Communications
Step-Wise Synthesis of InP/ZnS Core−Shell Quantum Dots and the Role of Zinc Acetate
Euidock Ryu - ,
Sungwoo Kim - ,
Eunjoo Jang - ,
Shinae Jun - ,
Hyosook Jang - ,
Byungki Kim - , and
Sang-Wook Kim
Stabilization and Functionalization of Polymer Multilayers and Capsules via Thiol−Ene Click Chemistry
Luke A. Connal - ,
Cameron R. Kinnane - ,
Alexander N. Zelikin - , and
Frank Caruso
First Discovery of Tetravalent Ti4+ Ion Conduction in a Solid
Naoyoshi Nunotani - ,
Shinji Tamura - , and
Nobuhito Imanaka *
Reviews
Nonhydrolytic Processing of Oxide-Based Materials: Simple Routes to Control Homogeneity, Morphology, and Nanostructure
P. H. Mutin - and
A. Vioux *
Over the past decade, there has been an increasing number of reports on low-temperature preparations of oxides and organic−inorganic hybrids (including sol−gel, solvothermal synthesis, and atomic layer deposition) that take place in nonaqueous media and involve no water as a reactant. This growing interest lies on the ability of these nonhydrolytic routes (in organic solvents, unusual media, condensed phase or under vapor deposition conditions) to reach a higher control over composition, morphology, and structure. An overview of the main results is proposed here, which emphasizes the molecular approach (molecular precursors used, nonhydrolytic reactions involved), the ability to design oxide-based materials with a high degree of homogeneity (mixed oxides, organically modified silicates and ceramics, polysiloxane resins, polymer nanocomposites, etc.) and specific nanostructures (nanoparticles, mesocrystals, nanoporous materials, nanocomposites, nanolayers).
Articles
Dopant−Host Oxide Interaction and Proton Mobility in Gd:BaCeO3
Francesco Giannici *- ,
Alessandro Longo - ,
Antonella Balerna - , and
Antonino Martorana
The local structure of Gd:BaCeO3 at different dopant concentrations (2−20%) was studied by X-ray absorption spectroscopy. The EXAFS analysis shows that the environment of the regular Ba2+ and Ce4+ cations is to a limited extent affected by doping. The local structure of gadolinium shows an expansion of the first coordination shell of oxygens, consistent with the ionic radius of Gd3+, but a contraction of the next neighboring shells of cations. In particular, the Ba2+ second neighbors get closer to the dopant, which can be originated by the effective negative charge sharply localized on the dopant. Comparison between EXAFS data of dry and hydrated compounds confirms this interpretation, showing a strong interaction of Gd3+ with positively charged defects. The environment of gadolinium is compared with the previously investigated local structure of dopants in Y:BaCeO3 and In:BaCeO3. It is observed that yttrium and gadolinium, which induce higher proton conductivity, are characterized by low solubility and strong interaction with positive defects; on the contrary, the lower proton conductivity of In:BaCeO3 coexists with full dopant solubility and insignificant interaction with oxygen vacancies and hydroxyls. A comprehensive interpretation of this behavior is proposed, in terms of a different dopant−host oxide interaction.
Spin-Coated CdS Thin Films for n-Channel Thin Film Transistors
Jong-Baek Seon - ,
Sangyoon Lee - ,
Jong Min Kim *- , and
Hyun-Dam Jeong *
Low-cost and high-performance materials fabricated at low temperatures via solution processes are of great interest in the field of printable and flexible electronics. We have investigated a new solution-based approach to the synthesis of semiconducting chalcogenide films for use in thin-film transistor (TFT) devices in an attempt to develop a simple and robust solution process for the synthesis of inorganic semiconductors. Our material design strategy is to use a sol−gel reaction for the deposition of a spin-coated CdS film that can then be converted to a xerogel material. By carrying out the spin-coating of a L2Cd(S(CO)CH3)2 (L = 3,5-lutidine) precursor, which condenses at low temperatures to form a CdS network, and then hard-baking at 300 °C under atmospheric pressure, microscopically flat films were successfully obtained. To determine the field effect mobilities of the spin-coated CdS films, we constructed TFTs with an inverted structure consisting of Mo gate electrodes and ZrO2 gate dielectrics. These devices exhibited n-channel TFT characteristics with an excellent field-effect mobility (a saturation mobility of ∼48 cm2V−1 s−1) and a low voltage operation (<5 V), indicating that these semiconducting thin film materials can be used in low-cost and high-performance printable electronics.
