Petr Slobodian

Poly(methyl methacrylate)/multi-wall carbon nanotubes composites prepared by solvent cast technique : Composites electrical percolation threshold

Polymer composites based on poly(methyl metacrylate)/multi-wall carbon nanotubes, (PMMA/MWNT), were prepared by the solvent cast technique from dispersions of MWNT in PMMA solutions. Three different solvents like toluene, chloroform and acetone were selected to solve PMMA, covering a broad range of Hansen solubility parameters. Composite mixing was done by sonication of solutions with MWNT in a broad concentration range up to 20 wt.% of MWNT. Electrical conductivity of composites as a function of MWNT concentration was measured. The different percolation thresholds were found for used systems like PMMA/solvent/MWNT which were found to be related to values of Hansen solubility parameters. Increasing the dispersion component, together with lower values of polar and hydrogen bonding components, leads to a lower value of percolation threshold.

A Flexible Multifunctional Sensor Based on Carbon Nanotube/Polyurethane Composite

A sensor was made of a polymer composite composed of electrically-conductive carbon nanotubes embedded in elastic polyurethane. The composite was prepared using a polyurethane filter membrane, enmeshing it, and melding together with carbon nanotubes. Testing has shown that the composite can be elongated as much as 400% during which the electrical resistance is increased 270 times. The composite is also sensitive to compression and to organic solvent vapors. These properties indicate the composite could have applications as a highly-deformable strain and chemical vapors sensing element and also as flexible electromagnetic shielding or protection against lightning. As an example of the use of the composite as a strain sensor, the pressure variation between a shoe and floor during walking and knee flexion during cycling has been monitored.

Highly enhanced vapor sensing of multiwalled carbon nanotube network sensors by n -butylamine functionalization

The sensing of volatile organic compounds by multiwall carbon nanotube networks of randomly entangled pristine nanotubes or the nanotubes functionalized by n-butylamine, which were deposited on polyurethane supporting electrospinned nonwoven membrane, has been investigated. The results show that the sensing of volatile organic compounds by functionalized nanotubes considerably increases with respect to pristine nanotubes. The increase is highly dependent on used vapor polarity. For the case of highly polar methanol, the functionalized MWCNT network exhibits even more than eightfold higher sensitivity in comparison to the network prepared from pristine nanotubes.

Thermoelectric properties of carbon nanotube and nanofiber based ethylene-octene copolymer composites for thermoelectric devices

Polymer composites have been created from multiwalled carbon nanotubes or carbon nanofibers and ethylene-octene copolymer. The composites have thermoelectric properties and exhibit thermoelectric effect, that is, the conversion of temperature differences into electricity. The thermoelectric efficiency of created composites with nanotube or nanofiber concentration of 30wt% evaluated by a thermoelectric power at room temperature is 13.3 µV/K and 14.2 µV/K, respectively. The flexible thermoelectric device (thermopile) was constructed with three different composite legs to produce electric current and the output voltage was measured in the range of temperature difference from -15 to 25°C.

Carbon nanotube- and carbon fiber-reinforcement of ethylene-octene copolymer membranes for gas and vapor separation.

Gas and vapor transport properties were studied in mixed matrix membranes containing elastomeric ethylene-octene copolymer (EOC or poly(ethylene-co-octene)) with three types of carbon fillers: virgin or oxidized multi-walled carbon nanotubes (CNTs) and carbon fibers (CFs). Helium, hydrogen, nitrogen, oxygen, methane, and carbon dioxide were used for gas permeation rate measurements. Vapor transport properties were studied for the aliphatic hydrocarbon (hexane), aromatic compound (toluene), alcohol (ethanol), as well as water for the representative samples. The mechanical properties and homogeneity of samples was checked by stress-strain tests. The addition of virgin CNTs and CFs improve mechanical properties. Gas permeability of EOC lies between that of the more permeable PDMS and the less permeable semi-crystalline polyethylene and polypropylene. Organic vapors are more permeable than permanent gases in the composite membranes, with toluene and hexane permeabilities being about two orders of magnitude higher than permanent gas permeability. The results of the carbon-filled membranes offer perspectives for application in gas/vapor separation with improved mechanical resistance.

