Possible cage-like nanostructures formed by amino acids

We report possible cage-like nanostructures formed by a representative amino acid, serine octamers and decamers, determined by binding energy calculations and molecular dynamic simulations using the density functional tight-binding method. We used the l-handed serine to construct complex conformers linked by hydrogen bonds. We found the structures linked by -COOH···O=C- to be the most stable conformers and the calculation of the vibrational modes of complexes further illustrated this result. We attempted to apply our cage-like structures to the delivery of C(20) and cycloserine as model molecules. Our results may shed light on the design of cage-like biocompatible complexes for drug delivery.     

多级树状纳米结构聚苯胺的电化学制备

建立一种无模板的恒电位电聚合方法,可在室温下制备对甲基苯磺酸（p-TSA）掺杂的多级树状纳米结构聚苯胺（PANI）.根据电聚合曲线分析了PANI的聚合机理.扫描电镜（SEM）、透射电镜（TEM）观察表明制备的PANI具有均匀的多级树状纳米结构.紫外可见吸收光谱（UV-Vis）和红外光谱（FTIR）则显示所制备的PANI为掺杂态.该电沉积方法具有简便、易操作的特点,还可应用于其他纳米结构导电聚合物的可控制备.     

Constructing magnetic polyaniline/metal hybrid nanostructures using polyaniline/Fe3O4 composite hollow spheres as supports

Polyaniline (PANI)/Fe₃O₄ composite hollow spheres have been successfully synthesized in one step using sulfonated polystyrene (PS) spheres as templates. The magnetic PANI hollow spheres were used as supports for noble metal nanoparticles (NPs) such as Au and Pd. The morphology, composition and magnetic properties of the resulting products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, inductively coupled plasma (ICP) atomic spectra and vibrating sample magnetometer. The catalytic activity of magnetic PANI/Au composite shells on the oxidation of dopamine was investigated by cyclic voltammetry. The obtained results provide our product with a practical application for the detection of dopamine. On the other hand, the catalytic activity of magnetic PANI/Pd composite shells on the reduction of 4-nitroaniline was investigated by spectroscopic methods and compared with Pd/C catalyst which was already widely used in industrial production.     

Water-soluble multiwalled carbon nanotubes functionalized with sulfonated polyaniline

Multiwalled carbon nanotubes (MWNTs) functionalized with a water-soluble conducting polymer, sulfonated polyaniline (SPAN), were prepared by in situ polymerization of aniline followed by sulfonation with chlorosulfonic acid in an inert solvent and by hydrolysis in water. Electron microscopy, laser Raman spectroscopy, X-ray photoelectron spectroscopy, and UV-vis absorption spectroscopy were employed to characterize the morphology and chemical structure of the resulting product. The results show that the quinonoid structure of SPAN preferentially interacts with the nanotubes and is stabilized by strong pi-pi interaction between two components. The structure of MWNTs was not perturbed by the incorporation of SPAN, since the pi-pi interaction between MWNTs and SPAN is much weaker in comparison to that of the carbon covalent bond. The SPAN functionalized MWNTs are highly dispersible in water, thus opening new possibilities for their prospective technological applications.     

Facile synthesis of hydrophobic fluoroalkyl functionalized silsesquioxane nanostructures

New fluorinated polyhedral oligomeric silsesquioxane (F-POSS) structures possessing a high degree of hydrophobicity have been prepared via a facile corner-capping methodology.     

Nano-silicon/polyaniline composite for lithium storage

The nano-silicon connected by a nest-like polyaniline (PANi) was simply synthesized by a chemical polymerization process. The cycle stability and rate performance of the Si/PANi composite were greatly enhanced compared with the pristine nano-silicon. The improved electrochemical characteristics are attributed to the volume buffering effect as well as effective electronic conductivity of the nest-like polyaniline, and lower aggregation of the nano-silicon.     

