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

Thickness-properties synergy in organic–inorganic consolidated melting-gel coatings for protection of 304 stainless steel in NaCl solutions

Homogeneous and crack-free methyl-substituted organic–inorganic hybrid glass coatings (thickness up to 10 μm) were deposited on AISI 304 stainless steel. Different hybrid glasses obtained fromconsolidation of the diluted melting gels with various methyltriethoxysilane (MTES)/dimethyldiethoxysilane (DMDES) ratios were evaluated considering chemical structure, coating adhesion and corrosion protection. The 70MTES/30DMDES (molar%) melting-gel coating provided improved corrosion protection for this steel due to the synergy of different properties: a highly cross-linked inorganic structure, a coating plasticity based on the hybrid network, and a good adhesion to the substrate through hydroxyl groups. Electrochemical results showa good barrier film with a passive range of 500 mV, a lowanodic current density (0.03 nA cm−2) and impedance values of 109.5Ωcm2 after two months of immersion in 3.5 wt.% NaCl solution

Synthesis of Nanocomposites Using Glasses and Mica as Templates

Various nanocomposites were synthesized using either a silica-based glass or mica crystallites as the medium. In some cases by an oxidation or a sulfidation treatment a core-shell nanostructure could be generated. Iron–iron oxide core-shell structured nanocomposites exhibited excellent humidity sensing behaviour. Gold–gold sulfide core-shell nanorods exhibited a number of optical absorption peaks which arose because of their structural characteristics. Nanoparticles of silver and silver oxide could be aligned in a polymethylmethacrylate film by an a.c. electric field of 1 MHz frequency. The composites showed large sensitivity to relative humidity. Lead sulfide nanowires of diameter, 1⋅2 nm, were grown within the nanochannels of Na-4 mica. These exhibited a semiconductor to metal transition at around 300 K. This arose because of high pressure generated on the nanowires. Copper sulfide nanowires grown within the Na-4 mica channels showed metallic behaviour. Silver core–silver orthosilicate shell nanostructures developed within a silicate glass medium showed discontinuous changes in resistivity at some specific temperatures. This was explained as arising due to excitation of Lamb modes at certain pressures generated because of thermal expansion mismatch of the core and the shell phases. Optical properties of iron core–iron oxide shell nanocomposites when analysed by effective medium theory led to the result of a metal non-metal transition for particle diameters below a critical value. Similar results were obtained from optical absorption data of silver nanoparticles grown in a tetrapeptide solution