The thesis project concerns the characterization of modified silica based coatings in a home-made climate chamber. By dip coating a state-of-art hydrophobic silica thin film on silicon is prepared, using tetraethylorthosilicate (TEOS), methyltriethoxysilane (MTES) and octyltriethoxysilane (OTES) as precursors, and a full characterization is performed, carrying out a wide range of tests at room and sub-zero temperatures. These include optical microscopy, contact angles (static and dynamic), ellipsometry, IR spectroscopy, surface energy, and, for the evaluation of the anti-icing properties of the coating, ice delay, nucleation sites, sliding angle, frosting. A hydrophobic coating is obtained, with an advancing contact angle 89.7° ± 1.0° and a hysteresis of 19.5°, with a thickness of 135.7±2 nm. The effect of parameters such as temperature, humidity, volume of water droplets on the surface properties is studied and it is tried to find a correlation between surface and anti-icing properties. A consistent improvement in properties compared to plain silicon is observed, with an average freezing time of water drops almost doubled, regardless of their size. Furthermore, a difference between the number of drops freezing on the coating compared to the reference is observed (14 vs 45 a 2 μL), a gap that narrows as the volume increases. This can be explained by the significant decrease in nucleation sites, which varies from the (1.11±0.02)∙10^9 sites/m^2 on the coating to the (1.39±0.05)∙10^10 sites/m^2 on silicon. The coating appears to perform better than other similar ones found in literature as regards the sliding angle, managing to slide even at -5°C at relatively small angles. A preservation of the ice-phobic properties even after 15 frost/defrost cycles is highlighted.
Il progetto di tesi riguarda la caratterizzazione di coatings a base di silice modificata in una camera climatica home-made. Tramite dip coating, si è preparato un sottile film idrofobico in silice modificata su silicio, partendo da tetraetilortosilicato (TEOS), metiltrietossisilano (MTES) e ottiltrietossisilano (OTES) come precursori, e si è eseguita una caratterizzazione completa, svolgendo un’ampia gamma di test e a temperatura ambiente e sottozero. Questi comprendono microscopia ottica, angoli di contatto (statico e dinamici), ellissometria, spettroscopia IR, energia superficiale, e, per la valutazione delle proprietà antighiaccio del rivestimento, ice delay, siti di nucleazione, angolo di scivolamento, frosting. Si è ottenuto un coating idrofobico con angolo di avanzamento pari a 89.7° ± 1.0° e isteresi di 19.5°, con spessore di 135.7±2 nm. Si è studiato l'effetto di parametri come temperatura, umidità, volume delle gocce d'acqua sulle proprietà superficiali e si è cercato di trovare una correlazione tra superficie e proprietà antighiaccio. Si è osservato un miglioramento consistente delle proprietà rispetto al semplice silicio, con un tempo di congelamento medio delle gocce d’acqua quasi raddoppiato, indipendentemente dalla dimensione delle stesse. Si osserva, inoltre, una differenza tra il numero di gocce che ghiacciano sul rivestimento rispetto al riferimento (14 vs 45 a 2 μL), divario che si assottiglia all’aumentare del volume. Ciò può essere spiegato dalla diminuzione rilevante dei siti di nucleazione, che varia dai (1.11±0.02)∙10^9 siti/m^2 sul coating ai (1.39±0.05)∙10^10 siti/m^2 su silicio. Il rivestimento risulta essere maggiormente performante rispetto ad altri simili presenti in letteratura per quanto riguarda l’angolo di scivolamento, riuscendo a scorrere anche a -5°C ad angoli relativamente piccoli. Si sottolinea una conservazione delle proprietà ghiacciofobiche anche in seguito a 15 cicli di ghiacciamento-sghiacciamento.
Valutazione delle proprietà antighiaccio di ricoprimenti a base di silice modificata
ROSSON, GIACOMO
2023/2024
Abstract
The thesis project concerns the characterization of modified silica based coatings in a home-made climate chamber. By dip coating a state-of-art hydrophobic silica thin film on silicon is prepared, using tetraethylorthosilicate (TEOS), methyltriethoxysilane (MTES) and octyltriethoxysilane (OTES) as precursors, and a full characterization is performed, carrying out a wide range of tests at room and sub-zero temperatures. These include optical microscopy, contact angles (static and dynamic), ellipsometry, IR spectroscopy, surface energy, and, for the evaluation of the anti-icing properties of the coating, ice delay, nucleation sites, sliding angle, frosting. A hydrophobic coating is obtained, with an advancing contact angle 89.7° ± 1.0° and a hysteresis of 19.5°, with a thickness of 135.7±2 nm. The effect of parameters such as temperature, humidity, volume of water droplets on the surface properties is studied and it is tried to find a correlation between surface and anti-icing properties. A consistent improvement in properties compared to plain silicon is observed, with an average freezing time of water drops almost doubled, regardless of their size. Furthermore, a difference between the number of drops freezing on the coating compared to the reference is observed (14 vs 45 a 2 μL), a gap that narrows as the volume increases. This can be explained by the significant decrease in nucleation sites, which varies from the (1.11±0.02)∙10^9 sites/m^2 on the coating to the (1.39±0.05)∙10^10 sites/m^2 on silicon. The coating appears to perform better than other similar ones found in literature as regards the sliding angle, managing to slide even at -5°C at relatively small angles. A preservation of the ice-phobic properties even after 15 frost/defrost cycles is highlighted.File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.12608/67304