New amphiphilic terphenyl liquid crystals for the preparation of highly ordered ultrathin films

Four new amphiphilic liquid crystals have been synthesized, in which terphenyl was used as the mesogenic unit. In order to enable the formation of Langmuir Monolayers at the air/water-interface, the molecules were equipped with slightly polar headgroups such as esters or a carboxylic acid group. All compounds can be transferred onto solid substrates. In addition, it is possible to prepare freely suspended films of at least one compound in the temperature range of the smectic phases. The phases of the different states, bulk, monolayer, freely suspended film, and Langmuir-Blodgett multilayers have been investigated by means of monolayer isotherms, optical textures, differential scanning calorimetry (DSC) and small angle X-ray scattering.     

Assembling of amphiphilic highly branched molecules in supramolecular nanofibers

We found that the amplification of weak multiple interactions between numerous peripheral branches of irregular, flexible, polydisperse, and highly branched molecules can facilitate their self-assembly into nanofibrillar micellar structures at solid surfaces and the formation of perfect long microfibers in the course of crystallization from solution. The core-shell architecture of the amphiphilic dendritic molecules provides exceptional stability of one-dimensional nanofibrillar structures. The critical condition for the formation of the nanofibrillar structures is the presence of both alkyl tails in the outer shell and amine groups in the core/inner shell. The multiple intermolecular hydrogen bonding and polar interactions between flexible cores stabilize these nanofibers and make them robust albeit flexible. This example demonstrates that one-dimensional supramolecular assembling at different spatial scales (both nanofibers and microfibers) can be achieved without a tedious, multistep synthesis of shape-persistent molecules.     

Synthesis and characterization of highly ordered Ni-MCM-41 mesoporous molecular sieves

Highly ordered Ni-MCM-41 samples with nearly atomically dispersed nickel ions were prepared reproducibly and characterized. Similar to the Co-MCM-41 samples, the pore diameter and porosity can be precisely controlled by changing the synthesis surfactant chain length. Nickel was incorporated by isomorphous substitution of silicon in the MCM-41 silica framework, which makes the Ni-MCM-41 a physically stable catalyst in harsh reaction conditions such as CO disproportionation to single wall carbon nanotubes or CO2 methanation. X-ray absorption spectroscopy results indicate that the overall local environment of nickel in Ni-MCM-41 was a tetrahedral or distorted tetrahedral coordination with surrounding oxygen anions. Hydrogen TPR revealed that our Ni-MCM-41 samples have high stability against reduction; however, compared to Co-MCM-41, the Ni-MCM-41 has a lower reduction temperature, and both the H2-TPR and in situ XANES TPR reveal that the reducibility of nickel is not clearly correlated with the pore radius of curvature, as in the case of Co-MCM-41. This is probably a result of nickel being thermodynamically more easily reduced than cobalt. The stability of the structural order of Ni-MCM-41 has been investigated under SWNT synthesis and CO2 methanation reaction conditions as both require catalyst exposure to reducing environments leading to formation of metallic Ni clusters. Nitrogen physisorption and XRD results show that structural order was maintained under both SWNT synthesis and CO2 methanation reaction conditions. EXAFS results demonstrate that the nickel particle size can be controlled by different prereduction temperatures but not by the pore radius of curvature as in the case of Co-MCM-41.     

Copolypeptide-doped polyaniline nanofibers for electrochemical detection of ultratrace trinitrotoluene

This paper demonstrates a new electrochemical method for the detection of ultratrace amount of 2,4,6-trinitrotoluene (TNT) with synthetic copolypeptide-doped polyaniline nanofibers. The copolypeptide, comprising of glutamic acid (Glu) and lysine (Lys) units, is in situ doped into polyaniline through the protonation of the imine nitrogen atoms of polyaniline by the free carboxylic groups of Glu segments, resulting in the formation of polyaniline nanofibers of emeraldine salt. The free amino groups of Lys segments at the surface of nanofibers provide the receptor sites of TNT through the formation of charge-transfer complex between the electron-rich amino groups and the electron-deficient aromatic rings. Adsorptive stripping voltammetry results demonstrate that the poly(Glu-Lys)-doped nanofibers confined onto glassy carbon electrodes exhibit a remarkable enriching effect and thus sensitive electrochemical response to TNT with a linear dynamic range of 0.5-10 μM and a detection limit down to 100 nM. Moreover, other kinds of nitro compounds show different redox behaviors from TNT at the doped nanofibers, and thus do not interfere with the electrochemical detection of TNT. This study essentially offers a new and simple method for electrochemical detection of ultratrace TNT.     

