Silica Sol-gel Coatings with Improved Light Transmittance and Stability

Silica sol-gel coatings on different substrate materials and their use as model systems have been studied. Mesoporous silica coatings with thicknesses of 85 - 135 nm and porosity of 18 ˗ 37% were prepared by dip-coating on polycarbonate and glass substrates. In order to eliminate the shrinkage of the porous structure acid or base vapour treatment was applied. Thickness and refractive index of the coatings were determined by analysing the transmittance spectra of the samples. Ellipsometric porosimetry measurements were carried out to determine the porosity, pore radius distribution, thickness and refractive index. The thickness of the samples was further confirmed by scanning electron microscopy. The adsorption capacity of the porous coatings was also studied by dye impregnation tests. The temporal stability of the samples was investigated by UV-Vis spectrometry and it was found that the advantageous optical properties (Tmax = 98 – 99%) of the samples remained constant even after a 1 year storage period

Introducing nanoscaled surface morphology and percolation barrier network into mesoporous silica coatings

Mesoporous silica thin films were patterned at the sub-micron scale utilizing the ion hammering effect in order to combine the advantages of mesoporous character and surface morphology, while preserving the interconnected pore system or creating laterally separated porous volumes surrounded by nonpermeable compact zones. Porous silica coatings were prepared by a sol-gel method with an ordered and disordered pore system using micellar templates. A hexagonally ordered Langmuir-Blodgett type monolayer of silica spheres was applied as a mask against Xe+ ion irradiation. The ion energy was chosen according to Monte-Carlo simulations to achieve structures with high lateral contrast between irradiated and unirradiated, i.e., masked areas. The disordered pore system proved to be more resistant against ion bombardment. Although the created surface morphologies were similar, the main character of the pore system could be tailored to be interconnected or separated by controlling the ion fluence. Confocal fluorescence images and ellipsometric porosimetry measurements confirmed that the contribution of transition zone between the intact masked and damaged regions to the porosity is negligible. Furthermore, the majority of the porous volume can be preserved as an interconnected pore system by the application of low ion fluence. By increasing the fluence value, however, separated porous volumes can be created at the expense of the total pore volume