Vanadium dioxide (VO2) is a phase transition material that undergoes semiconductor-to-metal transition at the temperature of about 68 °C. This extraordinary feature triggered intensive research focused on the controlled synthesis of VO2. In this study, we introduce and investigate an original linker- and solvent-free strategy enabling the production of highly porous VO2 nanoparticle-based films. This technique combines a gas-phase synthesis of vanadium nanoparticles and their subsequent atmospheric pressure thermal oxidation. It is shown that the thermochromic behaviour of such produced nanomaterial is at the fixed oxidation temperature strongly dependent on the oxidation time. Concerning this, it was found that there exists an optimal oxidation time (60 s in our study) that assures the production of crystalline VO2 nanoparticles with the highest, reproducible and temporally stable semiconductor-to-metal transition with the resistive switching ratio close to 2 orders of magnitude and dramatic switching of optical properties in the near infra-red spectral region.

• Keywords
• Gas aggregation source, Nanoparticles, Resistive switching, Thermochromic materials, Vanadium dioxide,
• Publication type
• Journal Article MeSH

Iron microparticles were coated with polypyrrole in situ during the chemical oxidation of pyrrole with ammonium peroxydisulfate in aqueous medium. A series of hybrid organic/inorganic core-shell materials were prepared with 30-76 wt% iron content. Polypyrrole coating was revealed by scanning electron microscopy, and its molecular structure and completeness were proved by FTIR and Raman spectroscopies. The composites of polypyrrole/carbonyl iron were obtained as powders and characterized with respect to their electrical properties. Their resistivity was monitored by the four-point van der Pauw method under 0.01-10 MPa pressure. In an apparent paradox, the resistivity of composites increased from the units Ω cm for neat polypyrrole to thousands Ω cm for the highest iron content despite the high conductivity of iron. This means that composite conductivity is controlled by the electrical properties of the polypyrrole matrix. The change of sample size during the compression was also recorded and provides a parameter reflecting the mechanical properties of composites. In addition to conductivity, the composites displayed magnetic properties afforded by the presence of iron. The study also illustrates the feasibility of the polypyrrole coating on macroscopic objects, demonstrated by an iron nail, and offers potential application in the corrosion protection of iron. The differences in the morphology of micro- and macroscopic polypyrrole objects are described.

• Keywords
• carbonyl iron microparticles, conducting polymer, conductivity, corrosion protection, hybrid core–shell composites, iron, magnetic properties, polypyrrole, resistivity,
• Publication type
• Journal Article MeSH

Hybrid organic/inorganic conducting and magnetic composites of core-shell type have been prepared by in-situ coating of nickel microparticles with polypyrrole. Three series of syntheses have been made. In the first, pyrrole was oxidised with ammonium peroxydisulfate in water in the presence of various amounts of nickel and the composites contained up to 83 wt% of this metal. The second series used 0.1 M sulfuric acid as a reaction medium. Finally, the composites with polypyrrole nanotubes were prepared in water in the presence of structure-guiding methyl orange dye. The nanotubes have always been accompanied by the globular morphology. FTIR and Raman spectroscopies confirmed the formation of polypyrrole. The resistivity of composite powders of the order of tens to hundreds Ω cm was monitored as a function of pressure up to 10 MPa. The resistivity of composites slightly increased with increasing content of nickel. This apparent paradox is explained by the coating of nickel particles with polypyrrole, which prevents their contact and subsequent generation of metallic conducting pathways. Electrical properties were practically independent of the way of composite preparation or nickel content and were controlled by the polypyrrole phase. On the contrary, magnetic properties were determined exclusively by nickel content. The composites were used as a solid phase to prepare a magnetorheological fluid. The test showed better performance when compared with a different nickel system reported earlier.

