Inside Front Cover: Conducting‐Polymer Nanotubes for Controlled Drug Release (Adv. Mater. 4/2006)

Martin and co‐workers report on p. 405 that nanotubes formed from the conducting polymer poly(3,4‐ethylenedioxythiophene) (PEDOT), as shown on the inside cover, can be used for the controlled release of anti‐inflammatory drugs. The fabrication process includes electrospinning of a biodegradable polymer, either poly(L ‐lactide) or poly(lactide‐co‐glycolide), into which the required drug is incorporated, followed by electrochemical deposition of the conducting polymer around the drug‐loaded electrospun nanofibers. Drug release from the nanotubes is achieved by external electrical stimulation of the nanotubes.     

Stabilität antielektrostatischer Beschichtungen auf der Basis von Polyethylendioxithiophenen

Stability of antielectrostatic coatings on basis of polyethylenedioxythiophene Antielectrostatic properties of products manufactured from polymer materials are of great relevance for applications. It has been demonstrated for the engineering polymer polyamide 6 and the high temperature resistant polymer polyethersulphone that by coating them with polyethylenedioxythiophene an electrical conductivity can be achieved which is sufficient for antielectrostatic applications. Due to chemical ageing of the electrical conducting polymer the surface resistance of the coated specimen increases. The change of the electrical resistance with time was measured for various temperatures, layer thicknesses, and resin formulations. The ageing can be described by an Arrhenius behaviour. By this relationship an estimation of the change in resistance under different conditions of application is feasible.     

A Template‐Free Method Towards Conducting Polymer Nanostructures

Conducting polymer nanostructures have recently received special attention in nanoscience and nanotechnology because of their highly π‐conjugated polymeric chains and metal‐like conductivity, such that they can be regarded not only as excellent molecular wires, but also as basic units for the formation of nanodevices. Although various approaches, such as hard‐template methods, soft‐template methods, electrospinning technology, and so on are widely employed to synthesize or fabricate conducting polymer nanostructures and their composite nanostructures, each of the currently used methods possess disadvantages. Therefore, finding a facile, efficient, and controlled method of forming conducting polymer nanostructures is desirable. Similar to other nanomaterials, the effect of size (in these cases 1–100 nm) on the properties of the conducting polymer nanostructures must be considered. Electrical measurements of single nanotubes or nanowires are desirable in order to be able to understand the pure electrical properties of conducting polymer nanostructures. Compared with bulk conducting polymers, conducting polymer nanostructures are expected to display improved performance in technological applications because of the unique properties arising from their nanometer‐scaled size: high conductivity, large surface area, and light weight. Thus, it is also desirable to develop promising applications for conducting polymer nanostructures. In accordance with the issues described above, our research focuses on a new synthesis method to form conducting polymer nanostructures and on the related formation mechanism of the resultant nanostructures. The electrical and transport properties of single nanotubes of conducting polymer, measured by a four‐probe method, and promising applications of such template‐free‐synthesized conducting polymer nanostructures as new microwave absorbing materials and sensors guided by a reversible wettability are also of interest. This article reports some of our main results and reviews some important contributions of others.

     

Local metallic conductivity of thin polyimide films as a result of “soft” electrical breakdown

The electrical breakdown of a thin polyimide film between metal electrodes has been investigated under conditions of strong confinement of the breakdown current. The result of this “soft” electrical breakdown is a local, highly conducting channel in the insulating film implanted in the polymer and consisting of a compound of carbon and metal from the electrodes. It is shown that the polymer channel is converted to the superconducting state by the superconducting properties of the metal from the electrodes. Pis’ma Zh. Tekh. Fiz. 23, 8–12 (July 26, 1997)     

Preparation and characterization of novel polypyrrole-nanotube/polyaniline free-standing composite films via facile solvent-evaporation method

Polyaniline (PANI) is an important conducting polymer and has drawn much attention for its inexpensiveness and chemical stability in the conducting state but its conductivity is rather low. Another well-known conducting polymer is polypyrrole (PPy) with a much higher electrical conductivity but it is hard to prepare films using PPy alone due to its poor film-forming ability. In this work, novel polypyrrole-nanotube (PPy-NT)/polyaniline (PANI) composite films are prepared via a facile solvent-evaporation method. The influence of the PPy-NT content is examined on the film structure, morphology, electrical and mechanical properties. It is shown that PPy nanotubes (PPy-NTs) are uniformly distributed in the PANI matrix. The electrical conductivity is greatly enhanced by 10.2 times by the addition of 10 wt.% PPy nanotubes. Moreover, the mechanical ductility is significantly increased by the addition of PPy nanotubes.     