Silica Hollow Spheres with Ordered and Radially Oriented Amino-Functionalized Mesochannels
Jin-Gui Wang - ,
Feng Li - ,
Hui-Jing Zhou - ,
Ping-Chuan Sun - ,
Da-Tong Ding - , and
Tie-Hong Chen *
Using anionic surfactant as templates, ordered mesoporous silica hollow spheres (MSHSs) with radially oriented mesochannels were synthesized with the aid of ultrasonic irradiation. The product was consisted of intact and dispersed hollow spheres with the diameter mostly in the range of 100−500 nm. The hollow spheres possessed uniform shell with the thickness of 35−40 nm, and the shell with radially oriented mesopores exhibited well-ordered structure as confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. After extraction of the anionic surfactant templates by solvent, silica hollow spheres with ordered and radially oriented amino-functionalized mesochannels were obtained. Moreover, by adjustment of the sonochemical processing time, the shell thickness, mesostructure (hexagonal, radial, or disordered), and shape of the inner cavity (hexagonal or spherical shape) of the hollow spheres could be facilely tuned. The formation process of the radially ordered mesostructure could be attributed to a relatively slow cooperative realignment process of the silica/surfactant hybrid mesophase in this anionic surfactant templating system. The effectiveness of the radially aligned mesopores was validated by a drug (flurbiprofen) release experiment, in which the hollow spheres exhibited relatively high drug storage capacity (>1000 mg g−1) and much faster drug release rate than that of the flakelike mesoporous SBA-15 particles.
Palladium Coordination Biopolymer: A Versatile Access to Highly Porous Dispersed Catalyst for Suzuki Reaction
Ana Primo - ,
Matz Liebel - , and
Françoise Quignard *
This work describes a simple procedure to obtain hybrid materials based on palladium alginate acting as heterogeneous catalysts for the Suzuki carbon−carbon coupling reactions. When reacted with Na2PdCl4, the carboxylate groups of alginate matrix act as chelating agent for Pd cations, which in turn behave as gelling agent of the support. During further steps of preparation, Pd cations spontaneously reduce to metallic species, and metal nanoparticles are obtained, homogeneously and highly dispersed in the biopolymer matrix. CO2 supercritical drying leads to porous materials with surface area between 500 and 700 m2/g. Pure Pd samples show several unsatisfactory properties; mixed Pd, Ca exchanged samples have been therefore considered. These latter materials show high activity for the Suzuki carbon−carbon coupling reactions and the stability of the catalyst allows several reuses with only a slight loss of activity. The intimate contact between host and metal prevents any leaching of active species.
Double Direct Templated Hollow ZnS Microspheres Formed on Chemically Modified Silica Colloids
Dongyeon Son - ,
Alejandro Wolosiuk - , and
Paul V. Braun *
The effect of surface chemistry of SiO2 colloids dispersed in a nonionic surfactant based lyotropic liquid crystal (LLC) on the double direct templating of hollow mesostructured ZnS capsules was investigated. In double direct templating, a LLC templates the mineralization of ZnS on the surface of a colloidal particle. Removal of the colloid results in a periodically mesostructured hollow capsule. After ZnS mineralization and a subsequent etching of the sacrificial SiO2 core, the ZnS mesostructure was imaged using transmission electron microscopy (TEM). The highest quality mesostructure was observed for poly(acrylic acid) (PAA) functionalized colloids, while other surface chemistries, including bare silica, poly(ethylene glycol), amine, and thiol surface chemistries yielded much less favorable results. In the PAA system, the order of the hexagonally arranged 3 nm mesopores in the ZnS shell closely matched that of the lyotropic liquid crystal template. Detailed TEM revealed the presence of regions where the mesopores lay parallel to the colloidal surface and others where they were perpendicularly arranged. We suspect the PAA functionalization favored both the nucleation of ZnS and organization of the LLC template responsible for templating mesostructured ZnS shell around the colloidal particle.