Effect of compressive strain on electric resistance of multi-wall carbon nanotube networks

The network of entangled multi-wall carbon nanotubes is shown as a conductor whose resistance is sensitive to compressive strain, both in the course of strain growth and when loading/unloading cycles are imposed. If the compression is applied, the resistance decrease is up to 25% at the maximum applied deformation. The experimental data are analysed using the Weibull distribution model and a contact network model to get an estimate of the contact resistance between carbon nanotubes and the formation of contacts in the course of compression.

Volume and enthalpy relaxation in a-PMMA after temperature up-jumps

Abstractthe volume and enthalpy relaxation in a-PMMA subjected to temperature jumps in tg region has been analysed. The measured H and V data were compared with respect to aging time and proportionality between them as a slope of (∂H/∂V)T dependencies has been found. According to previous works the slope was identified as an apparent bulk modulus, Ka. This method is applied to aging following temperature up-jumps after consolidation periods of varying lengths. the main finding is a marked increase of Ka with consolidation time, approaching a limiting value in an asymptotic fashion.

Plasma-enabled sensing of urea and related amides on polyaniline

The atmospheric pressure plasma jet (APPJ) was used to enhance the sensitivity of industrially important polyaniline (PANI) for detection of organic vapors from amides. The gas sensing mechanism of PANI is operating on the basis of reversible protonation or deprotonation, whereas the driving force to improve the sensitivity after plasma modifications is unknown. Herein we manage to solve this problem and investigate the sensing mechanism of atmospheric plasma treated PANI for vapor detection of amides using urea as a model. The results from various analytical techniques indicate that the plausible mechanism responsible for the improved sensitivity after plasma treatment is operating through a cyclic transition state formed between the functional groups introduced by plasma treatment and urea. This transition state improved the sensitivity of PANI towards 15 ppm of urea by a factor of 2.4 times compared to the non-treated PANI. This plasma treated PANI is promising for the improvement of the sensitivity and selectivity towards other toxic and carcinogenic amide analytes for gas sensing applications such as improving material processing and controlling food quality.

Enhanced strain-dependent electrical resistance of polyurethane composites with embedded oxidized multiwalled carbon nanotube networks

The effect of different chemical oxidation of multiwalled carbon nanotubes with H2O2, HNO3, and KMnO4 on the change of electrical resistance of polyurethane composites with embedded oxidized nanotube networks subjected to elongation and bending has been studied. The testing has shown about twenty-fold increase in the electrical resistance for the composite prepared from KMnO4 oxidized nanotubes in comparison to the composites prepared from the pristine and other oxidized nanotubes. The evaluated sensitivity of KMnO4 treated composite in terms of the gauge factor increases with strain to nearly 175 at the strain 11%. This is a substantial increase, which ranks the composite prepared from KMnO4 oxidized nanotubes among materials as strain gauges with the highest electromechanical sensitivity. The observed differences in electromechanical properties of the composites are discussed on basis of their structure which is examined by the measurements of Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscope. The possible practical use of the composites is demonstrated by monitoring of elbow joint flexion during two different physical exercises.

An electrically conductive and organic solvent vapors detecting composite composed of an entangled network of carbon nanotubes embedded in polystyrene

A composite composed of electrically conductive entangled carbon nanotubes embedded in a polystyrene base has been prepared by the innovative procedure, when the nonwoven polystyrene filter membrane is enmeshed with carbon nanotubes. Both constituents are then interlocked by compression molding. The mechanical and electrical resistance testing show that the polymer increases nanotube network mechanical integrity, tensile strength, and the reversibility of electrical resistance in deformation cycles. Another obvious effect of the supporting polymer is the reduction of resistance temperature dependence of composite and the reproducibility of methanol vapor sensing.