On the optical and electrical properties of rf and a.c. plasma polymerized aniline thin films

Polyaniline is a widely studied conducting polymer and is a useful material in its bulk and thin film form for many applications, because of its excellent optical and electrical properties. Pristine and iodine doped polyaniline thin films were prepared by a.c. and rf plasma polymerization techniques separately for the comparison of their optical and electrical properties. Doping of iodine was effectedin situ. The structural properties of these films were evaluated by FTIR spectroscopy and the optical band gap was estimated from UV-vis-NIR measurements. Comparative studies on the structural, optical and electrical properties of a.c. and rf polymerization are presented here. It has been found that the optical band gap of the polyaniline thin films prepared by rf and a.c. plasma polymerization techniques differ considerably and the band gap is further reduced byin situ doping of iodine. The electrical conductivity measurements on these films show a higher value of electrical conductivity in the case of rf plasma polymerized thin films when compared to the a.c. plasma polymerized films. Also, it is found that the iodine doping enhanced conductivity of the polymer thin films considerably. The results are compared and correlated and have been explained with respect to the different structures adopted under these two preparation techniques.     

Mechanical and electrical behaviors of polymer particles. Experimental study of the contact area between two particles. Experimental validation of a numerical model

The present paper is devoted to the analysis of mechanical and electrical behaviors observed on particulate polymer granular materials. The constituting particles obtained these physical properties by coating the polymer spherical substrate with a conducting polymer: polypyrrole (PPy) which confers electrical conducting properties to the particle, while preserving its mechanical properties. Particle contacts dominate the behavior of the granular media and, consequently, size, morphology, roughness and plasticity of the particles play a crucial role in this behavior. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used to study the surface state and the contact area between neighbors. An experimental set up, based on the measurement of the displacement of contacting particles subjected to a normal force and of the variation of the electrical resistance of the packing, allowed the study of both the mechanical and electrical behaviors of the particle system. The experimental results took into account the plastic deformation under varying loading and unloading conditions; they were consistent with theories of contact mechanics, thus validating the existing models.     

Optimisation of hybridisation effect in graphene reinforced polymer nanocomposites

This article focuses on the optimisation of electrical and mechanical properties of hybrid blends of polyoxymethylene (POM) as primary thermoplastic matrix, polypyrrole (PPY) as secondary conducting polymer and graphene (G) as reinforcement. An initial Taguchi analysis was performed with a focus on improving electrical conductivity (σ) and tensile strength. A mixture analysis using ‘simplex’ statistical design was applied to develop an experimental subset that identified an optimal combination in weight-percentage. Both electrical and mechanical properties were improved by the addition of PPY and graphene particles due to hybridisation mechanism as well as double percolation threshold. The maximum electrical conductivity of 0.95 S cm^?1 was achieved with POM reinforced with 3 wt.% of G and 2.5 wt.% of PPY loading. The mechanical properties were found to be increased with increase in addition of both G and PPY.     

On polyethylene–polyaniline composites

Mechanical tests (elongation at break and tensile strength), DC electrical conductivity, and electron spin resonance (ESR) investigations on polyethylene–polyaniline blends are reported. While the concentration of the conducting polymer in the blend is raised, the DC electrical conductivity is increased, and the mechanical properties (tensile strength and elongation at break) are depressed. An universal expression for the dependence of mechanical and electrical properties on the concentration of conducting particles is empirically suggested and supported by experimental data. The ESR spectra are single lines, located close to the g=2.0 value and assigned to the conduction electrons (with uncoupled electronic spins). The reduced asymmetry of the resonance supports the presence of mesoscopic conducting domains. The features of ESR spectra and the connection between ESR parameters and DC conductivity reflects the major role of polarons hopping in the electron transport and rules out the presence of both low and high spin bipolarons.     

Highly conductive graphene-based segregated composites prepared by particle templating

We use capillary-driven particle level templating and hot melt pressing to disperse few-layer graphene flakes within a polystyrene matrix to enhance the electrical conductivity of the polymer. The conducting pathways provided by the graphene located at the particle surfaces through contact of the bounding surfaces allow percolation at a loading of less than 0.01 % by volume. This method of distributing graphene within a matrix overcomes the need to disperse the sheet-like conducting fillers isotropically within the polymer, and can be scaled up easily.     