Conductive composite of polyaniline and tungsten carbide

Conductive polyaniline/tungsten carbide (PANI/TC) composite was synthesized via polymerization of the aniline monomer by (NH₄)₂S₂O₈/H₂SO₄ oxidant system in the presence of an aqueous suspension of TC. The structure, thermal stability and conductivity of PANI/TC composite were studied and the results were also compared with the pure PANI. The results showed that there was a strong interaction between the TC particles and PANI molecular chains. The crystalline structure of TC remained undisturbed upon with interaction with PANI chains. The thermal stability of PANI/TC composite was better than that of pure PANI. The direct current conductivity values of PANI/TC composite decreased slowly as the temperature increased from 25 to 165°C and PANI/TC composite exhibited significantly higher conductivity than the pure PANI.     

Molybdic acid doped polyaniline micro/nanostructures via a self-assembly process

Molybdic acid (H₂MoO₄, MA) doped polyaniline (PANI) micro/nanostructures were prepared by a self-assembly process in the presence of ammonium persulfate ((NH₄)₂S₂O₈, APS) as the oxidant. The morphology of PANI-MA changed from nanofibers or nanotubes (～160 nm in diameter) to co-existence of nanofibers and microspheres (～3 μm in diameter) and that accompanied an enhancement of the conductivity from 5.42 × 10^?3 S cm^?1 to 2.8 × 10^?1 S cm^?1as the molar ratio of MA to aniline varied from 0.01 to 1.5. With increasing the polymerization time, moreover, the pH value of the reaction solution not only decreased due to sulfuric acid produced during the course of the polymerization, but also accompanied a change in morphology from microspheres to nanofibers. All above-mentioned observations could be interpreted by spherical and cylindrical micelle composed of MA as the “soft-template” in forming the micro/nanostructures.     

Trends in polymers functionalized nanostructures for analysis of environmental pollutants

Functional polymers have attached attention in recent years due to their wide applications and unique properties such as sound sensitivity, electrical, catalytic activity, etc for analysis pollutants. The synthesis of functionalized polymers can be affected by several factors, such as the polymerization process, the composition of polymers, and functionalization. However, the scaling-up process from laboratory to industrial is still limited due to its matrix process and steps. We have discussed: i) types of nanostructures and polymer functionalizations, ii) the analytical performance of the functionalized polymers for the analysis of pollutants like toxic gas, pesticide residues, heavy metal, and aromatic compounds, iii) the design and simple concept of the scaling-up process, iv) a parameter affecting the scaling-up process of the synthesis and application of the functionalized polymer nanostructures for the analysis of pollutants. This review will help industry experts and researchers with developing the analysis.     

Nanocomposites based on functionalized nanotubes in polyaniline matrix by plasma polymerization

A co-spraying method of binary mixture aniline–single-walled nanotubes (SWNTs) in a plasma stream is proposed as an alternative to design new composites and nanotube functionalizing. The electrical characterizations, Fourier transform-infrared spectroscopy (FT-IR) and Raman spectra show a chemical bonding to the nanotube surface. I–V characteristics show a combined effect of the conduction mechanisms imposed by space charged limited currents (SLCS) and the metallic/semimetallic character of the nanotubes.     

MnO2/polyaniline hybrid nanostructures on carbon cloth for supercapacitor electrodes

Journal of Solid State Electrochemistry - A facile two-step strategy is developed for synthesis of MnO2/polyaniline (PANI) hybrid nanostructures on carbon cloth (CC). Vertically aligned PANI...     

Well-dispersed multi-walled carbon nanotube/polyaniline composite films

Multi-walled carbon nanotube (MWNT)/polyaniline (PANI) composite films with good uniformity and dispersion were prepared by electrochemical polymerization of aniline containing well-dispersed MWNTs. The results of transmission electron microscopy (TEM) show that aniline can be used to solve MWNTs via formation of donor–acceptor complexes. Scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) revealed that the well arrangement of PANI-coated MWNTs in these films facilitated improved electron and ion transfer relative to pure PANI films and this may be due to the strong interaction between MWNTs and PANI.     

