Conductive poly(3-hexylthiophene) nanofibers and single crystals covered by coily dielectric oligomers and distinctions between their structures developed by self-seeding and isothermal approaches

Fuzzy nanofibers and single crystals developed using poly(3-hexylthiophene) (P3HT)-block-coily oligomers were compared. Based on grazing wide angle X-ray scattering and selected area electron diffraction patterns, grown crystalline structures were mainly edge-on. P3HT fuzzy nanofibers and single crystals were covered by the dielectric coily blocks of polystyrene, poly(methyl methacrylate), and poly(ethylene glycol), leading to brush-like regions on surface of crystals in longitude of P3HT backbones. The atomic force microscopy demonstrated that the single crystals grown by self-seeding method were significantly longer (26–181 µm) and thicker (59 nm–1.4 µm) than the corresponding nanofibers (0.8–21 µm in length and 1.5–23 nm in thickness). P3HT backbones were also more intimately stacked in single crystals in both hexyl side chains and π–π stacking directions, particularly in toluene (13.42–14.63 and 3.30–3.47 ?) than in nanofibers (15.03–16.17 and 3.51–3.67 ?). End coily blocks resulted in slightly higher layer spacings in both nanofibers and single crystals. Shorter P3HT chains were laminated on each other in single crystals; however, they were mostly extended in the nanofibers. Poorer solvents, lower crystallization temperatures, and shorter P3HT chains increased the backbone lamination in single crystals.     

Combustion synthesis as a novel method for production of 1-D SiC nanostructures

1-D nanostructures of cubic phase silicon carbide (beta-SiC) were efficiently produced by combustion synthesis of mixtures containing Si-containing compounds and halocarbons in a calorimetric bomb. The influence of the operating parameters on 1-D SiC formation yield was studied. The heat release, the heating rate, and the chamber pressure increase were monitored during the process. The composition and structural features of the products were characterized by elemental analysis, X-ray diffraction, differential thermal analysis/ thermogravimetric technique, Raman spectroscopy, scanning and transmission electron microscopy, and energy-dispersive X-ray spectrometry. This self-induced growth process can produce SiC nanofibers and nanotubes ca. 20-100 nm in diameter with the aspect ratio higher than 1000. Bulk scale Raman studies showed the product to be comprised of mostly cubic polytype of SiC and that finite size effects are present. We believe that the nucleation mechanism involving radical gaseous species is responsible for 1-D nanostructures growth. The present study has enlarged the family of nanofibers and nanotubes available and offers a possible, new general route to 1-D crystalline materials.     

pH‐Triggered Self‐Assembly of Cellulose Oligomers with Gelatin into a Double‐Network Hydrogel

Multicomponent systems for self‐assembled molecular gels provide huge opportunities to generate collective or new functions that are not inherent in individual single‐component gels. However, gelation tends to require careful and complicated procedures, because, among a myriad of kinetically trapped structures related to the degree of mixing of multiple components over a wide range of scales, from molecular level to macroscopic scale, a limited number of structures that exhibit the desired function need to be constructed. This study presents a simple method for the construction of double‐network (DN) hydrogels with improved stiffness composed of crystalline cellulose oligomers and gelatin. The pH‐triggered self‐assembly of cellulose oligomers leads to the formation of robust networks composed of crystalline nanofibers in the presence of dissolved gelatin, followed by cooling to allow for the formation of soft gelatin networks. The resultant DN hydrogels exhibit improved stiffness; the improvement in gel stiffness with double networking is comparable to that of previously reported DN hydrogels produced via a time‐consuming enzymatic reaction.     

Exploration on the microwave‐assisted synthesis and formation mechanism of polyaniline nanostructures synthesized in different hydrochloric acid concentrations

