Abstract

Abstract

Abstract

In difference to compact objects of a similar size, toroidal structures have some distinguishing properties that originate from their open inner cavity and closed circuit. Here, a general facile methodology is developed to prepare composite rings with varied compositions on a large scale by using core-shell toroids assembled from tri-block copolymers of poly(4-vinyl pyridine) (PVP)/polystyrene (PS)/PVP. Taking advantage of the complexation ability of the PVP shell, varied components that range from polymers, inorganic materials, metals and their compounds, as well as pre-formed nanoparticles are introduced to the toroidal structures to form composite nanostructures. Metal ions can be adsorbed by PVP through complexation. After in situ reduction, a large number of metal-based functional materials can be prepared. PVP is alkaline, and thus capable of catalyzing the sol-gel process to generate an inorganic shell. Furthermore, pre-formed nanoparticles can also be absorbed by the shell through specific interactions. The PS core is not infiltrative during synthesis, and hollow rings can be derived after the polymer templates are removed.

Opal–inverse opal interlocked composites consisting of opals of hollow spheres with window channels interlocked, have displayed new properties. A facile and general method has been reported to synthesize the ordered composites. Polymer shells are first grown onto the surface of a silica sphere of an opal template by ATRP, which is followed by a sequential modification of the shells resulting in functional groups. Composite shells are favorably synthesized within the functional polymer shells. After the removal of silica opal templates, opal–inverse opal interlocked structures with varied compositions of polymers, inorganic materials, and carbon are achieved.

This report presents a facile approach for the low-temperature synthesis of crystalline inorganic-oxide composite hollow spheres by employing the bulk controlled synthesis of inorganic-oxide nanocrystals with polymer spheres as templates. The sulfonated polystyrene gel layer can adsorb the target precursor and induce inorganic nanocrystals to grow on the template in situ. The crystalline phase and morphology of the composite shell is tunable. By simply adjusting the acidity of the titania sol, crystalline titania composite hollow spheres with tunable crystalline phases of anatase, rutile, or a mixture of both were achieved. The approach is general and has been extended to synthesize the representative perovskite oxide (barium and strontium titanate) composite hollow spheres. The traditional thermal treatment for crystallite transformation is not required, thus intact shells can be guaranteed. The combination of oxide properties such as high refractive index, high dielectric constant, and catalytic ability with the cavity of the hollow spheres is promising for applications such as opacifiers, photonic crystals, high-κ-gate dielectrics, and photocatalysis.

Summary: A simple and efficient route to prepare inorganic compound/polymer composites in CO₂-based supercritical solution is presented. By this method, using polymeric hollow spheres as a substrate and Eu(NO₃)₃ as precursor, Eu₂O₃/polymer composites are successfully fabricated via the decomposition of the precursor in a supercritical CO₂/ethanol mixture at 120 °C. The resulting composites are characterized by means of transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It is indicated that besides being decorated on the outer surface of the polymer spheres, Eu₂O₃ nanoparticles are imbedded in the shell and further into the hollow cavity of the polymer spheres. The loading content and particle size of Eu₂O₃ on the polymer spheres can be controlled by changing the concentration of precursor in the solutions. The photoluminescence spectrum of the composites exhibit two peaks at 592 and 615 nm, which indicates that the composites can be used as optical material to emit red light. This method is also extended to the preparation of other inorganic compound/polymer composites with different functions.

Summary: Phenolic formaldehyde (PF) resins are attractive due to their excellent performances such as high temperature resistance, thermal abrasion, and high yield of carbon conversion. In this communication, PF resin-based composite hollow spheres were fabricated by in situ favorable absorption and catalytic crosslinking of PF resin within sulfonated polystyrene gel layers of the hollow sphere templates at low temperature. The composite hollow spheres were achieved in one step, avoiding traditional removal of template cores. The intact shell was tuned from double-layered to single-layered. Carbon hollow spheres with porous shell were derived by carbonization of the PF composite hollow spheres. Metal/carbon composite hollow spheres were further synthesized by the incorporation of metal within the porous shell, which would be a promising material for catalysis.

Hollow latex cages (HLCs) are used as templates to fabricate composite hollow spheres with complex structures. The template HLCs have a polystyrene shell with transverse hydrophilic channels connecting to an interior hydrophilic surface. They are stable and permeable, and a reagent can be preloaded into the cavity reservoir. The interior hydrophilic surface is conducive to a favorable inward synthesis. By simply altering the loading sequence of reagents and their concentration, the morphology of the composite spheres can be tuned. For example, during the formation of titania composite spheres by a sol–gel process using tetrabutyl titanate (TBT), composite hollow spheres with titania pillars protruding from the surface are predominantly created, owing to the formation of titania within the hydrophilic channels when the HLCs, preloaded with water, are immersed into TBT at an appropriate concentration. When the TBT concentration is decreased, the size of the pillars decreases accordingly until they disappear, leading to a smooth outer surface. Conversely, when HLCs loaded with TBT are immersed into water, titania forms only on the interior hydrophilic surface and not within the channels, resulting in composite hollow spheres with smooth outer surfaces. The composite spheres can be further used as templates to grow material on the outer surface, and double-shelled hollow spheres of various compositions are achieved. Macroporous materials with unique morphologies—for example, hollow spheres embedded within the pores—have been derived by using an array template of the composite spheres. The method can be applied to a diversity of inorganic materials, metals, oxides, semiconductors, and functional polymers.