Palladium nanostructures and nanoparticles from molecular precursors on highly ordered pyrolytic graphite

Nanostructures and nanoparticles of palladium assembled on highly ordered pyrolytic graphite (HOPG) by the adsorption of palladium molecular precursors (MPs), in dichloromethane solutions, have been prepared. Self-assemblies of palladium nanostructures on HOPG were characterized by scanning electron microscopy (SEM), Auger electron spectroscopy (AES), transmission electron microscopy (TEM), and atomic force microscopy (AFM) techniques. In this work, palladium rings had a wide variety of sizes in the nanometer range, and the ring/tube structures were preserved after a reductive process in which palladium metallic nanoparticles were formed. Noncircular structures were observed at HOPG defects and atomic step sites, as well. It is proposed that the observed ring formation of the palladium molecular precursors on HOPG substrates is related to the functional groups in the MPs, van der Waals interactions between particles and between particle-substrate, as well as the wetting properties of the solvent. In the present work, we illustrate several examples of the formation and characterization of palladium complex tubes and the resulting palladium rings, via the reduction process.     

Biofunctionalized dendritic polyaniline nanofibers for sensitive electrochemical immunoassay of biomarkers

Multi-armed dendritic polyaniline nanofibers (MPANFs) were first synthesized and functionalized with horseradish peroxidase (HRP) and carcinoembryonic antibody (anti-CEA) for highly efficient electrochemical immunoassay of carcinoembryonic antigen (CEA, as a model analyte here) in this work. Transmission electron microscope (TEM) and scanning electron microscope (SEM) techniques were employed to characterize the synthesized MPANFs. By using anti-CEA-conjugated core-shell gold-Fe(3)O(4) nanocomposites (GoldMag) as immunosensing probes and biofunctionalized MPANFs as molecular tags, a new sandwich-type homogeneous immunoassay strategy was developed for the determination of CEA by coupling with a home-made flow-through magneto-controlled microfluidic device. Under optimal conditions, the electrochemical immunoassay exhibited a wide dynamic range of four orders of magnitude from 1.0 pg mL(-1) to 50 ng mL(-1) with a low detection limit of 0.1 pg mL(-1) CEA at 3σ. Intra- and inter-assay coefficients of variation were below 10%. The assayed results for clinical serum specimens with the electrochemical immunoassay were received in good accordance with the results obtained from the referenced enzyme-linked immunosorbent assay (ELISA) method.     

Enantioselective recognition by a highly ordered porphyrin-assembly on a chiral molecular gel

Enantioselective recognition of amino acids was achieved by using a highly ordered chiral assembly of achiral porphyrin on a chiral molecular gel. Exceptionally high enantioselectivity was observed for histidine derivatives by monitoring the CD patterns and fluorescence quenching, K(SV) (l): 26.3 × 10(3) M(-1); K(SV)(D)-enantiomer: 7.03 × 10(3) M(-1).     

聚苯胺纳米纤维的共溶剂界面聚合及储能性能研究

本文采用以盐酸溶液为水相、四氯化碳为有机相的界面聚合法,通过向水相中分别引入具有非对称结构的甲醇和乙醇,以及具有对称结构的异丙醇和丙三醇作为共溶剂,成功制备出聚苯胺纳米纤维.采用场发射扫描电镜、紫外可见光谱和傅里叶红外光谱对其形貌和结构进行了表征分析,并通过循环伏安测试、恒流充放电测试和交流阻抗测试着重研究了不同共溶剂...     

Mechanism-based molecular design of highly selective fluorescence probes for nitrative stress

Nitrative stress is implicated in various pathogenic processes, including neurodegenerative disorders, but there is no practical fluorescence probe which can monitor the generation of nitrative stress with high selectivity. To design a suitable fluorescence probe, we have first focused on the fluorescence quenching mechanism of the nitro group, which has been believed to be a unique quencher of fluorescent dyes. We found that nitro group-based fluorescence quenching could be explained in terms of an electron transfer process, from the excited fluorophore to the electron-deficient aromatic nitro moiety. By utilizing this result, we succeeded in developing novel fluorogenic probes, NiSPYs, which can selectively monitor the generation of nitrative stress based on aromatic nitration. NiSPYs showed strong fluorescence enhancement upon the reaction with nitrating agents, including peroxynitrite, but showed little or no fluorescence augmentation in the presence of other reactive oxygen species. NiSPYs should be potentially useful as tools to study the role of nitrative stress in various biological applications.     

