Optically transparent and environmentally durable superhydrophobic coating based on functionalized SiO₂nanoparticles

Abstract

Optical surfaces such as mirrors and windows that are exposed to outdoor environmental conditions are susceptible to dust buildup and water condensation. The application of transparent superhydrophobic coatings on optical surfaces can improve outdoor performance via a 'self-cleaning' effect similar to the Lotus effect. The contact angle (CA) of water droplets on a typical hydrophobic flat surface varies from 100° to 120°. Adding roughness or microtexture to a hydrophobic surface leads to an enhancement of hydrophobicity and the CA can be increased to a value in the range of 160°-175°. This result is remarkable because such behavior cannot be explained using surface chemistry alone. When surface features are on the order of 100 nm or smaller, they exhibit superhydrophobic behavior and maintain their optical transparency. In this work we discuss our results on transparent superhydrophobic coatings that can be applied across large surface areas. We have used functionalized silica nanoparticles to coat various optical elements and have measured the CA and optical transmission between 190 and 1100 nm on these elements. The functionalized silica nanoparticles were dissolved in a solution of the solvents, while the binder used was a polyurethane clearcoat. This solution was spin-coated onto a variety of test glass substrates, and following a curing period of about 30 min, these coatings exhibited superhydrophobic behavior with a static CA ≥ 160°.

On the Durability and Wear Resistance of Transparent Superhydrophobic Coatings

“…Once transparency is also introduced into the equation, resistance to durability becomes more problematic since transparent surface texture roughness should not enhance Mie and Rayleigh scattering [18]. Mie scattering occurs when the diameter of the surface features are close to the wavelength of the incident photon, and Rayleigh scattering occurs when the size of the surface features are much smaller than the wavelength of the incident photon.…”

Abrasion Resistance of Superhydrophobic Coatings on Aluminum Using PDMS/SiO2

“…These functionalities include self-cleaning [1], anti-icing [2], anti-corrosion [3], and anti-biofouling [4] in addition to the native features of aluminum metal such as lightweight and commendable ductility. A wide variety of fabrication techniques are available for the creation of such coatings, which includes but is not limited to the template method [5], chemical etching [6], electro-spinning [7], chemical vapor deposition [8], self-assembled monolayers [9], and nanocomposites [10][11][12]. The two governing factors for developing a superhydrophobic coating are its surface chemistry (low surface free energy) and surface morphology (nano/microscale roughness) [13][14][15].…”

Multilevel Nanoparticles Coatings with Excellent Liquid Repellency

“…Recently, the superhydrophobic surfaces have been paid much attention, which are developed considerably, for example, self‐cleaning surfaces, anti‐icing surfaces, antibacterial surfaces, antifouling surfaces, or water–oil separation . Superhydrophobic coatings are considered to have more potential future, which have made great progress in recent years . For example, Lu et al reported the feasible preparation of a superhydrophobic coating with the “paint‐spray adhesive” combination structure, which enabled both hard and soft substrates to become superhydrophobic and self‐cleaning.…”