Fourteen different "hairy-rod" conjugated polymers, 9,9-dioctylfluorene derivatives entailing 1,2,3-triazole, azomethine, ethynyle, biphenyle, stilbene, and azobenzene lateral units, are synthesized via modular conjugation and are systematically investigated with respect to their ability to selectively disperse SWCNTs. Four polymers of the azomethine type, with unprecedented selectivity toward dispersing (8,7), (7,6), and (9,5) SWCNT species, have been identified. In particular, azomethine polymers, herein applied for the first time for SWCNT dispersion, have been evidenced to be very effective in the highly selective solubilization of SWCNTs. The experimentally observed selectivity results are unambiguously supported by molecular dynamics simulations that account for the geometrical properties and deformation energy landscape of the polymer. Specifically, the calculations accurately and with high precision predict the experimentally observed selectivity for the (7,6) and (9,5) conformations.

With the long term aim of preparing synthetic macromolecules that mimic the folding actions of natural biomacromolecules, a single synthetic polymer chain containing two distinct and orthogonal hydrogen bonding recognition motifs has been synthesized using an atom transfer radical polymerization (ATRP) and orthogonal ligation strategy. The hydrogen bonding recognition units, based on both three-point thymine (Thy)-diaminopyridine (DAP) and six-point cyanuric acid (CA)-Hamilton wedge (HW) interactions, induced - at low concentrations - a single chain self-folding process. The self-assembly process was monitored - initially between small molecule models - by proton nuclear magnetic resonance ( 1H NMR) spectroscopy, revealing full orthogonality of the two recognition pairs, HW-CA and Thy-DAP. Dynamic as well as static light scattering (DLS and SLS) analyses of the macromolecular self-assembly systems provide unambiguous evidence for the hydrogen-bonding interactions between both the Thy-DAP and CA-HW units leading to well-defined dual point single chain self-folding, indicating that more complex single chain self-assemblies based on synthetic polymers should be able to mimic - on a simplified level - the folding actions of natural biomacromolecules. The reversibility of the self-folding action depends on temperature as confirmed via 1H-NMR spectroscopy in [D 2]tetrachloroethane. © 2012 The Royal Society of Chemistry.

To date synthetic methods to selectively produce specific (n, m) single-walled carbon nanotubes (SWCNTs) are not available. Therefore, post-processing of SWCNTs including solubilization and sorting by metallicity, length, diameter, chirality or (n, m) is necessary for further applications. To reach the goal of sorting SWCNTs, we have synthesized various conjugated polymers consisting of alternating 9,9-dialkyl fluorene and 1,2,3-triazole units via copper catalyzed alkyne–azide conjugation chemistry. Their ability to selectively wrap specific (n, m) SWCNTs is investigated towards HiPco SWCNT raw materials which contain more than 40 (n, m) species and are found to be comparable to fluorene based triazole free polymers, which are typically prepared via Suzuki-type polymerization. However, the herein reported triazole-linked click polymers are significantly simpler to prepare than their Suzuki-analogs. Fluorescence and UV/Vis NIR spectroscopy were employed to analyze the SWCNTs–polymer suspensions and demonstrate their selectivity for dispersing SWCNTs.

Silicon substrates coated with a bromide-terminated silane are transformed into highly reactive, cyclopentadiene covered analogues. These surfaces undergo rapid cycloaddition reactions with various dienophile-capped polymers. Mild heating of the substrates causes the retro-Diels-Alder reaction to occur, thus reforming the reactive cyclopentadiene surface, generating an efficiently switchable surface.

To study the crystallization kinetics of β-Si3N4in Si–B–C–N polymer-derived ceramics, the amorphous ceramics with composition SiC1.6N1.0B0.4were synthesized and then isothermally annealed at 1700, 1775 and 1850 °C. The integrated intensities of β-Si3N4x-ray diffraction (XRD) patterns were used to examine the course of crystallization. The average size of the Si3N4nanocrystallites was analyzed by means of the XRD measurements and energy-filtering transmission electron microscopy. It was realized that the nanocrystallite dimensions change insignificantly within the time period of crystallization; however, they depend significantly on the temperature. Subsequently, the kinetics of the β-Si3N4crystallization was analyzed. Consequently, large activation energy in the range of 11.5 eV was estimated. Moreover, continuous nucleation and diffusion-controlled growth have been concluded as the main mechanisms of the crystallization process. Further analysis points at the crucial role of the nucleation rate in the crystallization kinetics of β-Si3N4.