Electromagnetic nanocomposites prepared by cryomilling of polyaniline and Fe nanoparticles

The polyaniline (PANI)/iron nanocomposites have been prepared by high‐energy ball milling under cryogenic temperatures, namely cryomilling, of PANI with Fe nanoparticles. It takes 5 h to refine the Fe into an average grain size of 20 nm and to get homogeneously dispersed in PANI matrix. The obtained PANI/Fe nanocomposites have a maximum conductivity of 0.78 S cm^?1 after 2‐h cryomilling, whereas its coercivity increases monotonously with time in the range of experiment up to 10 h. It is found that the sizes of Fe particles have obvious effects on both electrical and magnetic properties. When compared with micrometer Fe particles as raw materials, Fe nanoparticles result in somewhat lower conductivity but a much higher coercivity exceeding 400 Oe. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1571–1576, 2008     

Electromagnetic functionalized and core-shell micro/nanostructured polypyrrole composites

Core-shell micro/nanostructured and electromagnetic functionalized polypyrrole (PPy) composites were prepared by a self-assembly process associated with the template method in the presence of p-toluenesulfonate acid (p-TSA) as the dopant, in which the spherical hydroxyl iron (Fe[OH], 0.5-5 microm in diameter) functioned not only as the hard template, but also as the "core" of the micro/nanostructure, and the self-assembled PPy-p-TSA nanofibers (20-30 nm in diameter) acted as the "shell" (50-100 nm in thickness) of the microspheres. We found that the core-shell micro/nanostructures exhibit controllable electromagnetic properties by adjusting the mass ratio of Fe[OH] to pyrrole monomer. The micelle model was proposed to interpret the self-assembly of the core-shell micro/nanostructured composites.     

Novel electromagnetic functionalized γ‐Fe2O3/polypyrrole composite nanostructures with high conductivity

In general, the conductivity of polypyrrole (PPy) is reduced by addition of magnetic nanoparticles as the additives owing to insulating effect of magnetic nanoparticles. In this article, novel electromagnetic functionalized PPy composite nanostructures were prepared by a template‐free method associated with γ‐Fe₂O₃ nano‐needles as the hard templates in the presence of p‐toluene‐sulfonic acid (p‐TSA) and FeCl₃·6H₂O as the dopant and oxidant, respectively. It was found that the molar ratio of γ‐Fe₂O₃ to pyrrole monomer represented by [γ‐Fe₂O₃]/[Py] ratio strongly affected the morphology and the conductivity of the γ‐Fe₂O₃/PPy composite nanostructures. A growth mechanism for the composite nanostructures was proposed based on the variance of the morphology with the [γ‐Fe₂O₃]/[Py] ratio. Compared with previously reported γ‐Fe₂O₃/PPy composites, the as‐prepared novel composite nanostructures showed much higher conductivity (up to ～50 times higher). Moreover, the synthesized γ‐Fe₂O₃/PPy composite nanostructures displayed ferromagnetic behavior with a high coercive force. Explanations for these interesting observations were made in terms of the magnetic interaction between ferromagnetic γ‐Fe₂O₃ nano‐needles and spin‐polaron of PPy nanotubes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4446–4453, 2009     

Measuring the unusually slow ionic diffusion in polyaniline via study of yolk-shell nanostructures

We demonstrate a unique capability in partially oxidizing the oligoaniline shell on gold nanoparticles to polyaniline. Because of the solubility difference, the unreacted inner shell section can be selectively dissolved by 2-propanol, giving yolk-shell nanostructures and, thus, making it possible for assessing the oxidized section. The ionic diffusion through the polymer shell is found to be the rate-determining step in the overall process. Conservative estimates show that the diffusion coefficient of AuCl(4)(-) is at least 700 times slower than that of the typical rate values in traditional studies. It is most likely caused by the lack of micropores in the polymer structures. Such mircopores are hard to avoid in preparing polymer membranes by casting or drying of polymers dissolved in organic solvents. We can rule out the presence of irregular pores on the basis of the uniformly oxidized shell section. With the nanoscale shells, the system is sensitive enough to detect minute changes in the shell or small differences among the individual nanoparticles. Even with a small increase in porosity, for example, when the polyaniline shell is swollen using small amounts of DMF (3%, 5%, or 10% in aqueous solutions), the diffusion coefficient of AuCl(4)(-) increases to 4, 11, and 17 times, respectively. Thus, our study demonstrates a new methodology for studying the diffusion of ions in hydrophobic polymers.     

