Gold Nanoparticles in Melting Gels

Melting gels were prepared by the sol–gel process from methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES). Two compositions, 75 mol% MTES-25 mol% DMDES and 65 mol% MTES–35 mol% DMDES, were compared. Citrate-capped gold nanospheres were added to the melting gels during the synthesis process in five concentrations 8, 10, 12, 14, and 18 nM. The doped melting gels were studied both before and after their consolidation into hybrid glasses. Oscillatory rheometry and differential scanning calorimetry were employed to determine glass transition temperatures of the gels. According to oscillatory rheometry performed at constant frequency, the gels initially behave as viscous fluids and this continues as temperature is decreased, while recording the evolution of both storage G’(t,ω0) and loss G” (t,ω0) moduli with temperature. Glass transition temperature was determined as the moduli crossover point. Viscosity was dependent on temperature, but showed little variation with stress. As a general trend, viscosity decreased in the doped gels when compared to the undoped gel. UV–Vis spectra were collected to verify the presence of the gold nanospheres and to monitor their size. For the consolidated samples the position of the plasmon peak reflected the interaction between the gold nanospheres and the hybrid glass matrix.