The first RAFT mediated polymerization of methyl methacrylate initiated by diradicals derived from Bergman cyclization was performed employing 3,4-benzocyclodec-3-ene-1,5-diyne (BCDY) as diradical source and cyanoisopropyldithiobenzoate (CPDB) as RAFT agent. The polymerization was conducted in bulk at 80 °C for 3 h. The concentration of the enediyne was kept constant at 3.0 x 10⁻² mol · L⁻¹ and the RAFT agent concentration was varied between 0.0 mol · L⁻¹ and 2.4 x 10⁻¹ mol · L⁻¹. A detailed ESI-MS analysis reveals the absence of intramolecular termination reactions (ring formation) in the RAFT mediated system, which usually makes diradicalic initiation unfavorable. The presence of polymeric chains propagating at both ends could be confirmed. The conversion of the RAFT mediated polymerization was up to more than two times higher than the RAFT free polymerization at identical conditions. Thus, polymers with narrow polydispersities (1.1 ≤ PDI ≤ 1.5) even at very high molecular weights (near 400,000 Da) were obtained within modest reaction times.

Amorphous Si–B–C–N polymer‐derived ceramics (PDCs) with 8.3 at.% of boron were synthesized by thermolysis of the boron‐modified poly(methylvinylsilazane). The isochronal crystallization process was quantitatively studied by X‐ray diffraction (XRD) measurements using variable heating rates. Crystalline structures form within the amorphous Si–B–C–N PDCs at two stages including the formation of nanocrystalline SiC (NC‐SiC) at the first stage followed by the formation of nanocrystalline Si3N4 (NC‐Si3N4) and additional NC‐SiC at the second stage. The change of the SiC crystallite size with temperature determined from the XRD analysis was used as a part of input data for the modeling. The metastable phase fraction diagrams were computed using an available model of metastable phase equilibria including amorphous and nanocrystalline phases for various modeling parameters and variable heating rates as well. The modeling performed is consistent with the experimental results to a large extent. The impact of modeling free parameters is discussed in order to explain the discrepancies observed between the experimental and computational results. The extended study of the NC‐SiC formation at the first stage of crystallization justifies that this process is not purely controlled by kinetics and proves a crucial role of the metastable phase equilibrium between the amorphous Si–C–N domains and NC‐SiC.

Physico-chemical methods to sort single-walled carbon nanotubes (SWNTs) by chiral index are presently lacking but are required for in-depth experimental analysis and also for potential future applications of specific species. Here we report the unexpected selectivity of poly(N-decyl-2,7-carbazole) to almost exclusively disperse semiconducting SWNTs with differences of their chiral indices (n - m) ≥ 2 in toluene. The observed selectivity complements perfectly the dispersing features of the fluorene analogue poly(9,9-dialkyl-2,7-fluorene), which disperses semiconducting SWNTs with (n - m) ≤ 2 in toluene. The dispersed samples are further purified by density gradient centrifugation and analyzed by photoluminescence excitation spectroscopy. All-atom molecular modeling with decamer model compounds of the polymers and (10,2) and (7,6) SWNTs suggests differences in the π-π stacking interaction as origin of the selectivity. We observe energetically favored complexes between the (10,2) SWNT and the carbazole decamer and between the (7,6) SWNT and the fluorene decamer, respectively. These findings demonstrate that subtle structural changes of polymers lead to selective solvation of different families of carbon nanotubes. Furthermore, chemical screening of closely related polymers may pave the way toward simple, low-cost, and index-specific isolation of SWNTs.