Local Charge Disproportion in a High-Performance Perovskite
Mirko Arnold *- ,
Qiang Xu - ,
Frans D. Tichelaar - , and
Armin Feldhoff
The temperature-dependent local charge disproportion in the (Ba0.5Sr0.5)(Co0.8Fe0.2)O3−δ perovskite-type oxide (denoted as BSCF) was monitored by in situ electron energy-loss spectroscopy applying monochromized electrons in a transmission electron microscope. At elevated temperatures, oxygen is removed from the crystal lattice in these perovskite-type oxides that is due to a reduction of the transition metal sites. To determine the site-specific valence in the BSCF perovskite, we measured the cobalt and iron L-edges and the oxygen K-edge on increasing the temperature from 298 to 1223 K. It was found that the loss of oxygen at elevated temperatures is mainly due to a reduction of the cobalt site compared to the iron site. The understanding of the site specific redox behavior in this material is important in explaining its long-term instability at intermediate temperatures, which has not been elucidated priory this study.
Molecular and Meso- and Macroscopic Properties of Hierarchical Nanocrystalline ZSM-5 Zeolite Prepared by Seed Silanization
D. P. Serrano *- ,
J. Aguado - ,
G. Morales - ,
J. M. Rodríguez - ,
A. Peral - ,
M. Thommes - ,
J. D. Epping - , and
B. F. Chmelka
Surface-passivating silanization of protozeolitic units has been shown to be an effective strategy for the preparation of ZSM-5 nanocrystals, showing a controlled aggregation degree and a hierarchical porosity. ZSM-5 zeolite materials are thus obtained with adjustable and relatively uniform mesoporosities that have a strong influence on resulting macroscopic reaction properties, especially for macromolecular reagents. The mean sizes of the nanounits and, therefore, the textural and accessibility of these materials can be varied by changing the precrystallization conditions and the concentration of the seed-silanization agent. In addition to conventional characterization techniques, solid-state two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy measurements and the application of the NLDFT model to the argon adsorption isotherms have allowed both the local and the mesoscopic compositions, as well as the structures of the hierarchically porous ZSM-5 materials, to be established. The resulting combination of mesopore sizes and exterior-nanocrystal surface properties of the hierarchically structured ZSM-5 zeolites is shown to catalyze reactions that are otherwise limited by steric and/or diffusional limitations, as demonstrated by their enhanced activity for polyethylene cracking.
Controlling the Structure of Arenedisulfonates toward Catalytically Active Materials
Felipe Gándara - ,
Enrique Gutiérrez Puebla - ,
Marta Iglesias - ,
Davide M. Proserpio - ,
Natalia Snejko - , and
M. Ángeles Monge *
By adjusting the solvothermal synthesis conditions, two ytterbium catalytically active MOF (metal organic framework) materials aimed at two different heterogeneous processes have been obtained as pure phases. Yb-LRH belongs to the first family of layered rare-earth hydroxides (LRH). With a 2D structure, highly related to that of the layered doubles hydroxides, Yb-LRHs have cationic inorganic layers with formula [Yb4(OH)10(H2O)4]n2+ and is a very active and selective catalyst in the sulfide oxidation reaction. The second, Yb-RPF-5, is a 3D rare-earth polymeric framework material, with formula [Yb(OH)(2,6-AQDS)(H2O)] (AQDS = anthraquinone-2,6-disulfonate). With lower coordination for the Yb atom and additional acidity from the coordinated ligands, it acts as a good catalyst in hydrodesulfurization (HDS) reactions. Both materials are bifunctional catalysts in redox and acid processes. Structural features of the materials, as well as their catalytic activity and topology, have been studied.