Under microwave‐assisted synthesis, polyaniline (PANI) products with multiple nanostructures were synthesized by the oxidative polymerization of aniline and ammonium peroxodisulfate in the different concentrations of hydrochloric acid solutions. The structural analysis of PANI using FTIR, UV, and XPS indicated that phenazine‐like oligomers were produced in acid‐free and low acidic systems. Moreover, long linear PANI chains were obtained in the presence of highly acidic solutions. The morphology of PANI observed by SEM and TEM showed that nanoscale structures, including stacked sheets, nanotubes, branched nanofibers, and uniform nanofibers, occurred respectively in acid‐free solution, low acidity, medium and high acidity systems, effectively regulating by acidity. The formation mechanism of PANI nanostructures was explored here. The sheets were formed by the oligomers containing flat phenazine rings that can be stacked together with strong π–π interactions. Furthermore, nanotubes were fabricated by the self‐curling of thin sheets consisted of phenazine‐like oligomers with numerous linear units in the chains. The nanofibers are supposed to form by the linear PANI chains and the secondary growth during aniline polymerization caused the branch formation on the nanofibers. All results indicate that acidity, rather than microwave assistance, is the critical factor that determines the polymerization mechanism and the final nanostructure. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3357–3369     

Variable coordination geometries at the diiron(II) active site of ribonucleotide reductase R2

The R2 subunit of Escherichia coli ribonucleotide reductase contains a dinuclear iron center that generates a catalytically essential stable tyrosyl radical by one electron oxidation of a nearby tyrosine residue. After acquisition of Fe(II) ions by the apo protein, the resulting diiron(II) center reacts with O(2) to initiate formation of the radical. Knowledge of the structure of the reactant diiron(II) form of R2 is a prerequisite for a detailed understanding of the O(2) activation mechanism. Whereas kinetic and spectroscopic studies of the reaction have generally been conducted at pH 7.6 with reactant produced by the addition of Fe(II) ions to the apo protein, the available crystal structures of diferrous R2 have been obtained by chemical or photoreduction of the oxidized diiron(III) protein at pH 5-6. To address this discrepancy, we have generated the diiron(II) states of wildtype R2 (R2-wt), R2-D84E, and R2-D84E/W48F by infusion of Fe(II) ions into crystals of the apo proteins at neutral pH. The structures of diferrous R2-wt and R2-D48E determined from these crystals reveal diiron(II) centers with active site geometries that differ significantly from those observed in either chemically or photoreduced crystals. Structures of R2-wt and R2-D48E/W48F determined at both neutral and low pH are very similar, suggesting that the differences are not due solely to pH effects. The structures of these "ferrous soaked" forms are more consistent with circular dichroism (CD) and magnetic circular dichroism (MCD) spectroscopic data and provide alternate starting points for consideration of possible O(2) activation mechanisms.     

Bulk synthesis of polypyrrole nanofibers by a seeding approach

The morphology of doped polypyrrole.Cl powder changes dramatically from granular to nanofibrillar when a very small amount (1-4 mg) of V2O5 nanofibers are added to a chemical oxidative polymerization of pyrrole in aq 1.0 M HCl using (NH4)2S2O8 as the oxidant. Unlike the polyaniline system, a key synthetic requirement in the polypyrrole system is for the seed template to be "active", i.e., to be capable of independently oxidizing the pyrrole monomer. Thin, strongly adherent films can be obtained on inert surfaces such as glass, plastics, etc., directly from the polymerization mixture without any bulk product isolation steps, significantly simplifying the processing of these nanofibers.     

Putting Electrospun Nanofibers to Work for Biomedical Research

Electrospinning has been exploited for almost one century to process polymers and related materials into nanofibers with controllable compositions, diameters, porosities, and porous structures for a variety of applications. Owing to its high porosity and large surface area, a non‐woven mat of electrospun nanofibers can serve as an ideal scaffold to mimic the extracellular matrix for cell attachment and nutrient transportation. The nanofiber itself can also be functionalized through encapsulation or attachment of bioactive species such as extracellular matrix proteins, enzymes, and growth factors. In addition, the nanofibers can be further assembled into a variety of arrays or architectures by manipulating their alignment, stacking, or folding. All these attributes make electrospinning a powerful tool for generating nanostructured materials for a range of biomedical applications that include controlled release, drug delivery, and tissue engineering.

