77 research outputs found
Gold Nanoparticles in Melting Gels
Melting gels were prepared by the solâgel process from methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES). Two compositions, 75 mol% MTES-25 mol% DMDES and 65 mol% MTESâ35 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 Gâ(t,Ï0) and loss Gâ (t,Ï0) 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. UVâVis 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 organicâinorganic consolidated melting-gel coatings for protection of 304 stainless steel in NaCl solutions
Homogeneous and crack-free methyl-substituted organicâinorganic hybrid glass coatings (thickness up to 10 ÎŒm) 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 cmâ2) 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.
Ironâiron oxide core-shell structured nanocomposites exhibited excellent humidity sensing behaviour.
Goldâgold 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, 1â
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 coreâsilver 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 coreâiron 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
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