Composites of polyaniline nanofibers and molecularly imprinted polymers for recognition of nitroaromatic compounds

This paper reports a monomer strategy for imprinting of 1,3-dinitrobenzene (DNB) molecules at the surface of conductive functional polyaniline nanofibers (PANI) for the first time. It has been demonstrated that the vinyl functional monomer layer on the PANI surface can not only direct the selective occurrence of imprinting polymerization, but can also drive DNB templates into the polymer through charge-transfer complexing interactions between DNB and functionalized PANI. These two basic processes lead to the formation of DNB-imprinted polymers at the surface of polyaniline nanofibers. The capacity to uptake DNB shows that selectivity coefficient in the nanofibers polymers is nearly three times as high as that of traditional imprinted materials and the nanofibers polymers also possess high selectivity toward DNB in comparison to similar nitroaromatic compounds. A linear response of DNB concentration between 2.20×10(-8) and 3.08×10(-6) M was exhibited with a detection limit of 7.33×10(-9) M (S/N=3). These results reported here could form the basis of a new strategy for preparing various polymer-coating layers on polyaniline supports and the molecular imprinting techniques discussed could also find applications in the fields of separation, trace detection, and environmental monitoring.     

Thermal reduction of Pd molecular cluster precursors at highly ordered pyrolytic graphite surfaces

Highly ordered pyrolytic graphite (HOPG) surfaces were modified by the adsorption of Pd molecular precursors from solution. Two palladium-containing molecular precursors were studied, a mononuclear one and a trinuclear one, to compare their affinities and distributions at substrate surfaces. To obtain Pd nanoparticles, these neutral molecular precursors were reduced under a hydrogen atmosphere. Thermogravimetric analysis was carried out to establish the behavior of these precursors at various temperatures. Understanding the thermal stability of these compounds is very important to establish the appropriate conditions to form metallic Pd. The modified surface has been characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy; also, the reductive process was monitored by XPS. Remarkable differences were observed between the mononuclear and trinuclear compounds in terms of dispersion, particle size, and homogeneity. The preference of the trinuclear compound was to deposit at HOPG defects, in contrast to that of the mononuclear one, which was agglomeration on all surfaces. After the application of this technique, not only Pd nanoparticles but also Pd nanowires were obtained.     

Structural and vibrational characterization of polyaniline nanofibers prepared from interfacial polymerization

This work deals with the structural and vibrational characterization of PANI nanofibers prepared through interfacial polymerization using different concentrations of HCl aqueous solution. The results were compared to those obtained by PANI prepared through the conventional route. X-ray diffraction and small-angle X-ray scattering techniques showed that high concentrations of HCl solutions used in the preparation of the PANI nanofibers reduce their crystallinity. The increase of regions with granular morphology was also observed in the scanning electron microscopy images. The changes in the resonance Raman spectra from 200 to 500 cm (-1), FTIR spectra, and the EPR data of the PANI nanofibers reveal an increase in the torsion angles of C ring-N-C ring segments owing the formation of bipolarons in the PANI backbone higher than the PANI samples prepared by conventional route.     

Synthesis and characterization of conductive polyaniline/TiO2 composite nanofibers

Fibrillar conductive polyaniline/TiO₂ (PANI/TiO₂) nanocomposites with different TiO₂ amount were synthesized with a template-free in situ polymerization method and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and conductivity measurement. The morphology determination shows that the PANI/TiO₂ composite nanofibers are relatively uniform with the diameter and length in the range of 20–40 nm and 390–420 nm respectively. It also shows that the TiO₂ of the composite is rutile crystalline and PANI has some degree of crystallinity. The IR measurement indicates that there is a strong interaction between the PANI and TiO₂ nanoparticles, and it has a beneficial effect on the thermal stability of the composite nanofiber. The conductivity of PANI/TiO₂ composites changes with TiO₂ amount and reaches an optimum value of 2.86 S/cm at 11.1 wt% TiO₂. Translated from Journal of Northwest Normal University (Natural Science), 2006, 42(4): 67–70 (in Chinese)     

Preparation of highly conductive, self-assembled gold/polyaniline nanocables and polyaniline nanotubes

One-dimensional gold/polyaniline (Au/PANI-CSA) coaxial nanocables with an average diameter of 50-60 nm and lengths of more than 1 mum were successfully synthesized by reacting aniline monomer with chlorauric acid (HAuCl(4)) through a self-assembly process in the presence of D-camphor-10-sulfonic acid (CSA), which acts as both a dopant and surfactant. It was found that the formation probability and the size of the Au/PANI-CSA nanocables depends on the molar ratio of aniline to HAuCl(4) and the concentration of CSA, respectively. A synergistic growth mechanism was proposed to interpret the formation of the Au/PANI-CSA nanocables. The directly measured conductivity of a single gold/polyaniline nanocable was found to be high (approximately 77.2 S cm(-1)). Hollow PANI-CSA nanotubes, with an average diameter of 50-60 nm, were also obtained successfully by dissolving the Au nanowire core of the Au/PANI-CSA nanocables.     

