Postsynthetic processing of copper hydroxide-silica tubes.

Using reaction conditions far from equilibrium, we produce hollow tubes of silica-supported Cu(OH)2. The samples are then processed postsynthetically without compromising the macroscopic tubular structure. We specifically induce an amorphous-crystalline transition and demonstrate the sequential conversion of Cu(OH)2 to CuO, Cu2O, and metallic copper using thermal treatment and wet chemistry.

Tubular precipitation structures: materials synthesis under non-equilibrium conditions.

Inorganic precipitation reactions are known to self-organize a variety of macroscopic structures, including hollow tubes. We discuss recent advances in this field with an emphasis on experiments similar to 'silica gardens'. These reactions involve metal salts and sodium silicate solution. Reactions triggered from reagent-loaded microbeads can produce tubes with inner radii of down to 3 µm. Distinct wall morphologies are reported. For pump-driven injection, three qualitatively different growth regimes exist. In one of these regimes, tubes assemble around a buoyant jet of reactant solution, which allows the quantitative prediction of the tube radius. Additional topics include relaxation oscillations and the templating of tube growth with pinned gas bubble and mechanical devices. The tube materials and their nano-to-micro architectures are discussed for the cases of silica/Cu(OH)(2) and silica/Zn(OH)(2)/ZnO tubes. The latter case shows photocatalytic activity and photoluminescence.

Controlling the wall thickness and composition of hollow precipitation tubes.

We investigate the growth of self-organized tubes formed by injection of metal salt solutions into silicate solution. The wall thickness increases strictly in an inward direction and obeys square root functions suggesting the presence of a traveling reaction-diffusion front in the radial direction. We also demonstrate the construction of multi-layered tubes.

Micropatterned polyvinyl butyral membrane for acid-base diodes.

Until now, polyvinyl alcohol (PVA) gel cylinders have been used in electrolyte diodes as a connecting element between the acidic and alkaline reservoirs. In this paper, a new connecting element is reported: a breath figure templated polyvinyl butyral (PVB) membrane prepared with dip-coating from a dichloromethane solution of the polymer in a humid atmosphere. The procedure gives a 1.5-2 µm thick membrane with a hexagonal pattern, the average characteristic length of which is 1 µm. After an acidic etching, it was found to be a good connecting element. The voltage-current characteristics and dynamic properties of PVA and PVB were measured and compared. The PVB membrane has a faster response to voltage changes than the PVA gel, but in both cases, there was a slow drift in the current that prevented it from reaching a steady state. Reproducible characteristics can be obtained, however, after the current reaches a well-defined quasi-steady state.