Anisotropic electrical conduction in gum arabica—a biopolymer

Gum arabica, a natural biopolymer, exhibits electrical properties like conducting polymers. Earlier investigations show its ion-conducting superionic nature rather than its proton conducting nature with room temperature d.c. conductivity 10e−07 S/cm. The present study shows more interesting electrical characters gum arabica, XRD study of its powdered sample shows an amorphous nature and that of caste and textured specimen show an increased RDF. The same indicates a possibility of crystallization, which is a difficult task for this solid gel-like substance. Specimen with preferred molecular orientation is prepared by casting thin layer of gum arabica on scratched (10 μm) metal electrode and glass substrate. The desired anisotropy thus produced is confirmed by XRD study. The morphology of ordinarily caste specimen and textured specimen were studied and compared by SEM study. The impedance spectroscopy carried over this specimen shows an electrical conductivity like that of crystalline conducting polymer. Transverse and longitudinal electrical conductivity with their frequency dispersion show marked difference. Its further investigation and applications are under progress.     

Metal oxide/polyaniline nanocomposites: Cluster size and composition dependent structural and magnetic properties

Nanocomposites of iron oxide with conducting polymer in the form of powders of varying compositions have been studied to understand the effects of particle size, cluster size and magnetic inter-particle interactions. The sizes of the nanoparticles were estimated to be ∼ 10–20 nm from the X-ray diffraction (XRD) and the transmission electron micrographs (TEM). XRD shows a single crystalline phase for the γ-Fe₂O₃. The presence of conducting polymer was confirmed through Fourier transform infrared (FTIR) spectroscopy. The amount of polymer present in the composite, the transition temperature of iron oxide and the thermal stability of polymer was determined through thermogravimetric and differential thermal analysis (TGA-DTA). The room temperature magnetic hysteresis measurements show reduction in saturation magnetization with increasing polymer concentrations. A low value of coercivity was observed for low polymer composites. On increasing the polymer concentration, the coercivity and remanence become negligible indicating a superparamagnetic phase at room temperature. Beyond a certain composition, the system shows paramagnetic behaviour which is also confirmed through zero field cooled-field cooled (ZFC-FC) measurements. We also report preliminary results on the magnetic properties of self standing sheets prepared using γ-Fe₂O₃ and NiFe₂O₄ nanoparticles and conducting polymers.     

离子注入技术改性聚合物薄膜的研究进展

离子注入技术改性聚合物薄膜在电子及电器工程中有着巨大的潜在应用价值。综述了近年来聚合物薄膜经离子注入后在导电性能、光学性能、导磁性能及表面力学机械性能等方面的最新进展。分析了注入离子与聚合物相互作用的物理过程,并指出了该领域存在的问题及发展方向。     

Enhancing the thermoelectric performance by defect structures induced in p-type polypyrrole-polyaniline nanocomposite for room-temperature thermoelectric applications

Organic thermoelectric materials mainly conducting polymers are green materials that can convert heat energy into electrical energy and vice versa at room temperature. In the present work, we investigated the thermoelectric properties of polymer nanocomposite of polypyrrole (PPy) and polyaniline (PANI) (PPy/PANI) by varying the pyrrole: aniline monomer ratios (60:40, 50:50, and 40:60). The PPy/PANI composite is prepared by in-situ chemical polymerization of PPy on PANI dispersion. It has been observed that the combination of two conducting polymers has enhanced the electrical and thermal properties in the PPy/PANI composite due to the strong π–π stacking and H-bonding interaction between the conjugated structure of PPy and conjugated structure of PANI. The maximum electrical conductivity of 14.7 S m^?1 was obtained for composite with high pyrrole content, whereas the maximum Seebeck coefficient of 29.5 μV K^?1 was obtained for composite with high aniline content at 366 K. Consequently, the PPy/PANI composite with pyrrole to aniline monomer ratio of 60:40 exhibits the optimal electrical conductivity, Seebeck coefficient, and high power factor. As a result, the maximum power factor of 2.24 nWm^?1 K^?2 was obtained for the PPy/PANI composite at 60:40 pyrrole to aniline monomer ratio, which is 29 times and 65.8 times higher than PPy (0.077 nWm^?1 K^?2) and PANI (0.034 nWm^?1 K^?2), respectively.

