Preparation and optical characterization of catalyst free SiO2 sonogel hybrid materials

Abstract

The synthesis of sol-gel materials induced by ultrasonic irradiation (sonolysis) is implemented as an alternative method for the fabrication of highly pure organic-inorganic composites with good monolithic, mechanical and optical properties. Ultrasonic irradiation, instead of commonly used basic- or acidic-catalyst was used to produce acoustical cavitation within the liquid H2O/tetraethyl-ortosilicate (TEOS) reactants. This procedure forms a hydrolyzed-TEOS colloidal dispersion (sol) which produces, after drying, a highly pure SiO2 network. The resulting SiO2 glass exhibits high porosity and allows the inclusion of several organic compounds in the colloidal sol-state. Novel, optical active synthesized liquid crystalline (LC)-azo-compounds, bent shaped mesogens, cis- and trans-poly(1-ethynylpyrene)s, as well as fullerene (C60) spheres and classical organic dyes were successfully incorporated as dopant agents within the novel catalyst free (CF) SiO2-sonogel host matrix. Absorption and fluorescence spectroscopy studies were carried out in order to characterize the optical performance of both the CF-sonogel and several hybrid composites The pulsed laser photoacoustic technique (LPAT) was implemented to determine thermodynamic phase transitions of LC-based hybrids and laser induced damage (photo-degradation) in dye-based composites. Finally, comparative morphology studies between undoped reference samples and some doped composites were performed by Atomic Force Microscopy (AFM), where an optimal TEOS/dopant concentration ratio, to obtain good mechanical properties among the studied samples, has been found.