Simple solutions to the fabrication of textured and porous coatings

Abstract

<p>Functional coatings can change the surface properties of the substrate, add entirely new surface functionalities, or preserve the substrate. They provide solutions to many key engineering problems where different functionalities between the surface and the bulk are required. Among them, textured coatings are characterized by their surface roughness, film porosity, and surface chemistry. They are useful for applications ranging from superhydrophobic surfaces to artificial implants to thermal barrier coatings. However, the use and deployment of new coating methods are hampered in real applications due to the lack of a comprehensive consideration of the associated issues. In this thesis, two deposition methods were studied to solve two critical problems in coating fabrication, respectively. Their preparation procedures were designed according to the criteria of simple solutions which are inexpensive, reliable, predictable, highly performing, “stackable” (i.e., they can be combined and compounded with little increase in complexity), and “hackable” (i.e., they can be easily modified and optimized). The first method is to solve the demanding problem of the outdoor use of superhydrophobic coatings that must satisfy multiple demands (scalability, adhesion to curved surfaces, thermal expansion compatibility, UV radiation, wear tolerance, etc.). Most of the methods reported in literature and commercial solutions do not meet all the requirements. Our solution is to use silicones (a common type polymer) and their thermal decomposition (a self-structuring process) by flames (a high throughput tool). The second method is to simplify the fabrication of nanocrystalline mesoporous thin film coatings with controlled porosity and surface chemistry, good mechanical properties for device integration. Mesoporous thin films built directly from nanocrystals are desirable for many applications, but the use of ligand-capped colloidal nanocrystals has been so far prevented by the presence of ligands, and the low porosity of the assembly. Our solution is to combine two concepts: (i) the increase of porosity in disordered assemblies of anisotropic building blocks with their aspect ratios, and (ii) the complete removal of ligands and the surface chemistry tuning provided by plasma processing. The performances and mechanisms of the two type of coatings were studied. The simplicity of the two solutions was then discussed.</p>