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Yang, Ning; Liu, Jia-Hui; Kai, Ming-Feng; Dai, Jian-Guo
Construction & building materials, 05/2024, Letnik: 428Journal Article
The longevity of geopolymer-based radiative cooling coatings is questionable due to their hydrophilic nature. This study used four hydrophobic agents - sodium methyl silicate (SMS), polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE), and triethoxyoctylsilane (TEOS) - to modify the surface hydrophobicity of geopolymer while maintaining its optical properties. The optimal agent contents were determined by optical performance and water contact angle: 5 % for SMS, 10 % for 50 cP viscosity PDMS, and a single-layer thickness for PTFE and TEOS (60 °C). The agents' working mechanisms were analyzed using FTIR and XRD characterization: SMS forms a hydrophobic alkylsilanol layer by reacting with the geopolymer's silanol group; PDMS lowers the geopolymer's surface energy with its hydrophobic methyl groups; PTFE's low electric polarizability is due to its fluorine content; and TEOS replaces the geopolymer surface's hydroxyl groups with hydrophobic octyl groups. The long-term durability of these modified coatings was evaluated through outdoor exposure tests, resulting in total solar reflectance losses of 0.74 %, 1.9 %, 3.9 %, and 0.05 % respectively. A slight reduction in the water contact angle confirmed their enduring hydrophobic characteristics. These modification methods open up possibilities for the practical use of hydrophobic geopolymer radiative cooling coatings. •SMS, PDMS, PTFE and TEOS could tailor geopolymer’s hydrophobic properties.•If designed well, the effect of modifiers on the optical properties was ignorable.•SMS and TEOS reacted with geopolymer, but PDMS and PTFE did not.•Outdoor exposure revealed a limited reduction in optical and hydrophobic properties.•SMS, PTFE and TEOS were beneficial for the bond strength, but PDMS was not.
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Leto | Faktor vpliva | Izdaja | Kategorija | Razvrstitev | ||||
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JCR | SNIP | JCR | SNIP | JCR | SNIP | JCR | SNIP |
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in: SICRIS
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