     

Photoreversible supramolecular polymerisation and hierarchical organization of hydrogen-bonded supramolecular co-polymers composed of diarylethenes and oligothiophenes

Diarylethene 1 equipped with two monotopic melamine hydrogen-bonding sites and oligothiophene-functionalized ditopic cyanurate (OTCA) were mixed in a nonpolar solvent to form AA-BB-type supramolecular co-polymers (SCPs) bearing photoswitchable moieties in their main chains and extended π systems as side chains. UV/Vis, fluorescence, dynamic light scattering (DLS), TEM, and AFM studies revealed that the two functional co-monomers formed flexible quasi-one-dimensional SCPs in solution that hierarchically self-organized into helical nanofibers through H-aggregation of the oligothiophene side chains. Upon irradiating the SCPs with UV light, a transition occurred from the H-aggregated state to non-aggregated monomeric oligothiophene side chains, as shown by spectroscopic studies, which indicates the formation of small oligomeric species held together only by hydrogen-bonding interactions. TEM and AFM visualized unfolded fibrils corresponding to elongated single SCP chains formed upon removal of solvent. The helical nanofibers were regenerated upon irradiating the UV-irradiated solution with visible light. These results demonstrated that the supramolecular polymerisation followed by hierarchical organization can be effectively controlled by proper supramolecular designs using diarylethenes and π-conjugated oligomers.     

Electrospun antimony doped tin oxide (ATO) nanofibers as a versatile conducting matrix

Nanoparticles of ATO (antimony doped tin oxide) were used to produce thick conductive, free standing mats of nanofibers via electrospinning. These fibrous mats were incorporated into polymer films to produce a transparent conducting polymer foil. Moreover, the fiber mats can serve as porous electrodes for electrodeposition of Prussian Blue and TiO(2) and were tested in dye-sensitized solar cells.     

Fabrication of one-dimensional colloidal assemblies from electrospun nanofibers

Electrospun nanofibers were used as confining geometries for fabricating 1-D colloidal assemblies. Silica particles dispersed in several different polymer solutions were cast into nanofibers by an electrospinning process. The silica particle configurations were examined in terms of the size ratio of silica particles to nanofibers and the properties of the dispersing medium. As the electrospun fiber was extended highly, the silica particles dispersed in the polymer solution began to assemble spontaneously into a pearl-necklace structure. We also demonstrated the alignment of 1-D silica assemblies using a designed configuration of collector electrodes.     

Polyaniline nanofibers by surfactant‐assisted dilute polymerization for supercapacitor applications

Polyaniline nanofibers doped with citric acid was prepared by a novel surfactant‐assisted dilute polymerization technique. It was possible to synthesize polyaniline nanofibers without using any organic solvent by easier pathway. Polyaniline salt was characterized by conductivity, FTIR, and X‐ray diffraction studies. The specific capacitance behavior of the polyaniline nanofibers was characterized using cyclic voltammetry which exhibits highest specific capacitance of 298 F g^?1. The morphology of the obtained nanofibers was characterized by SEM studies. So, these kinds of specific properties of polyaniline nanofibers could be beneficial to the development of energy storage devices. Copyright © 2008 John Wiley & Sons, Ltd.     

Oligomer-assisted synthesis of chiral polyaniline nanofibers

We report here a novel approach to synthesize chiral PANI nanofibers in an aqueous solution. This new approach requires the following conditions: (1) Polymerization was carried out in concentrated camphor sulfonic acid solutions. (2) Aniline oligomers were used to accelerate the polymerization reaction. (3) Ammonium persulfate (oxidant) was added incrementally to the aniline solution. The high anisotropy factor of these PANI nanofibers is likely due to the "autocatalytic effect" resulting from lower oxidation potentials of aniline oligomers. Our chemical synthesis of the chiral PANI nanofibers is enantioselective and, under the optimized conditions, has an anisotropy factor (g = Deltaepsilon/epsilon) of 2.3 x 10-2.     

Growth of Sr6Rh5O15 single crystals from high-temperature solutions: structure determination using the traditional 3-D and the 4-D superspace group methods and magnetic measurements on oriented single crystals

Single crystals of Sr6Rh5O15 were grown from a molten potassium carbonate flux. The structure was solved by both the traditional 3-D crystallographic approach and the 4-D superspace group approach using JANA2000. Both methods produced an equivalent structure determination, thereby confirming the 4-D superspace group approach as an effective structure solution method for 3-D commensurate composite structures. Sr6Rh5O15 corresponds to the n = 1, m = 1 member of the A3n+3mA'nB3m+nO9m+6n family of 2H hexagonal perovskite-related oxides. This compound is characterized by pseudo-one-dimensional polyhedral chains of four face-sharing RhO6 octahedra followed by one RhO6 trigonal prism. These chains in turn are separated by [Sr](infinity) chains. Magnetic measurements were carried out on oriented single crystals, and a very large magnetic anisotropy in the magnetic susceptibility was observed.     