A renewable bamboo carbon/polyaniline composite for a high-performance supercapacitor electrode material

A high-performance conducting polymer-activated carbon composite electrode material was prepared by potentiostatic deposition of aniline on a hierarchically porous carbon, which was carbonized from the natural bamboo. The obtained composite combined the contribution of the unique properties of the activated carbon and pseudocapacitance of the deposited polyaniline layer. This active material possessed excellent rate capability and good cycle performance, over 92% of the original capacitance is retained after 1,000 cycles. The energy density of the composite can reach 47.5 W h kg⁻¹ calculated only by active mass. It can be a good candidate for high-performance supercapacitor.     

Post-self-assembly cross-linking of molecular nanofibers for oscillatory hydrogels

After a polymerizable hydrogelator self-assembles in water to form molecular nanofibers, post-self-assembly cross-linking allows the catalyst of the Belousov-Zhabotinsky (BZ) reaction to be attached to the nanofibers, resulting in a hydrogel that exhibits concentration oscillations, spiral waves, and concentric waves. In addition to the first report of the observation of BZ spiral waves in a hydrogel that covalently integrates the catalyst, we suggest a new approach to developing active soft materials as chemical oscillators and for exploring the correlation between molecular structure and far-from-equilibrium dynamics.     

A highly thermal-resistant electrospun-based polyetherimide nanofibers coating for solid-phase microextraction

A high-temperature-resistant solid-phase microextraction (SPME) fiber was prepared based on polyetherimide (PEI) by the electrospinning method. The PEI polymeric solution was converted to nanofibers using high voltages and directly coated on a stainless steel SPME needle. The scanning electron microscopy images of PEI coating showed fibers with diameter range of 500–650 nm with a homogeneous and smooth surface morphology. The SPME nanofibers coating was optimized for PEI percentage, electrospinning voltage, and time. The extraction efficiency of the coating was investigated for headspace SPME of some environmentally important polycyclic aromatic hydrocarbons from aqueous samples followed by gas chromatography–mass spectrometry measurement. In addition, the important extraction parameters including extraction temperature, extraction time, ionic strength, as well as desorption temperature and time were investigated and optimized. The detection limits of the method under optimized conditions ranged from 1 to 5 ng L^?1 using time-scheduled selected ion monitoring mode. The relative standard deviations of the method were between 1.1 and 7.1 %, at a concentration level of 500 ng L^?1. The calibration curves of polycyclic aromatic hydrocarbons showed linearity in the range of 5–1000 ng L^?1. The developed method was successfully applied to real water samples and the relative recovery percentages obtained from the spiked water samples were from 84 to 98 % for all the selected analytes except for acenaphthene which was from 75 to 106 %.     

Fabrication of 3D ordered needle-like polyaniline@hollow carbon nanofibers composites for flexible supercapacitors

Carbon nanofiber-based supercapacitors have broad prospects in powering wearable electronics owing to their high specific capacity,fast charge/discharge process,along with long-cycling life.Herein,a poly(ac rylo n it rile-co-β-methyl hydrogen itaconate) copolymer was prepared and used to synthesize flexible hollow carbon nanofibers(HCNFs) via an electrospinning method without breaking after multiple bending.Subsequently,the inner and outer surfaces of HCNFs were evenly covered with ordered needlelike polyaniline(PANI) through in-situ polymerization methods to obtain three-dimensional flexible HCNFs/PANI composites,which exhibited a high capacity 1196.7 F/g at 1 A/g and good cycling stability(90.1% retention at 5 A/g after 3000 cycles).The symmetrical supercapacitor based on the HCNFs/PANI composites also delive red an outsta nding electrochemical performance with high energy/power density(60.28 Wh/kg at 1000 W/kg) and superior cycling durability(90% capacitance retention after at 5 A/g3000 cycles),which confirmed that the HCNFs/PANI composites had a wide application potential in flexible energy storage devices.