• Keywords
• conductivity, hybrid composites, magnetization, magnetorheology, nickel microparticles, polypyrrole, resistivity,
• Publication type
• Journal Article MeSH

This paper reports the conversion of a waste to a conducting material, exploiting the ability to adsorb pollutant organic dyes. Leather waste was carbonized at 800 °C in an inert nitrogen atmosphere. The resulting biochar was used for in-situ deposition of polypyrrole nanotubes produced by the oxidative polymerization of pyrrole in the presence of methyl orange. The composites of carbonized leather with deposited polypyrrole nanotubes of various composition were compared with similar composites based on globular polypyrrole. Their molecular structure was characterized by infrared and Raman spectra. Both conducting components formed a bicontinuous structure. The resistivity was newly determined by a four-point van der Pauw method and monitored as a function of pressure applied up to 10 MPa. The typical conductivity of composites was of the order of 0.1 to 1 S cm-1 and it was always higher for polypyrrole nanotubes than for globular polypyrrole. The method also allows for the assessment of mechanical features, such as powder fluffiness. The conductivity decreased by 1-2 orders of magnitude after treatment with ammonia but still maintained a level acceptable for applications operating under non-acidic conditions. The composites were tested for dye adsorption, specifically cationic methylene blue and anionic methyl orange, using UV-vis spectroscopy. The composites were designed for future use as functional adsorbents controlled by the electrical potential or organic electrode materials.

• Keywords
• Raman spectra, bicontinuous structure, carbonized leather, conducting polymer, conductivity, dye adsorption, globular polypyrrole, polypyrrole nanotubes, resistivity,
• Publication type
• Journal Article MeSH

Combining highly conducting one-dimensional nanostructures of polypyrrole with cellulose nanofibers (CNF) into flexible films with tailored electrical conductivity and mechanical properties presents a promising route towards the development of eco-friendly electromagnetic interference shielding devices. Herein, conducting films with a thickness of 140 μm were synthesized from polypyrrole nanotubes (PPy-NT) and CNF using two approaches, i.e., a new one-pot synthesis consisting of in situ polymerization of pyrrole in the presence of structure guiding agent and CNF, and a two-step synthesis, in which CNF and PPy-NT were physically blended. Films based on one-pot synthesis (PPy-NT/CNFin) exhibited higher conductivity than those processed by physical blending, which was further enhanced up to 14.51 S cm-1 after redoping using HCl post-treatment. PPy-NT/CNFin containing the lowest PPy-NT loading (40 wt%), thus the lowest conductivity (5.1 S cm-1), displayed the highest shielding effectiveness of -23.6 dB (>90 % attenuation), thanks to the good balance between its mechanical properties and electrical conductivity.

• Keywords
• Cellulose nanofibers, Composite films, Electrical conductivity, Electromagnetic interference shielding, Polypyrrole nanotubes,
• Publication type
• Journal Article MeSH

The carbonization of collagen-based leather waste to nitrogen-containing carbon is reviewed with respect to the preparation, characterization of carbonized products, and applications proposed in the literature. The resulting nitrogen-containing carbons with fibrous morphology have been used as adsorbents in water pollution treatment, in electrocatalysis, and especially in electrodes of energy-storage devices, such as supercapacitors and batteries. Although electrical conductivity has been implicitly exploited in many cases, the quantitative determination of this parameter has been addressed in the literature only marginally. In this report, attention has been newly paid to the determination of conductivity and its dependence on carbonization temperature. The resulting powders cannot be compressed into pellets for routine conductivity determination. A new method has been used to follow the resistivity of powders as a function of pressure up to 10 MPa. The conductivity at this pressure increased from 9.4 × 10-8 S cm-1 for carbonization at 500 °C to 5.3 S cm-1 at 1000 °C. The conductivity of the last sample was comparable with conducting polymers such as polypyrrole. The carbonized leather thus has the potential to be used in applications requiring electrical conduction.

• Keywords
• activation, carbonization, char, conductivity, leather waste, nitrogen-containing carbon, pyrolysis,
• Publication type
• Journal Article MeSH
• Review MeSH

The growing demand for polymer composites and their widespread use is inevitably accompanied by the need to know their degradation behavior over a sufficiently long period of time. This study focuses on commercial glass fiber rovings, which were stored in the indoor environment for up to 11 years. Fibers with different storage times, from fresh up to the oldest, were used to produce unidirectional fiber-reinforced polyester composites that were characterized to determine their shear and flexural properties dependent on fiber storage time. A significant decrease in shear strength was observed throughout the aging of the fibers, down to a decrease of 33% for the oldest fibers. An important finding, however, was that the significant decrease in shear strength was only partially reflected in the flexural strength, which corresponded to a decrease of 18% for the oldest fibers at consistent flexural modulus.