Lithographically defined self-growing ZnO films were prepared by a bioinspired chemical bath deposition technique (CBD). We observed a high selectivity of ZnO deposition: Teflon-like per-fluoro-decyl-trichlorosilane (FDTS) monolayers repelled ZnO primary particles, whereas amino-functionalized areas of the substrate were selectively covered by a highly anisotropic, oriented, and compact ZnO film with a thickness of 50 nm. The size of the primary particles in our methanol-based solution was approximately 2.5 nm. On the amino substrate they formed agglomerates not larger than 30 nm. Monolayer patterns made by polymer blend lithography were templated with an edge resolution of 30 nm. By using a specialized derivative of microcontact printing, we prepared layout-defined silane templates, which reliably determined the growth of a layout-defined, patterned oxide film with submicrometer lateral resolution.

Alpha,omega-hydrogen donor/acceptor functional polymer strands are prepared via a combination of living radical polymerization and orthogonal conjugation and subsequently self-assembled as single chains to emulate--on a simple level--the self-folding behaviour of natural biomacromolecules.

TiO2 nanopowders have been synthesized from a peroxotitanium solution chemical bath route. The variation of H+ concentrations of the reaction solutions was measured during the course of the synthesis. X-ray diffraction analysis and transmission electron microscope observation showed that peroxotitanium concentration can affect the crystal type and morphology of the TiO2 nanopowders. The particle size of TiO2 nanopowders prepared from 0.1molL−1 peroxotitanium is 7.7nm. The specific surface area of this nanopowder is 250m2g−1. Thermogravimetric analysis showed that the TiO2 nanopowder dried at 80°C for 24h contains 11% water.

An efficient and mild modification of Si surfaces through orthogonal hetero Diels-Alder (HDA) chemistry, was investigated. The modification of Si wafers was achieved by the silanization of pretreated Si surfaces using 3-(N-strylmethyl-2-aminoethylamino)-propyl trimethoxy silane (SM-TMS). The RAFT-HDA reaction between the PSDTF functionalized PiBA and the styryl functionalized Si surface proceeds in the absence of catalysts at 60°C. The coupling reaction between Si surfaces modified with a styrene linker and PiBA-PSDTF was performed at 60° C in chloroform solution within 12 h. The conjugation leads to the formation of a 3,6-dihydro-2H-thiopyran ring, the stability of which has been investigated and found to be withstanding relatively harsh conditions of pH and heat. The surface modification was also confirmed by measuring the thickness through ellipsometry of the Si wafers after hydrolsis.

In this paper, we report a novel synthetic approach towards electrically conductive ZnO nanowires close to ambient conditions using λ-DNA as a template. Initially, the suitability of DNA to assemble ZnO nanocrystals into thin coatings was investigated. The ZnO nanowires formed on stretched and aligned λ-DNA molecules were prepared via chemical bath deposition (CBD) of zinc acetate in methanol solution in the presence of polyvinylpyrrolidone (PVP). After 10 deposition cycles, the nanowires exceed 10 µm in length and the height can be varied from 12 to around 40 nm. The nanocrystalline structure of the ZnO wires was confirmed by high-resolution transmission electron microscopy (HRTEM). The electrical conductivity was found to be of the order of several Ω cm at room temperature in two terminal measurements.

A polymer, which by pyrolysis transforms into Al–C–N–(O) ceramics, was synthesized from trimethylamine alane and cyan amide, and its applicability as a sintering additive for Si_3N_4 was investigated. Si_3N_4 powders were mixed with the precursor by treatment with organic slurries of the precursor to induce the homogeneous distribution of the additive. The green-bodies were pretreated in air or NH_3 at 800 °C to control the chemical composition of the additive, through which the densification of Si_3N_4 could be improved. Dense samples with very fine grains (<2 μm) were obtained after sintering at 1600 °C in 0.1 MPa N_2. Besides silicon nitride, submicrometer silicon carbide particles were observed in the samples, indicating that this procedure (i.e., the use of this novel sintering additive) also allows for the fabrication of SiC–Si_3N_4 composites.

