CdS‐Nanoparticle/Polymer Composite Shells Grown on Silica Nanospheres by Atom‐Transfer Radical Polymerization

In this paper we describe the combined use of surface‐initiated atom transfer radical polymerization (ATRP) and a gas/solid reaction in the direct preparation of CdS‐nanoparticle/block‐copolymer composite shells on silica nanospheres. The block copolymer, consisting of poly(cadmium dimethacrylate) (PCDMA) and poly(methyl methacrylate) (PMMA), is obtained by repeatedly performing the surface‐initiated ATRP procedures in N,N‐dimethylformamide (DMF) solution at room temperature, using cadmium dimethacrylate (CDMA) and methyl methacrylate (MMA) as the monomers. CdS nanoparticles with an average size of about 3 nm are generated in situ by exposing the silica nanospheres coated with block‐copolymer shells to H₂S gas. These synthetic core–shell nanospheres were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), diffuse reflectance UV‐vis spectroscopy, X‐ray photoelectron spectroscopy (XPS), and powder X‐ray diffraction (XRD). These composite nanospheres exhibit strong red photoluminescence in the solid state at room temperature.     

Dual‐Functionalized Polymer Nanotubes as Substrates for Molecular‐Probe and DNA‐Carrier Applications

Bifunctionalized polymer nanotubes have been fabricated using vapor‐deposition polymerization in FeCl₃‐adsorbed anodic aluminum oxide membranes followed by attachment of amine‐functionalized silica nanoparticles. The prepared bifunctionalized polymer nanotubes are applied as both a molecular probe and a DNA carrier by conjugating pyreneacetic acid with the amine groups and immobilizing DNA with the carboxylic acid groups on the surface. The number of amine functional groups on the nanotubes' surface can be measured by means of the photoluminescence intensity of pyreneacetic acid conjugated with amine groups, and the number of the residual carboxylic acid groups is calculated by titration with sodium hydroxide. Fourier‐transform infrared spectroscopy, X‐ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, and confocal laser scanning microscopy have been performed to confirm the complete polymerization of the monomer and the attachment of photoluminescent molecules and single‐stranded DNA.     

Surface‐Confined Atom Transfer Radical Polymerization from Sacrificial Mesoporous Silica Nanospheres for Preparing Mesoporous Polymer/Carbon Nanospheres with Faithful Shape Replication: Functional Mesoporous Materials

A facile approach for the preparation of mesoporous polymer nanospheres (MPN) and mesoporous carbon nanospheres (MCN) with complete shape retention based on surface‐confined atom transfer radical polymerization of various methacrylate monomers from in situ generated initiator‐modified hard silica nanospheres template is developed. This approach yields mesoporous silica‐polymer hybrid nanospheres (MSPN) with mesopores that are uniformly filled with covalently attached well‐defined poly(methacrylate)s. The silica frameworks are subsequently etched, resulting in MPN. Pyrolysis of MSPN and subsequent removal of silica template resulted in the production of MCN. They retain the size, shape, and mesoporous ordering of the silica template nanospheres. Gel permeation chromatography analysis of the silica free polymers reveals that they have controlled molecular weights and low polydispersities (PDIs). Kinetics studies reveal that the molecular weight of the grafted polymer increases linearly with time, maintaining low PDIs, indicating the living nature of the polymerization. The mesoporous polymer material is found to have low dielectric constant, which paves the way for their use as low‐dielectric constant materials in microelectronics. This approach allows fabrication of functional MPN using functional comonomers, which are successfully used for the synthesis of “clickable” mesoporous polymer nanospheres, removal of ionic contaminates through anion exchange, and glucose sensing.     

Fabrication of a Highly Transparent Conductive Thin Film from Polypyrrole/Poly(methyl methacrylate) Core/Shell Nanospheres

Polypyrrole (PPy)/poly(methyl methacrylate) (PMMA) core/shell nanospheres with diameters of several tens of nanometers have been synthesized by two‐step microemulsion polymerization, and highly transparent conductive thin films have been fabricated using the nanospheres as a filler in a PMMA matrix. The PPy/PMMA core/shell nanoparticles and their composite films have been extensively characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDX), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier‐transform infrared (FT‐IR) and UV‐vis spectroscopies, and electrical‐conductivity measurements. The fabricated polymer films containing the PPy/PMMA core/shell nanofillers show a much better transparent conductive performance than that of uncoated PPy nanoparticles with similar dimensions or bulk PPy particles with diameters of several hundreds of nanometers. The PMMA shell promotes compatibility of the conductive fillers with the PMMA matrix and enhances dispersion of the PPy/PMMA core/shell nanofillers. In addition, the nanometer‐thick PMMA shell has a lower glass‐transition temperature (T_g), and can be effectively annealed to form a conductive‐filler network with a high electrical conductivity at a relatively low filler content.     

