Adhesion and degradation of hard transparent coatings
- Hard transparent coatings are an essential component of structures involving polymer surfaces. An important application is airplane passenger windows, which are subject to large variations in pressure, temperature and humidity as well as UV exposure and abrasive conditions. The coatings suitable for such extreme environments must have high hardness, resistance to UV degradation and excellent adhesion to the polymer substrate. Measuring the adhesion of a hard coating on a compliant substrate is not trivial; hence, qualitative cross-cut tape tests have been the standard for automotive and aerospace industries. In this dissertation we address the quantitative assessment of adhesion of hard transparent coatings on polymer substrates. An asymmetric double cantilever beam specimen was employed to sample the interface without contribution from crazing in the substrate. Fracture energies of coatings that had passed standard tests were found to vary from 1.4 J/m2 to 22 J/m2. Significant subcritical crack growth was observed in coatings on windows with interfacial fracture energy of 7 J/m2. Cracks were found to continue to grow at driving forces below 2 J/m2 due to viscoelastic deformation at the crack tip. Simulated outdoor weathering decreased the adhesion energy and led to cracking and delamination. Driving force for cracking and delamination was correlated to UV cross-linking of the coating; FTIR evidence showed that the ratio of network forming Si—O—Si bonds increased with outdoor exposure. The effect of surface pre-treatments on adhesion was assessed. Mechanical polishing and UV-Ozone treatment were found to increase adhesion significantly. The effect of UV absorbers on stress generation in coatings exposed to UV was investigated. A cyanoacrylate absorber was found to perform better than a benzophenone absorber at high concentrations. However, both absorbers seemed to change the molecular structure of the coating and did not increase the lifetime of the coating significantly. Atmospheric plasma deposition was employed as a solvent-free and wasteless alternative to sol-gel processing of hybrid coatings. We focused on molecularly bridged hybrid coatings for improved cohesion and resistance to water assisted crack growth. A high temperature precursor delivery system was designed and constructed for deposition of molecularly bridged hybrid silica coatings. Bridged precursors with very low vapor pressure were deposited on silicon and polycarbonate substrates. The effects of precursor flow rate, temperature and other plasma parameters on deposition rate were investigated. Bridged precursor coatings developed significantly higher growth stresses than curing stresses in sol-gel coatings, but the former were comparable to atmospheric plasma coatings deposited using conventional silanes.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Stanford University, Department of Materials Science and Engineering
|Lindenberg, Aaron Michael
|Lindenberg, Aaron Michael
|Statement of responsibility
|Submitted to the Department of Materials Science and Engineering.
|Thesis (Ph.D.)--Stanford University, 2010.
- © 2010 by Anay Yazlali
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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