Single-walled carbon nanotubes (SWNTs) were incorporated into precursor-derived ceramics made from a polysilazane. To improve the dispersion of the nanotubes in the liquid precursor and finally in the ceramic matrix, the SWNTs were chemically modified by (iodomethyl)trimethylsilane via a radical reaction. The functionalization degree of the modified SWNTs was determined to be 3 atom %. Microscopic investigation combined with viscosity measurements and thixotropy tests demonstrated that the functionalized SWNTs are more homogeneously dispersed in the liquid SWNT/polymer mixtures and the solid cross-linked precursor, as compared to pristine nanotubes. SWNT/Si-C-N ceramics with nanotube contents of up to 1 wt % were obtained through pyrolysis of cross-linked SWNT/polymer composites at 1000 degrees C. The presence of intact nanotubes in these composites could be verified by scanning transmission electron microscopy. The high viscosity of the SWNT/polysilazane mixtures was identified as an important prerequisite for attaining good nanotube dispersion in the Si-C-N matrix.

Indium tin oxide (ITO) has attracted intense interest as the most important transparent conducting oxide (TCO) that sees wide use in many opto‐electronic and photo‐chemical devices. The goal of this study is to explore the possibility of depositing ITO thin films using a bioinspired aqueous deposition route as an alternative. On the surface of sulfonated‐self assembled monolayers, Sn‐doped indium hydroxide films are obtained via a hydrogen peroxide‐assisted method. As a result, the as‐deposited indium tin hydroxide films possess a single hexagonal phase of In(OH)3· xH2O (0 ≤ x ≤ 1) with Sn doping percentage of (1.7 ± 0.2) at % and a column‐like hierachical microstructure. Structural, compositional and property studies, including electron microscopy, X‐ray diffraction, photoelectron spectroscopy, optical transmittance, photoluminescence and four‐probe conductivity measurements, are conducted. The possible mechanism based on oriented attachment is discussed for the film growth. Strong room temperature photoluminescence within the near UV range is observed in the case of Sn‐doped, but not in the one of the pure In(OH)3· xH2O films. Annealing of the indium tin hydroxide films above 200 °C gives nanocrystalline Sn:In2O3 films with higher UV and visible transparency and electrical conductivity compared with those of pure In2O3 films. The influence of annealing atmosphere is investigated.

A composite composed of SiC filler and Si–B–C–N matrix retained its properties even after heat treatment at 2000 °C for 10 h in Ar. The weight loss of the composite was less than 2% at 2100 °C. The composite showed excellent resistance to creep at 1400 °C in air and was strongly oxidation resistant at least up to 1450 °C. The material can be used for the fabrication of fiber-reinforced ceramic matrix composites with high thermal stability.

Abstract Three borazine-modified polycarbosilanes were synthesized by reaction of poly[1,2-ethynediyl-(methylsilylene)], [HSi(Me)C≡C]n, and borazine, B3N3H6 using different stoichiometries. The polymeric precursors were transformed into inorganic Si–B–C–N materials by solid state thermolysis at 1400 °C each in 88% yield. High temperature thermogravimetric analysis in an argon atmosphere showed no substantial decomposition reactions below 1800 °C. Crystallization behavior up to 2000 °C in a nitrogen atmosphere was studied by post-thermolysis heat treatment of as-obtained ceramics at various temperatures and subsequent examination of samples at room temperature using powder X-ray diffraction. Ceramics annealed at 1800 °C were additionally characterized by transmission electron microscopy.

Nanocomposites consisting of precursor-derived Si–C–N ceramics incorporated with carbon nanotubes (CNTs) were successfully prepared by casting of a mixture of CNTs and a liquid precursor polymer followed by cross-linking and thermolysis. The effect of CNTs on the fracture toughness of these nanocomposites was investigated by a thermal loading technique. The results reveal a dependence of the fracture toughness on the type of the CNTs. One type shows a significant increase of the fracture toughness at CNT contents of only 1–2mass%, whereas the other one exhibits no effect. The microstructural effects of CNTs observed at the fracture surfaces of the nanocomposites by scanning electron microscope (SEM) and transmission electron microscope (TEM) can be correlated with the observed fracture toughness behavior.