Optical Control and Patterning of Gold‐Nanorod–Poly(vinyl alcohol) Nanocomposite Films

Gold nanorods with well‐defined aspect ratios are homogeneously incorporated within poly(vinyl alcohol) thin films and subsequently aligned by heating and stretching the nanocomposite films. The spatial alignment of the nanorods is directly proved using transmission electron microscopy. The polarization‐dependent optical response of the rods is measured and compared with a dipole model. Excellent agreement is found. Additionally, irradiation of the film with nanosecond laser pulses (1064 nm) leads to selective reshaping of the nanorods into nanospheres, and we demonstrate that this effect can be used to micropattern optical structures into the films.     

Inside Front Cover: Optical Control and Patterning of Gold‐Nanorod–Poly(vinyl alcohol) Nanocomposite Films (Adv. Funct. Mater. 7/2005)

The micropatterning of optical structures into thin films of poly (vinyl alcohol) (PVA) containing gold nanorods is demonstrated by Pérez‐Juste, Liz‐Marzán, and co‐workers on p. 1065. The nanorods are uniformly distributed in the thin films and can be aligned by stretching the films. The inside cover shows how irradiation with a nanosecond laser, using a TEM grid as mask, selectively reshapes the nanorods into nanospheres (upper and lower TEM images, respectively). Gold nanorods with well‐defined aspect ratios are homogeneously incorporated within poly(vinyl alcohol) thin films and subsequently aligned by heating and stretching the nanocomposite films. The spatial alignment of the nanorods is directly proved using transmission electron microscopy. The polarization‐dependent optical response of the rods is measured and compared with a dipole model. Excellent agreement is found. Additionally, irradiation of the film with nanosecond laser pulses (1064 nm) leads to selective reshaping of the nanorods into nanospheres, and we demonstrate that this effect can be used to micropattern optical structures into the films.     

Self-assembly fabrication of ZnO hierarchical micro/nanospheres for enhanced photocatalytic degradation of endocrine-disrupting chemicals

ZnO hierarchical micro/nanospheres were successfully synthesized via a facile and surfactant-free chemical solution route. The field emission scanning electron microscopy and transmission electron microscopy observations showed that the ZnO micro/nanospheres were assembled by large amounts of interleaving nanosheets with the thickness of about 17 nm. The X-ray diffraction, energy dispersion X-ray and Raman results revealed that the as-synthesized products were well-crystalline and possessing wurtzite hexagonal phase pure ZnO. Under UV irradiation, the ZnO micro/nanospheres showed an enhanced photocatalytic performance compared with the ZnO nanorods and commercial TiO₂ in the degradation of phenol. The photocatalytic enhancement of ZnO micro/nanospheres was attributed to their unique hierarchical porous surface structure and large surface area which can enhance the electron–hole separation and increased the yield of hydroxyl radical quantities as evidenced by the photoluminescence spectra. By using a certain of radical scavengers, hydroxyl radical was determined to play a pivotal role for the phenol degradation. Moreover, the as-synthesized ZnO micro/nanospheres could be easily recycled without any significant loss of the photocatalytic activity. Other endocrine-disrupting chemicals such as resorcinol, bisphenol A and methylparaben were also successfully photodegraded under identical conditions. These characteristics showed the practical applications of the ZnO micro/nanospheres in environmental remediation.     

Self‐Supporting,Double Stimuli‐Responsive Porous Membranes From Polystyrene‐block‐poly(N,N‐dimethylaminoethyl methacrylate) Diblock Copolymers

Asymmetric membranes are prepared via the non‐solvent‐induced phase separation (NIPS) process from a polystyrene‐block‐poly(N,N‐dimethylaminoethyl methacrylate) (PS‐b‐PDMAEMA) block copolymer. The polymer is prepared via sequential living anionic polymerization. Membrane surface and volume structures are characterized by scanning electron microscopy. Due to their asymmetric character, resulting in a thin separation layer with pores below 100 nm on top and a macroporous volume structure, the membranes are self‐supporting. Furthermore, they exhibit a defect‐free surface over several 100 µm². Polystyrene serves as the membrane matrix, whereas the pH‐ and temperature‐sensitive minority block, PDMAEMA, renders the material double stimuli‐responsive. Therefore, in terms of water flux, the membranes are able to react on two independently applicable stimuli, pH and temperature. Compared to the conditions where the lowest water flux is obtained, low temperature and pH, activation of both triggers results in a seven‐fold permeability increase. The pore size distribution and the separation properties of the obtained membranes were tested through the pH‐dependent filtration of silica particles with sizes of 12–100 nm.     