Summary: Crosslinkable composite microspheres were prepared by heterocoagulation of epoxy resin nanoparticles onto polystyrene microspheres. The corresponding hollow microspheres were created after removal of the core. The surface morphology was tunable from smooth to rough by controlling the degree of crosslinking of the shell nanoparticles. A positively charged polyelectrolyte could be easily adsorbed onto the composite microspheres to facilitate further synthesis, e.g., layer-by-layer deposition and a sol-gel process to form inorganic materials.

Doppelagent: Die kontrollierte Sulfonierung von Polystyrolhohlkugeln liefert hydrophile Schichten mit Sulfonsäuregruppen, über die eine große Vielfalt an funktionellen Kompositmaterialien zugänglich sind. So wurden unter Verwendung solcher sulfonierter Polystyrolhohlkugeln als Template doppelschalige Hohlkugeln (siehe TEM-Bild einer Titanoxidkugel) in einem Schritt erhalten.

Summary: Core/shell opal gels of sulfonated polystyrene were used as templates to synthesize structured crystalline titania materials. Under acidic conditions, opal materials with hollow spheres of controllable shell thickness and cavity size were prepared. Under neutral conditions, inverse opal inorganic materials with a tunable pore size were prepared. It is crucial that proton ions induce a preferential sol/gel process, forming titania in the gel.

Pulling the rug out! A templated electrodeposition technique has been applied to prepare stable 3D, organized networks of metal or semiconductor nanowires (see scheme). The process involves a) the deposition of mesoporous silica onto an electrode, b) the introduction of metals or semiconductors into the pore channels, and c) removal of the silica template to yield the nanowire network.

Freigelegt! Mit einer templatgestützten Elektroabscheidung gelang die Synthese stabiler Netzwerke aus Metall- oder Halbleiternanodrähten (siehe Schema). Dazu wurde a) mesoporöses Siliciumdioxid an einer Elektrode abgeschieden, b) die Kanäle mit dem Metall oder Halbleiter gefüllt und c) das Templat entfernt, um das Nanodrahtnetz zu erhalten.

In this paper, we report on the preparation of monodisperse polyaniline (PANi)–silica composite capsules and hollow spheres on monodisperse core–gel-shell template particles. An extension of the previously reported inward growth method was used. The samples were self-stabilized without external additives. The core–gel-shell particles were prepared by the inward sulfonation of monodisperse polystyrene particles. The introduced sulfonic acid and sulfone groups are responsible for the gel properties. The gel-shell thickness and core size were synchronously controlled over the whole particle radius range. After aniline (ANi) monomer was preferentially absorbed in the sulfonated polystyrene shell, PANi was formed by polymerization. PANi was doped in situ with a sulfonic acid group to give the capsules a high conductivity. PANi hollow spheres were derived after the polystyrene cores were dissolved: their cavity size and shell thickness were synchronously controlled by using different core–gel-shell particles. The PANi–silica composite capsules and hollow spheres were therefore prepared by a sol–gel process using tetraethylorthosilicate in the conducting shell. The PANi shell became more robust while maintaining the same conductivity level. Morphological results indicate that the PANi and silica formed a bicontinuous network. Fourier-transform infrared (FTIR) spectra revealed that the hydrogen bonding in the PANi–gel shell was enhanced after the silica phase was incorporated, which could explain the high conductivity level after the silica phase was added. In a converse procedure, silica capsules and hollow spheres were prepared by a sol–gel process that incorporated tetraethylorthosilicate into the core–gel-shell templates, which was followed by the absorption and polymerization of aniline in the silica shell thus forming PANi–silica composite capsules and hollow spheres. The silica capsules and hollow spheres thereby became conductive.

Nanostructured graphitelike carbon films are prepared through a simple pyrolysis method. The as-prepared films are superhydrophobic for not only pure water but also corrosive liquids, such as acidic and basic solutions. The picture shows water droplets with pH values of 1.07 (left) and 13.76 (right) in contact with a nanostructured carbon film. This is the first example of superhydrophobicity over the whole range of pH values, without the presence of fluorine-containing compounds.

Taking control: One-dimensional mesostructured silica materials and their arrays are prepared in anodic alumina membranes. By adjusting the wettability of the alumina pore wall, nanofibers and nanotubes are prepared in a controlled way. The mesostructured silica morphology (see picture) can be adjusted by changing the surfactant concentration. Both the mesopores and the tubular cavities can be incorporated with functional materials, thus forming hierarchical nanocomposites.

Nanostrukturierte graphitartige Kohlenstoff-Filme lassen sich mithilfe einer einfachen Pyrolysemethode herstellen. Ohne Weiterbehandlung erhält man Filme, die nicht nur Wasser abweisen, sondern auch ätzende Flüssigkeiten wie saure oder basische Lösungen. Das Bild zeigt Wassertropfen mit pH-Werten von 1.07 (links) und 13.76 (rechts) im Kontakt mit einem nanostrukturierten Kohlenstoff-Film. Dies ist das erste Beispiel für Superhydrophobie über einen weiten pH-Bereich in Abwesenheit fluorhaltiger Verbindungen.

Kontrollierte Formgebung: Eindimensionales mesostrukturiertes Siliciumdioxid wird mithilfe von Aluminiumoxidmembranen aufgebaut. Die Benetzungseigenschaften der porösen Aluminiumoxidschicht sind dabei entscheidend für die gezielte Herstellung von Nanofasern und Nanoröhren; die Konzentration eines Tensides bestimmt die Morphologie des mesostrukturierten Siliciumdioxids (siehe Bild). Durch Einlagerung funktioneller Substrate in Mesoporen und röhrenförmige Hohlräume können hierarchische Nanokomposite hergestellt werden.