Engineered hyperstructures based on attaching macromers onto polymers

The combination of polymers with macromers derived from inorganic species and oligomers to yield controlled hyperstructures can potentially allow the design of materials with tunable mechanical, optoelectronic properties and chemical behavior. In this work, novel hybrid structures were processed based upon the controlled insertion of macromers derived from inorganic groups and oligomers into previously chemically modified polymer frameworks. The chemical procedure involved a series of steps that started with the creation of a functionalized framework to act as host for the construction of the polymer-macromer hyperstructures. The designed polymer framework was obtained by incorporating highly polar groups, such as sulfonic acid, into poly(aryl ether sulfones). Following this step, the newly promoted reactive sites were used to insert alkoxysilane groups through reacting modified poly(aryl ether sulfones) with specifically selected silane compounds. The chemical reactions and the obtained novel structures were characterized using NMR, FTIR, AFM and thermal analysis. Results showed that structural parameters such as the concentration of siloxane bonds across the material and the density of cross-links could be controlled by selecting different conditions of reaction. Completely homogeneous and also heterogeneous, but still controlled, structures could be produced using the described procedure. The developed polymer structures containing controlled profiles of concentration, densities and chemical functionalities can have tailorable mechanical properties and chemical activity.     

Control of the morphogenesis of barium chromate by using double-hydrophilic block copolymers (DHBCs) as crystal growth modifiers

A systematic morphosynthesis of barium chromate particles has been performed by using double-hydrophilic block copolymers (DHBCs), which consist of a hydrophilic solvating block and a hydrophilic binding block, as crystal growth modifiers to direct the controlled precipitation of barium chromate from aqueous solution. Several kinds of DHBCs with different functional groups -COOH, -PO3H2, -SO3H, -SH as well as PEG-poly(aminoamine) block-dendrimer copolymers were explored for crystallization and morphology control of barium chromate. Well-defined morphologies of BaCrO4 particles can be produced, such as more or less dendritic X-shaped, elongated X-shaped, or rodlike particles, flower-like plates, ellipsoids, spheres, nanofiber bundles, nanofibers, and other more complex morphologies. In the presence of the phosphonated copolymer PEG-b-PMAA-PO3H2 (degree of phosphonation: 21%) at pH 5, large conelike bundles of nanofibers ranging from 10 to 20 nm in diameter with lengths up to 150 microns can be produced at room temperature, whereas replacement of the covalently bound phosphonate groups by the ionic salt analogue dopant fails to produce this structure, indicating the importance of the functional polymer block structures. The time-resolved formation process of the bundles of nanofibres was investigated, showing a remarkable self-similarity. At temperatures higher than 50 degrees C, in plastic flasks or when undergoing continuous stirring, only ellipsoids or nearly spherical particles can be obtained. This shows that the fiber formation relies on heterogeneous nucleation and is in agreement with a recently published mechanism where fiber formation is due to the vectorially directed self-assembly of primary particles. Our results demonstrate that the integration of DHBCs, taking advantage of the experimental conditions such as crystallization sites, temperature, pH, and reactant concentration, will extend the possibilities for controlling the shape, size, and microstructures of the inorganic crystals by means of a simple mineralization process.     

铜掺杂氧化锌纳米纤维宽线性响应乙醇气体传感器

采用电纺丝技术结合高温煅烧制备了铜掺杂氧化锌复合纳米纤维,并通过XRD,XPS,SEM和TEM等手段对材料进行表征.将所得材料作为敏感层构筑了气体传感器,器件对乙醇蒸气具有很好的传感特性,特别是当Cu/Zn摩尔比为1∶60时,由于Cu组分的活化作用,所得传感器不仅具有高灵敏度、快速响应恢复(2 s/7 s)特性及优良的稳定性,而且在5~104μg/g超大乙醇蒸气浓度范围内都能保持良好的线性关系(R2=0.99),这不仅有利于乙醇实际检测,而且对宽响应范围及高灵敏传感器的发展具有重要意义.     

