Esmaspäeval, 4 detsembril 2017 kell 14.15 toimub Physicumis, W.Ostwaldi 1, seminariruumis D312
Nanostruktuuride ja Laserspektroskoopia laborite
ÜHISSEMINAR No 249
Triin Kangur, post-graduate, Laboratory of Physics of Nanostructures, Institute of Physics, University of Tartu, Ostwaldi st 1, Tartu, Estonia
Preparation and functional properties of stochastic microstructured sol-gel silica materials (materials of PhD thesis)
Mikrostruktuursete ränioksiidsete sool-geel materjalide arendamine ja funktsionaalsete omaduste hindamine (doktoritöö materjalid)
In the thesis two types of microstructured silica coatings are introduced. Our aim was to explore two distinct preparation methods for obtaining silica domes and a silica foams with sphere-like morphology, and to characterize and evaluate the applicability of these structured materials.
Material formation is based on concurrent phase separation and sol–gel transition processes. In both preparation processes, the increase in precursor solution viscosity is the key to structure formation and the final structure is determined by the freezing point of sol-gel transition. In the case of surface coating with domes, the structuring was formed through a continuous separation of the silica-rich phase from the sol. The foam film coating was prepared with the help of purposely created hydrogen peroxide gas phase into the sol.
It was demonstrated that by choosing suitable alkoxide concentration, solvent type, water- and catalyst-alkoxide molar ratios, it is possible to vary the size, shape and surface density of the domes. Sufficiently dense packing of silica domes in sub-µm range and multilayered coating were leading to a notable antireflection and light scattering effects in the Vis-NIR spectral range. As some produced silica surfaces had water contact angles exceeding 130°, simultaneous superhydrophobicity (contact angle > 150°) can be achieved by further surface functionalization (e.g. with fluoropolymer). These surfaces are also found to be biocompatible and it is shown that growth characteristics morphology of fibroblasts is influenced by the morphology of the substrate.
Sol-gel process together with catalytic decomposition of hydrogen peroxide is a novel method for the preparation of thick silica foam film, where well-defined closed-cell porosity appears. Macroporous characteristics and the lowest measured thermal conductivity (0.018 W/(m∙K)) of the prepared foams were similar to silica aerogels. These silica foam materials are potentially applicable as efficient thermal insulation materials.