Self-Organized Anodic TiO2 Nanotube Arrays Functionalized by Iron Oxide Nanoparticles
Athanassios I. Kontos - ,
Vlassis Likodimos - ,
Thomas Stergiopoulos - ,
Dimitrios S. Tsoukleris - ,
Polycarpos Falaras *- ,
Ioannis Rabias - ,
George Papavassiliou - ,
Doohun Kim - ,
Julia Kunze - , and
Patrik Schmuki
Surface functionalization of self-organized TiO2 nanotube (NT) arrays produced by electrochemical anodization is implemented by dextrin-coated iron-oxide nanoparticles leading to a composite semiconductor nanostructure. The morphological and structural properties are studied by electron and atomic force microscopy, X-ray diffraction, X-ray photoelectron, and resonance micro-Raman spectroscopies revealing successful deposition of maghemite (γ-Fe2O3) nanoparticles on the nanotube walls. The nanocomposite surface simultaneously exhibits high photocatalytic activity for the degradation of model pollutants under UV irradiation at relatively low loading levels of the γ-Fe2O3 nanoparticles and light-independent wetting properties, as the initially superhydrophilic surface is converted to a moderately hydrophilic substrate, while obtaining an additional functionality through the magnetic field response of the iron-oxide component that shows appreciable magnetization anisotropy. Electrochemical impedance investigation including Mott−Schottky analysis attests to a significant improvement of the interfacial electron-transfer kinetics together with a modification of the surface chemistry for the functionalized TiO2 nanotubes, promoting electron−hole separation through the polyhydroxyl dextrin shell that mediates charge transfer between the constituent semiconductor oxides and validating their improved photocatalytic performance. These composite nanotubular materials offer the opportunity of advanced applications, where the unique photoinduced reactivity, the controlled wetting behavior, and the magnetic field response can be effectively combined.
Fabrication and Dispersion of Gold-Shell-Protected Magnetite Nanoparticles: Systematic Control Using Polyethyleneimine
Ian Y. Goon - ,
Leo M. H. Lai - ,
May Lim - ,
Paul Munroe - ,
J. Justin Gooding - , and
Rose Amal
A detailed study of the aqueous synthesis of composite 50−150 nm magnetite−gold core−shell nanoparticles with the ability to engineer the coverage of gold on the magnetite particle surface is presented. This method utilizes polyethyleneimine for the dual functions of attaching 2 nm gold nanoparticle seeds onto magnetite particles as well as preventing the formation of large aggregates. Saturation of the magnetite surface with gold seeds facilitates the subsequent overlaying of gold to form magnetically responsive core−shell particles, which exhibit surface plasmon resonance. In-depth characterization and quantification of the gold-shell formation process was performed using transmission electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive spectroscopy, and inductively coupled plasma optical emission spectroscopy. Dynamic light scattering studies also showed that PEI coating of synthesized particles served as an excellent barrier against aggregation. The ability of the gold shell to protect the magnetite cores was tested by subjecting the particles to a magnetite-specific dissolution procedure. Elemental analysis of dissolved species revealed that the gold coating of magnetite cores imparts remarkable resistance to iron dissolution. The ability to engineer gold coverage on particle surfaces allows for controlled biofunctionalization, whereas their resistance to dissolution ensures applicability in harsh environments.
Controlling Nanocrystal Density and Location on Carbon Nanotube Templates
Xiaohui Peng - and
Stanislaus S. Wong
We have demonstrated a covalent route toward site-selective synthesis of MWNT−nanoparticle conjugates containing two different types of nanoscale species, i.e., Au nanoparticles and CdSe QDs. We have quantitatively probed the effects of varying oxidation treatments, precursor concentrations, and incubation times in order to rationally affect the spatial coverage and distribution of either Au NPs or semiconducting QDs on the MWNT sidewalls and tips. The degree of nanoparticulate coverage was found to primarily vary with the intensity of the oxidation treatment, though the hydrophobicity of the nanotube as well as the chemical and steric characteristics of the nanocrystals also played a role in determining the ultimate architecture. In general, the stronger the oxidation treatment, the denser the coating of nanoparticles and/or quantum dots on the nanotube surface. In addition, the use of larger concentrations of precursor nanocrystals along with longer incubation times was conducive to the observation of higher nanoparticle densities on our nanotube templates. Interesting charge transfer, electromagnetic enhancement, and energy-transfer behavior between CNTs and the corresponding nanoparticles/quantum dots have been observed and will likely render such conjugates as key components in a range of nanoscale devices important for photocatalytic and solar applications.
