Growth of AgCl cubic crystals at the surface of sol−gel silica films containing AgCl nanocrystals and poly(ethylene glycol)/ ethylene glycol as diffusion-controlled media has been successfully demonstrated. Crystals were grown during the shrinking of the film when it was exposed to air at room temperature, and both size and shape of the crystals were found to be dependent on the film thickness. When the film thickness was in the range of 70−250 nm, cubic shaped crystals with size between 120 and 250 nm were produced. These cubes exhibited predominant {200} facets as indicated by the electron beam diffraction patterns. Spherical crystals with size and height between 200 and 400 nm were observed when film thickness was in the range of 250−400 nm, while elliptical crystals were found on films thicker than 400 nm. Crystals were not grown when the film thickness was <25 nm. These results suggest that sol−gel silica films can be utilized as a nanocrystal reservoir to grow crystals of desired size and shape with their locations controlled by the pattern of the film.

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Materials synthesized via solution route sol-gel method are suitable for applications that rely on selectivity in diffusion, [1] size exclusion and filtration, [2] and encapsulation [3,4] because of their intrinsic nanoporous structures. These pore structures that occur spontaneously during the gelation reaction are highly interconnected. Many literatures have reported on how pore diameters, pore structures, and pore volumes can be controlled. [5,6] However, using these nanoscale pores as the template to produce secondary interconnected structures has been difficult due to that limited diffusion and the existing defects usually result in uneven distribution. We have reported that by incorporating low molecular weight polyethylene glycol (PEG), silver nanoparticles and silver chloride nanoparticles inside the pores of sol-gel materials remain mobile and they are able to transport to the surface when the sol-gel material is under shrinkage-induced stress. [7] It is known that silica materials synthesized by sol-gel method tend to shrink during drying. Solvent evaporation causes the pore structure of sol-gel materials to collapse and shrink, and such shrinkage often induce stress, resulting in cracks. This is particularly common on films made by sol-gel processes as cracks are often thickness-dependent. [8] Here we demonstrate that the microcracks also occur during the drying of a monolithic sol-gel sample and such microcrack surfaces can be utilized as the template to form interconnected silver structures (Scheme 1a). We also show that the density of silver structure is related to the volume shrinkage rate in the drying process while the density is not related to the final annealing stage where the induced stress and reductive polymer environment facilitate the formation of interconnected silver network without causing the sample to disintegrate (Scheme 1b).The general procedure for creating interconnected silver network in sol-gel nanocomposites includes preparation of wet gels, followed by aging and drying to form xerogels, and then annealing heat-treatment at 160 8C. The drying step was carried out by heat treatment at various temperatures (40-80 8C) to achieve various degrees of drying states prior to the final annealing step at 160 8C. During the annealing treatment, black samples became sliver reflective color, indicating metallic silver layers have been produced. We have previously reported that interconnected silver layers appear on both surface and internal space of sol-gel materials, and their interconnectivity is related to the amount of polymer in the samples. [7] Here, the sample dimension at each stage was shown in order to evaluate the degree of drying for the drying process (Figure 1). All aged gels retained 85% of the original size of wet gel volume and, respectively, shrank to 78, 72, and 61% of the wet gel size when drying for 4 h at 40, 60, and 80 8C. The final size after annealing is %55% of the wet gel and this value is independent of the drying process. Therefore COMMUNICATION [*] Dr.An inter...

A aminosilica nanocomposite layer containing a monolayer of gold nanoparticles (d = 18-22 nm) with a well-defined spacing was spontaneously deposited on an unmodified polystyrene surface via a sol-gel reaction when the reduction reaction was carried out under 1:8 molar ratio (gold(III):aminosilane). The amount of aminosilica and spacing between gold nanoparticles were found to be a function of the aminosilane:water molar ratio, which contributes to the plasmonic property of the films with its absorption wavelength ranging between 701 and 548 nm. Furthermore, the nanocomposite film that consists of a monolayer of nanoparticles in aminosilica has also been deposited on the surface of polystyrene beads. This core-shell structure was found capable of storing electrostatic charges and forming a well-separated 2D array.