Organo-mineral textured coatings with enhanced water repellency
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Дата
2025
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Igor Sikorsky Kyiv Polytechnic Institute
Анотація
Li Che. Organo-mineral textured coatings with enhanced water repellency. - Qualified scientific work on the rights of the manuscript. Dissertation for the degree of Doctor of Philosophy in the specialty 161 - Chemical Technologies and Engineering and Knowledge branch 16 – Chemical Engineering and bioengineering - National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute", Kyiv, 2025.
This study is aimed at establishing the possibility of using scalable organomineral surfaces to achieve tunable water wettability. To this end, systems comprising a mineral filler with particles of controlled shape and a polymer binder, as well as a thin organic layer with an extractive texture on the surface, are considered. The study demonstrates the relationship between the size, shape, and hierarchy of the textureforming elements and the surfaces' water-repellent properties, as well as their durability under ultraviolet radiation exposure. This study also contributes to addressing the major challenge of scaling up superhydrophobic surfaces. Since the systems investigated here are based on polymer binders combined with dispersed mineral fillers, this approach can be readily scaled to produce such coatings over large areas using existing manufacturing technologies. The purpose of this study is to establish the connection between the structure and water repellency of organo-mineral surfaces. The object of research is textured surfaces with tuned water repellency on the base of organic interface layer and mineral texture forming elements. The subject of research is the formation of water repellency of textures consisting of mineral structure formers and organic binding and interface layers. It has been shown that in organo-mineral systems based on dispersed particles - using red mud as an example - the water-repellent properties are governed by a combination of key factors: the ability of the particles to form a textured coatingsurface, which in turn depends on the ratio between the particles and the polymer matrix; the surface inertness of the filler particles, with higher inertness leading to more stable water-repellent surfaces; and the particle size, as smaller particles contribute to higher contact angles and thus improved water-repellent performance. Using an integrated approach based on hydrothermal synthesis, Zn-O-based particles with tunable morphology were obtained. By adjusting parameters such as temperature, catalyst type, reaction medium acidity, and the presence of doping agents (e.g., titanium dioxide and silicon dioxide), it is possible to control the particle size within a range of several tens to hundreds of nanometers, introduce hierarchical surface structures, and tailor the shape of the primary crystals, including plate-like, elongated, or irregular particles with complex architectures. It has been shown that the use of hierarchical zinc oxide-based particles, particularly those doped with titanium dioxide, leads to a significant enhancement in water-repellent performance compared to undoped or structurally simple particles. The observed increase in contact angle is approximately 20°, enabling the creation of truly superhydrophobic surfaces based on these hierarchical structures. It has also been demonstrated that superhydrophobic surfaces can be achieved over a broader range of nanoparticle concentrations (20-60 wt. %) when the particles possess a hierarchical surface structure. Unlike those lacking a distinct dual-level hierarchy, such particles enable stable water repellency even as the filler concentration varies. The studied materials with high specific surface area have shown strong potential for use in atmospheric water harvesting from fog. It was found that hydrophobic surfaces enable condensation of up to 7 grams of water per minute. In contrast, hydrophilic surfaces—achieved either by using unmodified mineral particles or by annealing—can collect up to 8.5 grams of atmospheric moisture per minute. The scientific novelty of the study is as follows: For the first time, it has been demonstrated - using red mud as an example - that surface inactivation of its particles, achieved by reducing their polarity through thermal treatment at 950 °C and modification with organosilicon compounds, enables the effective use of such waste as texture-forming components in the production of coatings with pronounced waterrepellent properties. In particular, contact angles of approximately 143° were achieved on the treated surfaces. This study advances the theoretical understanding of the formation of waterrepellent surfaces composed of dispersed micro- and nanoparticles embedded in organic polymer matrices. It was shown that particle surface topography and their chemical inertness play a critical role in generating effective surface texture. Additionally, fine-tuning the ratio between the polymer and the film-forming agent allows precise control over the coating structure, enabling the achievement of maximum contact angles. In this work, contact angles as high as 154° were obtained. This study further develops the understanding of the synthesis of zinc oxide (ZnO)- based particles with tunable morphology. It has been demonstrated that the particle shape is governed by a combination of factors, including the type of catalyst used, the synthesis temperature, the presence of dopants such as TiO₂ and SiO₂, and the ZnO-todopant ratio. By adjusting these parameters, it is possible to control the particle morphology, ranging from plate-like structures typical of pure ZnO to complex hierarchical architectures characteristic of doped forms. It has been shown that doped forms of zinc oxide (ZnO) crystals exhibit pronounced photoactivity. This effect is significantly enhanced when titanium dioxide (TiO₂) is used as a dopant. Specifically, photoluminescence analysis revealed that at a ZnO:TiO₂ ratio of 2:1, the photoactivity increases by approximately 6.5 times compared to undoped ZnO. For the first time, it has been demonstrated that the use of titanium-dioxide-doped zinc oxide particles with a highly developed surface structure leads to a significant enhancement in water-repellent properties compared to conventional nanoscale ZnO particles. At high filler loadings, the contact angle increases from 135° to 154°, classifying such coatings as superhydrophobic. It has been demonstrated for the first time that the developed hierarchical micro/nanostructure of doped zinc oxide particles enables the formation of highly water-repellent surfaces across a broad range of mass ratios between the polymer matrix and the mineral texture-forming particles. Specifically, when the content of doped ZnO/CO₂ particles ranges from 20% to 60%, contact angles remain above 140°. In contrast, the use of individual TiO₂, CO₂, or ZnO particles results in such high waterrepellent performance only within much narrower concentration ranges. It has been shown that coatings containing texturing elements based on modified ZnO particles doped with TiO₂ and SiO₂ exhibit high resistance to UV-induced hydrophilization. These coatings transition from the Cassie–Baxter state to the Wenzel state only after 170 hours of UV exposure, while maintaining a contact angle of approximately 120°. Complete hydrophilization occurs only after 250–280 hours of continuous irradiation. It has been shown that textured surfaces, particularly those with hierarchical micro/nanostructures, are effective for fog water collection. The efficiency of water harvesting significantly increases upon hydrophilization of the surface, with an observed improvement of approximately 30–45% compared to hydrophobic surfaces. The practical significance of the obtained results is as follows: In the course of this work, a novel synthesis method was developed for doped hierarchical ZnO–SiO₂ and ZnO–TiO₂ particles. These materials can serve as a basis for water-repellent textured coatings and are also considered promising hydrophilic materials for atmospheric moisture harvesting. Additionally, both types of particles exhibit pronounced photoactive properties, expanding their potential for use in multifunctional surface applications. The developed organo-mineral coating formulations based on composite hierarchical ZnO particles doped with titanium dioxide and silicon dioxide exhibit stability under ultraviolet irradiation for over 170 hours. These coatings retain their hydrophobic properties under prolonged UV exposure, making them promising candidates for use as UV-resistant water-repellent surfaces.
Опис
Ключові слова
red mud, nanoparticles, composite, titanium dioxide, polymer, silica, modification, styrene acrylate, hydrothermal treatment, zinc oxide, червоний шлам, наночастинки, композит, діоксид титану, полімер, діоксид кремнію, модифікування, стирол-акрилат, гідротермальна обробка, оксид цинку
Бібліографічний опис
Li Che. Organo-mineral textured coatings with enhanced water repellency : dissertation submitted for the Doctor of Philosophy degree : 161 Chemical Technologies and Engineering / Li Che. – Kyiv, 2025. – 165 p.