Structural Investigations on Hybrid Polymers Suitable as a Nanoparticle Precipitation Environment
Claudia Feldgitscher - ,
Herwig Peterlik - ,
Michael Puchberger - , and
Guido Kickelbick *
Cross-linked hybrid polymer matrices with tunable hydrophilic/hydrophobic areas were prepared from end-group functionalized poly(ethylene oxides) (PEO) and poly(methylhydrido siloxanes) (PMHS) or trimethylsilyl terminated polydimethyl-co-polymethylhydrido siloxanes (PDMS-PMHS). The combination of the different polymer segments resulted in materials with hydrophilic and metal coordinating sections in a hydrophobic matrix. The polymer morphology was investigated with regard to its chemical composition and structural configuration. Besides spectroscopic methods, DSC and swelling tests were performed to study the chain mobility in the polymer matrix. The cross-linked polymers were swellable in methanol, reaching swelling degrees of up to 550%. On the basis of the excellent swelling behavior and the unique metal ion binding ability of the PEO segments, hybrid nanocomposites were prepared infiltrating the matrix with iron ions and forming nanocrystalline oxide particles in the cross-linked network. The resulting materials were analyzed by electron microscopy techniques, XRD, and small-angle X-ray scattering.
Highly Efficient Adsorption of Bulky Dye Molecules in Wastewater on Ordered Mesoporous Carbons
Xin Zhuang - ,
Ying Wan *- ,
Cuimiao Feng - ,
Ying Shen - , and
Dongyuan Zhao
We demonstrate, for the first time, the application of ordered mesoporous carbons with large pore sizes prepared from the surfactant-templating approach in efficient disposal of wastewater containing bulky dye molecules. The adsorption amount for the bulky dye (methylthionine chloride, fuchsin basic, rhodamine B, brilliant yellow, methyl orange, or Sudan G) is almost twice that of the activated carbon in which mesopores contribute almost 100% to the total surface area and volume. The ordered mesoporous carbon adsorbent has a high adsorption rate (>99.9%) for low-concentration dyes, good performance in decoloration regardless of the dye nature, including basic, acidic, or azo dyes, and high stability after dye elution. To establish the relationship between the pore texture and adsorption properties, three kinds of ordered mesoporous carbons with different pore sizes, surface areas, and pore volumes have been synthesized by using phenolic resins as carbon sources and triblock copolymer as a structure-directing agent. The XRD, TEM, and N2 sorption measurements reveal that all mesoporous carbonaceous materials have the highly ordered 2D hexagonal mesostructure, high surface areas (398−2580 m2/g), large pore volumes (0.51−2.16 cm3/g), and uniform pore sizes ranging from 4.5 to 6.4 nm. The adsorption capacities are compared and the pore occupation is estimated to understand the adsorption behaviors in the ordered mesopores with different diameters and models. The spatial effect of dye molecules is the determinative factor for the adsorption in ordered mesoporous carbons with various pore textural properties. The mesoporous carbon with an extremely high surface area (2580 m2/g), a large pore volume (2.16 cm3/g), and bimodal pores (6.4 and 1.7 nm) prepared from the silica−carbon composite shows the highest adsorption capacities for bulky basic dyes among the three ordered mesoporous carbons.
Controlled Synthesis and Water Dispersibility of Hexagonal Phase NaGdF4:Ho3+/Yb3+ Nanoparticles
Rafik Naccache - ,
Fiorenzo Vetrone - ,
Venkataramanan Mahalingam - ,
Louis A. Cuccia - , and
John A. Capobianco *
The luminescence properties of hexagonal sodium gadolinium fluoride nanoparticles co-doped with Ho3+ and Yb3+ (NaGdF4:Ho3+/Yb3+), prepared using a thermal decomposition synthesis route, were evaluated following 980 nm excitation. The synthesized nanoparticles were easily dispersed in nonpolar solvents, showed an extremely narrow particle distribution, and were determined to have a mean diameter of 15.6 ± 1.2 nm. The predominantly green upconversion emission was observed to increase with increasing Ho3+ concentration due to an enhanced energy transfer (ET) from the neighboring Yb3+ ions. Post-synthesis, the nanoparticles were dispersed in water via modification of the capping oleic acid (OA) ligand. Upconversion emission intensity was observed to decrease upon dispersion in aqueous media likely due to an increase in nonradiative decay pathways. A total ligand exchange with poly(acrylic acid) (PAA) resulted in slightly more intense upconversion emission relative to oxidation of the OA to azelaic acid.