A Precursor‐Based Route to ZnSe Nanowire Bundles

A large number of one‐dimensional bundles of ZnSe nanowires with diameters ranging from 15–20 nm and lengths of up to tens of micrometers have been prepared via the thermal treatment of a ribbon‐like precursor (ZnSe·3ethylenediamine), which has been synthesized by a mixed solvothermal route, in an argon atmosphere. The as‐obtained precursor has been characterized by powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), IR spectroscopy, thermogravimetric analysis, and elemental analysis. XRD and high‐resolution TEM characterization reveal that the as‐synthesized ZnSe nanowires have the single‐crystal hexagonal wurtzite structure with the [001] growth direction. The surface chemical composition of ZnSe nanowires has been studied by X‐ray photoelectron spectroscopy. The cooperative action of the mixed solvents may be responsible for the formation of the morphology of the resulting products. Room‐temperature photoluminescence measurements indicate the as‐grown ZnSe nanostructures have a strong emission peak centered at 587 nm and two weak emission peaks centered at 435 and 462 nm. The strong emission from the ZnSe nanostructures reveals their potential as building blocks for optoelectronic devices.     

Plasmon-loss imaging of chains of crystalline-silicon nanospheres and silicon nanowires

Nanostructures in chains of crystalline-silicon nanospheres and silicon nanowires were investigated using energy-filtered transmission electron microscopy (TEM). Observation of the shape of the silicon nanospheres in the chains provided the direct evidence that the chains were formed via the surface oxidation process, which may preferentially work at the necks. The diverse nanostructures in silicon nanowires were revealed, and we found smooth-shaped wires which have periodically modulated silicon cores. Nanostructures in wire-chain transition regions were also investigated for the first time. The wire-chain transition is not a simple junction of a silicon nanowire and a chain of silicon nanospheres, but has a periodically modulated silicon core in the wire region near the transition position.     

From Layered Basic Zinc Acetate Nanobelts to Hierarchical Zinc Oxide Nanostructures and Porous Zinc Oxide Nanobelts

Novel hierarchical ZnO nanostructures, porous ZnO nanobelts, and nanoparticle chains are prepared from a precursor of synthetic bilayered basic zinc acetate (BLBZA) nanobelts. BLBZA nanobelts are obtained by a simple synthetic route under mild conditions. X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, and thermal analysis are used to characterize the BLBZA nanobelts and ZnO nanostructures. The obtained BLBZA precursor consists of a lamellar structure with two interlayer distances of 1.33 and 2.03 nm, exhibits a beltlike morphology, and has widths of 200 to 600 nm, thicknesses of 10 to 50 nm, and lengths of up to 50 μm. Refluxing an aqueous dispersion of BLBZA nanobelts at 120 °C for 12 h leads to the formation of well‐defined hierarchical ZnO nanostructures. The time‐dependent shape‐evolution process suggests that spindlelike ZnO particles form first, and then the ringlike nanosheets grow heterogeneously on the backbone of these spindles. In addition, calcination in air can remove ligand molecules and intercalated water molecules from BLBZA nanobelts, resulting in the formation of porous ZnO nanobelts and nanoparticle chains. The BLBZA nanobelts serve as templates during the transformation to form ZnO beltlike nanoparticle chains without morphological deformation. Photoluminescence results show that both the as‐synthesized hierarchical ZnO nanostructures and porous ZnO nanobelts show a narrow and sharp UV emission at 390 nm and a broad blue–green emission at above 466 nm when excited by UV light.     

Polyaniline–Silica Composite Conductive Capsules and Hollow Spheres

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.     

