Ultrathin carbon layers, on the order of 3-6 nm in thickness, were formed on glass substrates by spin coating and pyrolysis of polymer precursors. The organic precursors used were poly(furfuryl alcohol), coal tar pitch, and a photoresist. The carbon coatings were characterized by ellipsometry, optical profilometry, water contact angle, confocal Raman spectroscopy, UV-vis spectroscopy, and atomic force microscopy. We also report the transparency, hydrophobicity, friction, weathering resistance, and electrical conductivity of the carbon-coated glass. The results reveal that up to 97% transparent, ultrathin carbon films could be formed on glass substrates with a root-mean-square roughness of less than approximately 0.3 nm. This carbon layer modified the otherwise hydrophilic surface of the glass to yield a water contact angle of 85 degrees . The coatings were also found to provide a water barrier against weathering under hot and humid conditions. A 4.5-nm-thick carbon film on glass had a sheet resistance of 55.6 kOmega m and a conductivity of 40 S/cm.
The dielectric breakdown behavior of alkali‐free glass was determined as a function of thickness and surface roughness. The thickness of commercially available glass (as‐received thickness=50 μm) was reduced to a range of thicknesses between 47 and 5 μm by chemical etching. The RMS surface roughness of the as‐received glass was in the range of 0.14–0.47 nm, and the surface roughness increased to up 10 nm after etching; it was also found that agitating the etching solution by ultrasound reduced the overall surface roughness. The evaluation of these samples revealed that the dielectric breakdown strength increased as the thickness decreased. However, the Weibull modulus representing the distribution of dielectric strengths showed a dependence on the surface roughness of the etched glass. A power law dependence, EB∝d−n, where d is the glass thickness and n=0.14 and 0.86, has been found to fit the data in the respective thickness ranges of 5–20 and 25–50 μm. Self‐healing behavior, which allows the dielectric to continue to support a high electric field after breakdown, was found to be more likely as the dielectric layer thickness decreased. The susceptibility to self healing was correlated with the stored electrostatic energy and latent heat of vaporization for the gold electrode material.
Spin-coated waterborne polyurethane to protect glass surface from environmental attacks was cured by using microwave heating. The effect of microwave heating on the reaction kinetics, chemical durability, and transmittance of polyurethane was investigated. In comparison to the conventional heating the results show that the microwave heating substantially accelerates the curing process of waterborne polyurethane and the total time for the completion of the reaction is only 1/7 of that in the conventional process. The microwave cured sample showed an excellent caustic resistance compared to conventional cured one. It means that microwave heating produces dense structure during curing process. The dense structure does not affect to the transmittance in the visible region.
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