Covalent Grafting of Redox-Active Molecules to Vertically Aligned Carbon Nanofiber Arrays via “Click” Chemistry
Elizabeth C. Landis - and
Robert J. Hamers *
Electrochemically active ferrocene groups were covalently linked to vertically aligned carbon nanofibers (VACNFs) in a simple and efficient manner via the Cu(I)-catalyzed azide alkyne cycloaddition (CuAAC), one form of “click” chemistry. The VACNFs were terminated with azide groups followed by the attachment of ethynylferrocene through a 1,4-disubstituted 1,2,3-triazole linkage. Our results show that the CuAAC reaction goes to completion in one hour and provides highly stable attachment of electrochemically active ferrocene groups to the nanofibers. X-ray photoelectron spectroscopy measurements of the density of surface-bound ferrocene molecules are in good agreement with those determined by cyclic voltammetry. The rates of electron transfer were found to be slightly faster than those measured previously through alkyl linkages to the VACNF surface. Stability tests show that the covalently grafted ferrocene groups are stable for more than 1500 repeated cyclic voltammograms and over a potential window of >1.5 V, limited by the solvent. These results suggest that the use of “click” chemistry with VACNFs provides a facile route toward synthesis of high-surface-area electrodes with high stability and tailored electrochemical properties.
Oriented Mesoporous Silica Films Obtained by Electro-Assisted Self-Assembly (EASA)
Aurélie Goux - ,
Mathieu Etienne - ,
Emmanuel Aubert - ,
Claude Lecomte - ,
Jaafar Ghanbaja - , and
Alain Walcarius *
Highly ordered and vertically oriented mesoporous silica films can be generated by electro-assisted self-assembly (EASA). The method involves the electrogeneration of hydroxide ions at an electrode surface immersed in an hydrolyzed sol solution (containing typically tetraethoxysilane, TEOS, and cetyltrimethylammonium bromide, CTAB) in order to catalyze polycondensation of the precursors and self-assembly of hexagonally packed one-dimensional channels that grow perpendicularly to the support. Vertically aligned mesostructures have been demonstrated by TEM imaging and by grazing incidence X-ray diffraction (GIXD), this latter technique enabling characterization of thin films directly on their underlying electrode surface. The influence of the electrosynthesis medium composition (precursor and surfactant concentrations, surfactant chain length) on the mesostructural order and film thickness has been thoroughly examined. It was shown that the highly ordered and oriented mesoporous silica films can be obtained over a wide composition of the starting sol (i.e., 10−200 mM CTAB and 50−350 mM TEOS) and that the lattice parameter can be moderately tuned by changing the chain length of the surfactant template. Thickness of these films can be accurately controlled by applying galvanostatic conditions and by varying the deposition time, which offer the versatility to be applied in the same way to electrodes of different nature without overpotential problems encountered in the potentiostatic mode. Thin mesoporous films are often covered with an additional byproduct made of particulate aggregates arising from bulk gelification at the electrode/solution interface. Getting aggregate-free thin films is possible by working in diluted solutions (i.e., [TEOS] < 125 mM and CTAB/TEOS ratio <0.32) and with a short deposition time (∼10 s). Voltammetric experiments carried out on these films deposited onto planar indium−tin-oxide electrodes, after template extraction, have revealed very sensitive responses to solution-phase redox probes as a result of fast mass transport from the external solution through the film to the electrode surface. Quantitative characterization of these mass transfer processes reveals that apparent diffusion coefficients as high as about 1 × 10−7 cm2 s−1 can be reached but great care should be taken in defining the film synthesis conditions that may lead to some additional limiting effects.