• Keywords
• environmental degradation, glass fibers, mechanical properties, polymer-matrix composites (PMCs),
• Publication type
• Journal Article MeSH

Melamine sponges were coated with polypyrrole during the in situ polymerization of pyrrole. The precipitation polymerization was compared with the dispersion mode, that is, with the preparation in the presence of poly(N-vinylpyrrolidone) and nanosilica as colloidal stabilizers. The coating of sponges during the dispersion polymerization leads to the elimination of the undesired polypyrrole precipitate, improved conductivity, and increased specific surface area. The sponges were tested with respect to their conductivity and as pressure-sensitive conducting materials with antibacterial performance.

• Publication type
• Journal Article MeSH

The analysis presented in this paper is focused on problems of bond strength as an overall bond quality parameter of industrial adhesives for structural anchoring. In the first part, the problem of bond strength as the most important parameter influencing the final anchor resistance to tension load is described. Further in the text, a new methodology of simplified testing of the strength parameters of adhesives is described. Special test specimens made from steel are repeatedly used in this methodology. Additionally, results of these tests on some new recipes for adhesive are presented. Especially, epoxy resins with special fillers, such as carbon fibres, carbon nanotubes or graphene, were tested. The use of these adhesives in temperatures close to zero degrees Celsius was also tested.

• Keywords
• adhesive, bond stress, bonded anchor, experiment, fillers, tension force,
• Publication type
• Journal Article MeSH

Polypyrrole one-dimensional nanostructures (nanotubes, nanobelts and nanofibers) were prepared using three various dyes (Methyl Orange, Methylene Blue and Eriochrome Black T). Their high electrical conductivity (from 17.1 to 60.9 S cm-1), good thermal stability (in the range from 25 to 150 °C) and resistivity against ageing (half-time of electrical conductivity around 80 days and better) were used in preparation of lightweight and flexible composites with silicone for electromagnetic interference shielding in the C-band region (5.85-8.2 GHz). The nanostructures' morphology and chemical structure were characterized by scanning electron microscopy, Brunauer-Emmett-Teller specific surface measurement and attenuated total reflection Fourier-transform infrared spectroscopy. DC electrical conductivity was measured using the Van der Pauw method. Complex permittivity and AC electrical conductivity of respective silicone composites were calculated from the measured scattering parameters. The relationships between structure, electrical properties and shielding efficiency were studied. It was found that 2 mm-thick silicone composites of polypyrrole nanotubes and nanobelts shield almost 80% of incident radiation in the C-band at very low loading of conductive filler in the silicone (5% w/w). Resulting lightweight and flexible polypyrrole composites exhibit promising properties for shielding of electromagnetic interference in sensitive biological and electronic systems.

• Keywords
• 1D nanostructures, conducting polymers, electromagnetic shielding, microwave region, thermal stability,
• MeSH
• Azo Compounds chemistry   MeSH
• Electromagnetic Radiation * MeSH
• Methylene Blue chemistry   MeSH
• Microscopy, Electron, Scanning MeSH
• Nanostructures chemistry   radiation effects   ultrastructure   MeSH
• Nanotubes chemistry   radiation effects   ultrastructure   MeSH
• Nanofibers chemistry   radiation effects   MeSH
• Polymers chemistry   radiation effects   MeSH
• Pyrroles chemistry   radiation effects   MeSH
• Silicones chemistry   radiation effects   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Azo Compounds MeSH
• Eriochrome Black T MeSH Browser
• methyl orange MeSH Browser
• Methylene Blue MeSH
• Polymers MeSH
• polypyrrole MeSH Browser
• Pyrroles MeSH
• Silicones MeSH