Electrorheological characteristics of polyaniline/titanate composite nanotube suspensions

In this paper, one-dimensional polyaniline/titanate (PANI/TN) composite nanotubes were synthesized by in situ chemical oxidative polymerization directed by block copolymer. These novel nanocomposite particles were used as a dispersed phase in electrorheological (ER) fluids, and the ER properties were investigated under both steady and dynamic shear. It was found that the ER activity of PANI/TN fluids varied with the ratio of aniline to titanate, and the PANI/TN suspensions showed a higher ER effect than that made by sphere-like PANI/TiO₂ nanoparticles. These observations were well interpreted by their dielectric spectra analysis; a larger dielectric loss enhancement and a faster rate of interfacial polarization were responsible for a higher ER activity of nanotubular PANI/TN-based fluids.     

Development of nanostructured polyaniline dispersed smart anticorrosive composite coatings

Modern engineering science and nanotechnology have hastened the development of high performance corrosion‐resistant coatings having a broad spectrum of effectivity under a wider range of hostile environments. The formulation of such coating systems is expected to cause a major revolution in the corrosion world. Conducting polymers have recently proved to be an effective alternative to phosphate–chromate pretreatment that is hazardous due to toxic hexavalent chromium. Moreover, improvements in environmental impact can be achieved by utilizing nanostructured particulates in coating and eliminating the requirement of toxic solvents. The paper reports some preliminary investigations on the corrosion resistance performance of nanostructured methyl orange (MO)‐doped polyaniline (PANI)/castor oil polyurethane (COPU) composite coatings on mild steel (MS). The nanostructure of the MO‐PANI was confirmed by transmission electron microscopy (TEM). The corrosion protective performance was evaluated by physico‐mechanical properties, corrosion rate, and open circuit potential measurements. These coatings were found to act as “corrosion sensors” by exhibiting different colors when placed in acid as well as alkaline media. The protective behavior of coatings was attributed to the formation of a passive iron oxide/dopant layer at the metal‐coating interface that impedes the penetration of the corrosive ions. Copyright © 2008 John Wiley & Sons, Ltd.     

Spectral characteristics of polyaniline nanostructures synthesized by using cyclic voltammetry at different scan rates

The polyaniline nanofibers with different sizes were synthesized by using cyclic voltammetry at different potential scan rates, in the presence of ferrocenesulfonic acid. The potential scan rate controlled the formation and growth of polyaniline nuclei, which plays a key role in controlling nanofiber sizes. The average diameters of nanofibers decreased from about 130 nm to about 80 nm as the potential scan rate increased from 6 to 60 mV s (-1). We first observed an ordered change in the following spectra with the nanofiber sizes of polyaniline. The spectra of the X-ray diffraction indicated that the partially crystalline form existed in the polyaniline nanofibers and that the crystallinity of polyaniline increased with decreasing diameter of polyaniline nanofibers. The ESR spectra revealed the fact that the decrease in the intensity of the ESR signal was accompanied by the increase in the value of the peak-to-peak line width Delta H pp as the diameter of polyaniline nanofibers decreased. The (1)H NMR spectra showed that a peak in a triplet caused by the +/- NH free radical was split into two peaks with different intensities and that their relative intensity also changed with the diameter of the polyaniline nanofibers.     

Relationship between ammonia sensing properties of polyaniline nanostructures and their deposition and synthesis methods

The ammonia absorption properties of polyaniline nanostructures are studied in terms of sensitivity, response and recovery times and stability. These characteristics are obtained by measuring, at room temperature, the absorbance variations at 632 nm. The nanostructures are synthesized either by interfacial or rapid or dropwise polymerizations with the oxidant-to-monomer mole ratio equals to 0.5 or 1. The influence of the deposition method (in-situ or drop-coating technique) as well as the nature of the dopant (HCl, CSA or I₂) on the gas detection properties are also studied. The results show a strong dependence of the morphology on the deposition method, the in-situ technique leads to the best sensitivity and response time. For this deposition method, the nanostructures sensitivity, response time and regeneration rate depend on the synthesis method, the dopant and the mole ratio. The ageing effect after 8 months under ambient conditions and the mechanism of interaction between the polyaniline nanostructures and ammonia molecules are also presented.