A Ligand Exchange Route to Highly Luminescent Surface‐Functionalized ZnS Nanoparticles and Their Transparent Polymer Nanocomposites

A facile ligand exchange approach for surface‐functionalized ZnS nanoparticles (NPs) with 5‐(2‐methacryloylethyloxymethyl)‐8‐quinolinol (MQ) is described. The MQ–ZnS NPs, with a cubic crystal structure, have the same diameter as ZnS NPs without MQ about 3.0 nm. The MQ–ZnS NPs exhibit strong fluorescence emission at about 500 nm and a high photoluminescence (PL) quantum yield (QY), up to 40%, with a decreasing ratio of MQ to ZnS NPs. The PL decay study reveals that the lifetimes of the different MQ–ZnS NPs with a single exponential decay are in the nanosecond time domain for emission at about 500 nm, which is obviously different from that of ZnS NPs with a biexponential decay for defect‐state emission at 420 nm. The functionalized MQ–ZnS NPs are successfully incorporated into the polymer matrix by in situ bulk polymerization to fabricate transparent bulk nanocomposites with good thermal stability and processability. Transmission electron microscopy results show that the NPs are uniformly dispersed in the polymer matrix without aggregation. The good PL properties of MQ–ZnS NPs are preserved in the bulk nanocomposites. It is observed that the nanocomposites have red‐shifted excitation and emission wavelengths compared with those of both the polymer matrix and MQ–ZnS NPs, possibly because of the cooperative interaction between MQ–ZnS NPs and the polymer matrix with blue emission.     

Fabrication and Characterization of Two‐Photon Polymerized Features in Colloidal Crystals

The fabrication and characterization of two‐photon polymerized features written within and outside of colloidal crystals is presented. Two‐photon polymerization (TPP) response diagrams are introduced and developed to map the polymerization and damage thresholds for features written via modulated beam rastering. The use of tris[4‐(7‐benzothiazol‐2‐yl‐9,9‐diethylfluoren‐2‐yl)phenyl]amine (AF‐350) as an initiator for TPP is demonstrated for the first time and TPP response diagrams illustrate the polymerization window. These diagrams also demonstrate that the polymerization behavior within and outside of colloidal crystals is similar and electron microscopy reveals nearly identical resolution. Fluorescence confocal microscopy further enables visualization of non‐self‐supporting, three‐dimensional TPP features within self‐assembled photonic crystals. Finally, microspot spectroscopy is collected from a two‐photon feature written within a colloidal crystal and this is compared with simulation.     

Mesostructured Arrays of Nanometer‐spaced Gold Nanoparticles for Ultrahigh Number Density of SERS Hot Spots

A novel one‐trough synthesis via an air‐water interface is demonstrated to provide hexagonally packed arrays of densely spaced metallic nanoparticles (NPs). In the synthesis, a mesostructured polyoxometalate (POM)‐silicatropic template (PSS) is first self‐assembled at the air‐water interface; upon UV irradiation, anion exchange cycles enable the free‐floating PSS film to continuously uptake gold precursors from the solution subphase for diffusion‐controlled and POM‐site‐directed photoreduction inside the silica channels. NPs ≈ 2 nm can hence be homogeneously formed inside the silica‐surfactant channels until saturation. As revealed via X‐ray diffraction, small‐angle X‐ray scattering (SAXS), grazing incidence SAXS, and transmission electron microscopy, the Au NPs directed by the PSS template are arrayed into a 2D hexagonal lattice with inter‐channel spacing of 3.2 nm and a mean along‐channel NP spacing of 2.8 nm. This corresponds to an ultra‐high number density (≈10¹⁹ NPs cm^?3) of narrowly spaced Au NPs in the Au‐NP@PSS composite, leading to 3D densely deployed hot‐spots along and across the mesostructured POM‐silica channels for surface‐enhanced Raman scattering (SERS). Consequently, the Au‐NP@PSS composite exhibits prominent SERS with 4‐mercaptobenzoic acid (4‐MBA) adsorbed onto Au NPs. The best 4‐MBA detection limit is 5 nm , with corresponding SERS enhancement factors above 10⁸.     

Nanoporous Ultra‐Low‐Dielectric‐Constant Fluoropolymer Films via Selective UV Decomposition of Poly(pentafluorostyrene)‐block‐Poly(methyl methacrylate) Copolymers Prepared Using Atom Transfer Radical Polymerization

Block copolymers of poly(pentafluorostyrene) (PFS) and poly(methyl methacrylate) (PMMA) (PFS‐b‐PMMA) have been synthesized using atom transfer radical polymerization (ATRP). Then, nanoporous fluoropolymer films have been prepared via selective UV decomposition of the PMMA blocks in the PFS‐b‐PMMA copolymer films. The chemical composition and structure of the PFS homopolymers and copolymers have been characterized using nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), X‐ray photoelectron spectroscopy (XPS), time‐of‐flight secondary‐ion mass spectrometry (ToF‐SIMS), and molecular‐weight measurements. The cross‐sectional and surface morphologies of the PFS‐b‐PMMA copolymer films before and after selective UV decomposition of the PMMA blocks have been studied using field‐emission scanning electron microscopy (FESEM). The nanoporous fluoropolymer films with pore sizes in the range 30–50 nm and porosity in the range 15–40 % have been obtained from the PFS‐b‐PMMA copolymers of different PMMA content. Dielectric constants approaching 1.8 have been achieved in the nanoporous fluoropolymer films which contain almost completely decomposed PMMA blocks.     