Assembly of tobacco mosaic virus into fibrous and macroscopic bundled arrays mediated by surface aniline polymerization

One-dimensional (1D) polyaniline/tobacco mosaic virus (TMV) composite nanofibers and macroscopic bundles of such fibers were generated via a self-assembly process of TMV assisted by in-situ polymerization of polyaniline on the surface of TMV. At near-neutral reaction pH, branched polyaniline formed on the surface of TMV preventing lateral association. Therefore, long 1D nanofibers were observed with high aspect ratios and excellent processibility. At a lower pH, transmission electron microscopy (TEM) analysis revealed that initially long nanofibers were formed which resulted in bundled structures upon long-time reaction, presumably mediated by the hydrophobic interaction because of the polyaniline on the surface of TMV. In-situ time-resolved small-angle X-ray scattering study of TMV at different reaction conditions supported this mechanism. This novel strategy to assemble TMV into 1D and 3D supramolecular composites could be utilized in the fabrication of advanced materials for potential applications including electronics, optics, sensing, and biomedical engineering.     

Fabrication of poly(ϵ-caprolactone)/paclitaxel (core)/chitosan/zein/multi-walled carbon nanotubes/doxorubicin (shell) nanofibers against MCF-7 breast cancer

In the present study, paclitaxel (PTX), multi-walled carbon nanotubes (MWCNTs), and doxorubicin (DOX) have been simultaneously doped into the poly(ϵ-caprolactone) (PCL)/chitosan/zein core-shell nanofibers to increase its cytotoxicity for MCF-7 breast cancers killing. The physico-chemical properties of synthesized nanofibers were determined by scanning electron microscope, Fourier-transform infrared spectroscopy, tensile strength, and degradation rate determinations. The in vitro release studies demonstrated the sustained release of drugs from core-shell nanofibrous scaffold. The cytotoxicity and compatibility of core-shell nanofibers were investigated by their treating with MCF-7 breast cancer cells and L929 normal cells, respectively. PCL/PTX/chitosan/zein/MWCNTs/DOX core-shell nanofibers containing 1 wt% MWCNTs, 100 μg ml⁻¹ DOX and 100 μg ml⁻¹ PTX had a high biocompatibility with a 84% MCF-7 cancer cells killing. The in vivo studies revealed the synergic effects of MWCNTs and anticancer drugs on the tumor inhibition. This method could be considered as a new way for developing of MWCNTs loaded-nanofibers for cancer treatment in future.     

Physical properties of TEMPO-oxidized bacterial cellulose nanofibers on the skin surface

Water-dispersed bacterial cellulose nanofibers were prepared via an oxidation reaction using 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (TEMPO) as a catalyst. It was found that TEMPO-oxidized bacterial cellulose nanofibers (TOCNs) synthesized via sodium bromide-free methods are similar to those synthesized using sodium bromide. The TOCNs retained their unique structure in water as well as in emulsion. TOCNs adhere to the skin surface while maintaining nanofibrous structures, providing inherent functions of bacterial cellulose, such as high tensile strength, high water-holding capacity, and blockage of harmful substances. When gelatin gels as model skin were coated with TOCNs, the hardness representing the elasticity was increased by 20% compared to untreated gelatin gel because TOCNs could tightly hold the gelatin structure. When porcine skin was treated with TOCNs, carboxymethyl cellulose, and hydroxyethyl cellulose, the initial water contact angles were 26.5°, 76.5°, and 64.1°, respectively. The contact angle of TOCNs dramatically decreased over time as water penetrated the fibrous structure of the TOCN film. When observed by scanning electron microscopy and confocal microscopy, TOCNs on the skin surface provided physical gaps between particles and the skin, blocking the adsorption of particulate matter to the skin surface. On the contrary, the structure of water-soluble polymers was disrupted by an external environment, such as water, so that particulate matter directly attached to the skin surface. Characterization of TOCNs on the skin surface offered insight into the function of nanofibers on the skin, which is important for their applications with respect to the skin and biomedical research.     

Aggregation and columnar assembly of crescent oligoamides

The aggregation and assembly of crescent oligoamides with two to six benzene residues are investigated. In chloroform, the pentamer and hexamer are found to associate into large aggregates. In the solid state, all oligomers examined associate into columnar assemblies via stacking interactions, as shown by X-ray diffraction data from single crystals and powder samples. The columnar assemblies of the pentamer and hexamer should contain hydrophilic channels defined by the constituent oligomers.