     

Rheological and mechanical properties of carbon nanotube/Graphite/SS316L/polypropylene nanocomposite for a conductive polymer composite

Highly filled conductive fillers (>60 vol%) for conductive polymer composites (CPCs) cause the degradation of rheological and mechanical properties. This study investigated the rheological properties of highly filled metal powder (SS316L) in a polymer matrix composite combined with carbon nanotubes (CNTs) and Graphite (G). The effects of filler concentrations and chemical functionalization on the mechanical and electrical properties of the resulting CPC were determined. Feedstocks with different concentrations were injection molded, and the molded specimens were subjected to tests of tensile strength, three-point bending, hardness, and three-point probe electrical conductivity. The feedstock of CNTs/G/SS316L can be injection molded from 28 vol% polypropylene (PP). The functionalized CPC shows higher strength and elongation than as-produced CPC based on the tensile and flexural tests. The highest flexural and tensile strengths are 80 and 35 MPa, respectively. The functionalized CPC also exhibits higher hardness and better electrical properties than as-produced CPC. Thus, functionalization with CNTs and Graphite enable the reinforcement and formation electrical conducting networks between metal- and carbon-based fillers within a polymer matrix.     

Electrical conductivity of carbon-polymer composites as a function of carbon content

The electrical conductivity of carbon particle-filled polymers was measured as a function of carbon content to find a break point of the relationships between the carbon content and the conductivity. The conductivity jumps by as much as ten orders of magnitude at the break point. The critical carbon content corresponding to the break point varies depending on the polymer species and tends to increase with the increase in the surface tension of polymer. In order to explain the dependency of the critical carbon content on the polymer species, a simple equation was derived under some assumptions, the most important of which was that when the interfacial excess energy introduced by carbon particles into the polymer matrix reaches a universal value, g ^*, the carbon particles begin to coagulate so as to avoid any further increase of the energy and to form networks which facilitate electrical conduction. The equation well explains the dependency through surface tension, as long as the difference of the surface tensions between the carbon particles and the polymer is not very small.     

Fast electrical response to volatile organic compounds of 2D Au nanoparticle layers embedded into polymers

The conductivity of polymer–metal nanocomposites close to the percolation threshold is very sensitive to changes in the metal nanoparticle distances. Here the technical feasibility of a novel type of easy to prepare polymer–metal nanocomposite sensor is explored, which shall be able to detect a unique signal for various volatile organic compounds (VOCs) exhibiting a fast and reversible response. The composite consists of a nearly 2-dimensional Au nanoparticle layer near the percolation threshold thermally embedded into a thermoplastic polymer film. The sensoric response is based on the swelling behavior of the polymeric matrix upon exposure to the organic vapor molecules. Different from conventional nanocomposite sensors that require long-range diffusion of the volatile compound into the bulk of the matrix, the electrical response here only requires the penetration of the VOC a few nanometer below the surface thus causing a rapid detection. The degree of swelling depends on the type of polymer and VOC used as well as on the vapor pressure of the VOC leading to a characteristic response of each polymer to a specific VOC. This enables a “fingerprint” detection of different VOCs by an array of different polymer nanocomposite combined into one sensoric device.     

Formation of conducting polymer nanostructures with the help of surfactant crystallite templates

An extremely simple approach is described here to synthesize bulk quantities of conducting polymer microspirals assembled from nanofibers by in situ chemical oxidative polymerization in the presence of a conventional surfactant. It is worth noting that the surfactant used in our approach is in crystalline state, which is quite different from micellar state in emulsional polymerization reported previously. The growth mechanism of the conducting polymer is proposed.     

First evidence of crystalline structure in conducting polythiophene

In order to optimize the properties of organic conducting polymers we analysed the effect of structure and dopant. The substitution of the carbon atoms in thiophene leads to a higher regularity in the corresponding polymer, obtained by electrochemical oxidation. The trifluoromethylsulphonate anion appears to be the best fitting dopant, allowing a 12 doping level of the polymer. Transmission electron microscopy reveals crystal patterns for this highly doped polymer. The obtained electron diffraction and X-ray data are consistent with a hexagonal lattice. The discussion of these results lead us to propose a coil structure for this organic conducting polymer.     

Humidity-sensing properties of conducting polypyrrole-silver nanocomposites

We report here the humidity-sensing characteristics of conducting polypyrrole (PPY)-silver nanocomposites prepared by wet-chemical technique. Addition of silver into the conducting polymer network shows remarkable change in resistance with relative humidity (RH). The resistance of PPY-silver nanocomposites is found to increase with RH till a threshold value, above which the resistance tends to decrease. The threshold RH value is significantly reduced with the increase in silver concentration into the conducting polymer network. The modified metal–polymer interface and the associated interfacial water molecules play the critical role in determining the electrical transport and hence the humidity-response characteristics of the nanocomposites.