M. Alejandra Mazo

Surface properties of bioactive TEOS–PDMS–TiO2–CaO ormosils

Tetraethyl orthosilicate (TEOS)–polydimethyl siloxane (PDMS) ormosils with different amounts of Ti and Ca were prepared and characterized. Several surface properties such as specific surface area, porosity, fractality, dispersive and polar surface energies were determined and related with their in-vitro bioactivity. It has been found a dependence of the surface fractal dimension with the concentration of Ca2+ ions that induce the appearance of rough surfaces. The dispersive surface energy, γSd, increased with the incorporation of Ti or Ca and the presence of micropores, but Ca(NO3)2 precipitates in the surface coming from non-incorporated Ca lead to a decrease of the surface energy values. In relation with the polar surface energy, it has been observed that all ormosil materials presented amphoteric character with a larger presence of base surface sites than acid ones. The basicity of the surface increased with the concentration of Ti and Ca, while the acidity decreased. The in-vitro bioactivity of the surface was estimated by soaking samples in simulated body fluid (SBF) and afterwards characterized by means of X-ray diffraction (TF-XRD) and field emission scanning electron microscopy (FE-SEM). It has been observed that in vitro bioactivity is related with the polar surface characteristics of these materials, being necessary for the bioactivity, the presence of a highly polar surface with intermediate base/acid ratio and specific roughness.

Stable highly porous silicon oxycarbide glasses from pre-ceramic hybrids

The introduction of Si–H bonds into the structure of a sol–gel derived ceramic material leads to a hybrid that generates a highly porous silicon oxycarbide material stable up to pyrolysis temperatures above 1200 °C. The fractal analysis reveals an increase in the pore anisotropy in the first stages of ceramisation of the pre-ceramic hybrid material indicating the creation of a narrow interconnected porous (<4 nm) network stable with temperature. The formation of C-enriched units during pyrolysis supports the porous structure throughout the thermal treatment strengthening against collapse. The presence of highly reactive bonds gives rise to huge differences in the pre-ceramic hybrid which radically influence the characteristics of the derived silicon oxycarbide materials. The hybrid material without Si–H bonds displays an open macroporous microstructure and during the thermal treatment the gaseous species generated inside can easily escape generating micropores, which tend to disappear as the temperature increases. However the presence of highly reactive Si–H bonds produces a fully dense material and during pyrolysis the different paths followed by the redistribution reactions favour the creation of a micro–mesoporous structure which is preserved up to 1200 °C.