was also examined showing that the treated surfaces became super-hydrophobic. Consequently the water droplets could roll-off and thus assuring maximum protection against water. The obtained results were discussed in the light of Wenzel and Cassie-Baxter theoretical models. Super-hydrophobicity was also developed on various substrates and water contact angle measurements demonstrated that the substrate has almost no effect on the hydrophobic character of the applied coatings, which were produced on silicon, concrete, aluminum, silk, wood and marble. viii Furthermore the addition of various particles in the hydrophobicity of the composite films was studied. In particular a poly(alkyl siloxane) was mixed with SiO2, SnO2, Al2O3 and ZnO nanoparticles with particle size 7-70 nm resulting in the formation of composite films with super-hydrophobic properties. The water contact angle measurements as a function of the nanoparticle concentration showed that the maximum hydrophobicity is independent of the nanoparticle and is determined by the Young’s contact angle of the pure polymer and that the concentration of nanoparticles in a super-hydrophobic composite film is determined by the specific surface area and the mean size of the nanoparticles. The protective efficacy of the polymer-particle composite films was evaluated on white Greek marbles and on porous stones used for the restoration of the Castle of Prague, Czech. In the event that hydrophobicity is not the sole parameter of optimal stone and stone-monuments protection, other important parameters, such as water vapor permeability, water capillary absorption and stone color alterations, were also investigated and their dependence on nanoparticle concentration was established. Finally for the evaluation of the robustness of the composite films, the treated substrates were tested against UV radiation and also were exposed to outdoor conditions.
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