Photo‐Induced Functionalization of Spherical and Planar Surfaces via Caged Thioaldehyde End‐Functional Polymers

The synthesis and application of a novel reversible addition‐fragmentation chain transfer (RAFT) agent carrying a photocaged thioaldehyde moiety is described (λ_max = 355 nm). RAFT polymerization of styrene, dimethylacrylamide and a glycomonomer is evidenced (3600 g mol^?1 ≤ M_n ≤ 15 000 g mol^?1; 1.07 ≤ ? ≤ 1.20) with excellent end‐group fidelity. The photogenerated thioaldehyde on the chain ends can undergo hetero Diels–Alder reactions with dienes as well as reactions with nucleophiles. The terminal photoreactive polymers are photografted to porous diene‐reactive polymeric microspheres. The grafted particles are in‐depth characterized via scanning electron microscopy, elemental analysis, X‐ray photoelectron spectroscopy, and high resolution FT‐IR microscopy, leading to a qualitative as well as quantitative image of the core–shell objects. Grafting densities up to 0.10 molecules nm^?2 are reached. The versatility of the thioaldehyde ligation is evidenced by spatially resolved grafting of polystyrene onto nucleophilic groups present in poly (dopamine) (PDA)‐coated glass slides and silicon wafers via two‐photon direct laser writing (DLW) imaged by ToF‐SIMS. The combination of thioaldehyde ligation, RAFT polymerization, and DLW allows for the spatially resolved grafting of a vast range of polymers onto various substrates in any desired pattern with sub‐micrometer resolution.     

The First Template‐Free Growth of Crystalline Silicon Microtubes

A simple template‐free high‐temperature evaporation method was developed for the growth of crystalline Si microtubes for the first time. As‐grown Si microtubes were characterized using X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and room‐temperature photoluminescence. The lengths of the Si tubes can reach several hundreds of micrometers; some of them have lengths on the order of millimeters. Each tube has a uniform outer diameter along its entire length, and the typical outer diameter is ≈ 2–3 μm. Most of the tubes have a wall thickness of ≈ 400–500 nm, though a considerable number of them exhibit a very thin wall thickness of ≈ 50 nm. Room‐temperature photoluminescence measurement shows the as‐synthesized Si microtubes have two strong emission peaks centered at ≈ 589 nm and ≈ 617 nm and a weak emission peak centered at ≈ 455 nm. A possible mechanism for the formation of these Si tubes is proposed. We believe that the present discovery of the crystalline Si microtubes will promote further experimental studies on their physical properties and smart applications.     

Fabrication and Spatially Resolved Functionalization of 3D Microstructures via Multiphoton‐Induced Diels–Alder Chemistry

Three‐dimensional microstructures are fabricated utilizing direct laser writing combined with a non‐radical step polymerization based on multiphoton‐induced Diels–Alder chemistry of o‐quinodimethanes and maleimides. Woodpile photonic crystals with a total of five axial periods and a rod spacing of down to 500 nm are fabricated. The structures are characterized via scanning electron microscopy and focused ion beam milling. In addition, corresponding photonic stop bands are investigated via light microscopy as well as transmission and reflection spectroscopy. The Diels–Alder based network formation during direct laser writing is verified via infrared spectroscopy. Spatially resolved surface patterning of covalently bonded functional molecules on fabricated structures is demonstrated by employing the direct laser writing setup and a bromine containing maleimide. The successful surface modification is verified via time‐of‐flight secondary ion mass spectrometry.     

Synthesis and photoluminescence properties of CdS hollow nanospheres by chemical vapor deposition

High-density CdS hollow nanospheres are successfully synthesized by a simple chemical vapor deposition technology.The crystal structure,compositional information,and morphological structure are characterized by X-ray diffraction(XRD),scanning electronic microscopy(SEM),transmission electronic microscopy(TEM),and energy-dispersive X-ray spectrometer(EDX).The results show that the as-prepared CdS hollow nanospheres have uniform size about 1-3 μm in diameter.The Kirkendall phenomenon is proposed for the formation of the CdS nanostructures.A strong emission located at 580 nm is observed.