Grafted Functional Polymer Nanostructures Patterned Bottom-Up by Colloidal Lithography and Initiated Chemical Vapor Deposition (iCVD)
Nathan J. Trujillo - ,
Salmaan H. Baxamusa - , and
Karen K. Gleason *
Colloidal lithography, a popular inexpensive alternative to conventional lithography, uses two−dimensional self-assembled monolayer arrays of colloidal nanoparticles as a lithographic template. Combined with initiated chemical vapor deposition (iCVD), which offers unprecedented opportunity for producing grafted polymeric layers, this work demonstrates a generic “bottom-up” process as an inexpensive, simple, and environmentally friendly technique for creating robust well-ordered arrays of functional patterned polymeric nanostructures up to 500 nm in height. These grafted “nanobowl” patterns are produced for a broad material set of functional organic, fluorinated, and silicon containing polymers. These polymers fully retain the organic functionality of their monomeric precursors, are free of wetting defects, and are robustly tethered to the underlying substrate as shown by their ability to withstand aggressive solvent. Furthermore, using this method we pattern a novel low dielectric constant polymer down to 25 nm without the need for environmentally harmful solvents.
Electrical and Thermoelectric Properties of Poly(2,7-Carbazole) Derivatives
Réda Badrou Aïch - ,
Nicolas Blouin - ,
Angélique Bouchard - , and
Mario Leclerc *
A series of alternating poly(2,7-carbazole) derivatives have been synthesized. The evaluation of their thermoelectric properties in doped films revealed high electrical conductivity (up to 500 S/cm) and a relatively high Seebeck coefficient (up to 70 μV/K). The best compromise between these two thermoelectric parameters led to a maximum value of 19 μW m−1 K−2 as the power factor. As observed from X-ray analyses, it has been observed that the high electrical conductivity was obtained with structured polymers. Good air stability was also observed with these thermoelectric polymers.
Preparation of Supramolecular Graft Copolymers and the Subsequent Formation of pH-Sensitive Vesicles
Jian Qian - and
Feipeng Wu
A feasible methodology for the preparation of vesicles through self-assembly of supramolecular graft copolymers (SGPs) was developed. Two types of polymeric vesicles were prepared through self-assembly of two SGPs. For the first SGP, hydrophobic poly(4-vinylpyridine) (PVPy) were used as main chains, and hydrophilic poly(N-vinylpyrrolidone) with carboxylic end groups (PNVP-COOH) were grafted onto the main chains through ionic interaction between the carboxylic groups and pyridine groups. For the second SGP, hydrophobic poly(4-acrylamidobenzoic acid) (PABA) were used as main chains, and poly(N-vinylpyrrolidone) with amino end groups were grafted onto the main chains through ionic interaction between the amino groups and carboxylic groups. Both SGPs could self-assemble to form vesicles in aqueous solution. The size of the vesicles prepared from the PVPy/PNVP-COOH (or PABA/PNVP-NH2) system could be controlled through modulation of the mass ratio of PVPy and PNVP-COOH (or PABA and PNVP-NH2). Both vesicles were sensitive to pH and could be deformed by changing pH. Drug-release studies showed that release rates of the loaded drug (sunset yellow) in the two vesicles could be well-controlled by the pH of the releasing solution.
Single Crystalline Alkaline-Earth Metal Hexaboride One-Dimensional (1D) Nanostructures: Synthesis and Characterization
Syed S. Amin - ,
Shu-you Li - ,
John R. Roth - , and
Terry T. Xu *
Catalytic material-assisted growth of alkaline-earth metal hexaboride (MB6, M = Sr, Ba) 1D nanostructures was achieved by pyrolysis of diborane (B2H6) over alkaline-earth metal oxide (MO) powders at elevated temperature (∼840−870 °C) and low pressure (∼165 mTorr). The as-synthesized MB6 1D nanostructures were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. Results show that the MB6 nanostructures are single crystalline with the preferred growth direction along [001]. The SrB6 nanowires are ∼20−100 nm in diameter and ∼2−5 μm in length. The BaB6 nanostructures have a rectangular cross section (width ∼20−300 nm) and are ∼5−20 μm in length. The growth of these MB6 nanostructures can be attributed to a nontraditional vapor−solid−liquid (VLS)-like growth mechanism. The as-synthesized MB6 1D nanostructures are promising n-type low-dimensional thermoelectric materials.