Synthesis of Inorganic Tubes under Actively Controlled Growth Velocities and Injection Rates

We describe an experiment that establishes control over the growth velocities of macroscopic tubes in the reaction between a polymerizable inorganic anion and a nonalkali metal ion. Our approach is demonstrated for the injection of an acidic cupric sulfate solution into a large volume of a basic sodium silicate solution. The forming tube is pinned to a gas bubble that is held at the end of a hollow glass rod. The tube’s linear growth follows the speed of the glass rod (0.5–11 mm/s), while its radius (0.2–1.6 mm) is self-selected according to the volume conservation of the injected solution. Depending on the experimental conditions, tube growth occurs at either the moving gas bubble or the stationary glass capillary. Oscillatory modulations of the growth velocity provoke the formation of hollow nodules on the outer tube surface. These nodules form after each rapid velocity decrease at exponentially decaying rates and seem to be energetically favored over a sudden isotropic increase in tube radius

Synthesis of Inorganic Tubes under Actively Controlled Growth Velocities and Injection Rates

We describe an experiment that establishes control over the growth velocities of macroscopic tubes in the reaction between a polymerizable inorganic anion and a nonalkali metal ion. Our approach is demonstrated for the injection of an acidic cupric sulfate solution into a large volume of a basic sodium silicate solution. The forming tube is pinned to a gas bubble that is held at the end of a hollow glass rod. The tube’s linear growth follows the speed of the glass rod (0.5–11 mm/s), while its radius (0.2–1.6 mm) is self-selected according to the volume conservation of the injected solution. Depending on the experimental conditions, tube growth occurs at either the moving gas bubble or the stationary glass capillary. Oscillatory modulations of the growth velocity provoke the formation of hollow nodules on the outer tube surface. These nodules form after each rapid velocity decrease at exponentially decaying rates and seem to be energetically favored over a sudden isotropic increase in tube radius

Nonequilibrium Synthesis of Silica-Supported Magnetite Tubes and Mechanical Control of Their Magnetic Properties

Materials synthesis far from thermodynamic equilibrium can yield hierarchical order that spans from molecular to macroscopic length scales. Here we report the nonequilibrium formation of millimeter-scale iron oxide–silica tubes in experiments that tightly control the tube radius and growth speed. The experiments involve the hydrodynamic injection of an iron (II,III) solution into a large volume of solution containing sodium silicate and ammonium hydroxide. The forming tubes are pinned to a motorized glass rod that moves at a predetermined speed. X-ray diffraction and electron microscopy, as well as Raman and Mössbauer spectroscopy, reveal magnetite nanoparticles in the range of 5–15 nm. Optical data suggest that the magnetite particles follow first-order nucleation–growth kinetics. The hollow tubes exhibit superparamagnetic behavior at room temperature, with a transition to a blocked state at <i>T</i>_B = 95 K for an applied field of 200 Oe. Heat capacity measurements yield evidence for the Verwey transition at 20 K. Finally, we show a remarkable dependence of the tubes’ magnetic properties on the speed of the pinning rod and the injection rate employed during synthesis

Synthesis of Inorganic Tubes under Actively Controlled Growth Velocities and Injection Rates

We describe an experiment that establishes control over the growth velocities of macroscopic tubes in the reaction between a polymerizable inorganic anion and a nonalkali metal ion. Our approach is demonstrated for the injection of an acidic cupric sulfate solution into a large volume of a basic sodium silicate solution. The forming tube is pinned to a gas bubble that is held at the end of a hollow glass rod. The tube’s linear growth follows the speed of the glass rod (0.5–11 mm/s), while its radius (0.2–1.6 mm) is self-selected according to the volume conservation of the injected solution. Depending on the experimental conditions, tube growth occurs at either the moving gas bubble or the stationary glass capillary. Oscillatory modulations of the growth velocity provoke the formation of hollow nodules on the outer tube surface. These nodules form after each rapid velocity decrease at exponentially decaying rates and seem to be energetically favored over a sudden isotropic increase in tube radius

Synthesis of Inorganic Tubes under Actively Controlled Growth Velocities and Injection Rates

We describe an experiment that establishes control over the growth velocities of macroscopic tubes in the reaction between a polymerizable inorganic anion and a nonalkali metal ion. Our approach is demonstrated for the injection of an acidic cupric sulfate solution into a large volume of a basic sodium silicate solution. The forming tube is pinned to a gas bubble that is held at the end of a hollow glass rod. The tube’s linear growth follows the speed of the glass rod (0.5–11 mm/s), while its radius (0.2–1.6 mm) is self-selected according to the volume conservation of the injected solution. Depending on the experimental conditions, tube growth occurs at either the moving gas bubble or the stationary glass capillary. Oscillatory modulations of the growth velocity provoke the formation of hollow nodules on the outer tube surface. These nodules form after each rapid velocity decrease at exponentially decaying rates and seem to be energetically favored over a sudden isotropic increase in tube radius

Nonequilibrium Synthesis of Silica-Supported Magnetite Tubes and Mechanical Control of Their Magnetic Properties

Materials synthesis far from thermodynamic equilibrium can yield hierarchical order that spans from molecular to macroscopic length scales. Here we report the nonequilibrium formation of millimeter-scale iron oxide–silica tubes in experiments that tightly control the tube radius and growth speed. The experiments involve the hydrodynamic injection of an iron (II,III) solution into a large volume of solution containing sodium silicate and ammonium hydroxide. The forming tubes are pinned to a motorized glass rod that moves at a predetermined speed. X-ray diffraction and electron microscopy, as well as Raman and Mössbauer spectroscopy, reveal magnetite nanoparticles in the range of 5–15 nm. Optical data suggest that the magnetite particles follow first-order nucleation–growth kinetics. The hollow tubes exhibit superparamagnetic behavior at room temperature, with a transition to a blocked state at <i>T</i>_B = 95 K for an applied field of 200 Oe. Heat capacity measurements yield evidence for the Verwey transition at 20 K. Finally, we show a remarkable dependence of the tubes’ magnetic properties on the speed of the pinning rod and the injection rate employed during synthesis

Self-Organized Tubular Structures as Platforms for Quantum Dots

The combination of top-down and bottom-up approaches offers great opportunities for the production of complex materials and devices. We demonstrate this approach by incorporating luminescent CdSe-ZnS nanoparticles into macroscopic tube structures that form as the result of externally controlled self-organization. The 1–2 mm wide hollow tubes consist of silica-supported zinc oxide/hydroxide and are formed by controlled injection of aqueous zinc sulfate into a sodium silicate solution. The primary growth region at the top of the tube is pinned to a robotic arm that moves upward at constant speed. Dispersed within the injected zinc solution are 3.4 nm CdSe-ZnS quantum dots (QDs) capped by DHLA-PEG–OCH₃ ligands. Fluorescence measurements of the washed and dried tubes reveal the presence of trapped QDs at an estimated number density of 10¹⁰ QDs per millimeter of tube length. The successful inclusion of the nanoparticles is further supported by electron microscopy and energy dispersive X-ray spectroscopy, with the latter suggesting a nearly homogeneous QD distribution across the tube wall. Exposure of the samples to copper sulfate solution induces quenching of about 90% of the tubes’ fluorescence intensity. This quenching shows that the large majority of the QDs is chemically accessible within the microporous, about 15-μm-wide tube wall. We suggest possible applications of such QD-hosting tube systems as convenient sensors in microfluidic and related applications