Papers by Author: Petr Slobodian

Abstract: Carbon nanotubes in the form of entangled network can be used as a multifunctional composite material for a wide range of using. A new and perspective usage is a passive antenna and gas sensing element. The antenna works well at 1.284 GHz. The local reflection minimum is 11.48 dB. The reflection coefficient r=0.2667. The transmission power in this frequency is 93%. Multiwall carbon nanotubes (MWCNT) network Buckypaper was made by the vacuum filtration method of MWCNT aqueous suspension. The sensitivity of multi-wall carbon nanotube (MWCNT) networks of randomly entangled pure and HNO₃ oxidized nanotubes to polar and nonpolar organic vapors (ethanol, heptane), has been investigated by resistance measurements. The results demonstrate that the network electrical resistance increases when exposed to organic solvent vapors, and a reversible reaction is observed when the sample is removed from the vapors. The investigated MWCNT networks could be potentially used as sensing elements for sensitive and selective organic vapor detection.

Abstract: The sensing properties of pristine and hexamethylene diamine (HDA)-treated multiwall carbon nanotube networks (MWCNT-Ns) to selected primary, secondary (sec-) and tertiary (ter-) alcohols were examined by resistance measurements. It was seen that sensor responses, S (%), of MWCNT (HDA)-N to these alcohols were much higher than those of the pristine network. An increase in the S (%) values per mm Hg of both networks was observed from propanol to butanol, when their values from primary alcohols to sec-/tert-ones decreased due to the change in the interaction area of these alcohols with the MWCNT-Ns.

Abstract: The effect of oxidation of multi-walled carbon nanotubes by KMnO₄ on the electrical resistance of a nanotube network/polyurethane composite subjected to bending has been studied. In this respect, the main achievement is a multiple increase of gauge factor for the evaluating electromechanical properties of the composite after nanotube oxidation with KMnO₄. It indicates favorable properties of the composite for its use as a high-deformation strain-sensing element.

Abstract: A highly deformable composite composed of a network of electrically-conductive entangled carbon nanotubes embedded in elastic polyurethane for sensing tensile deformation by changes in strain has been prepared. The testing has shown that the composite can be extended as by much as 400 % during which the electrical resistance increases more than 270 times. The high strain sensing can be attributed to the network cracking upon extension. To understand the cracking mechanism and explain the resistance change, the structural changes of networks made of pristine carbon nanotubes (as well as functionalized multi-walled) were examined. The microscopic observation of crack formation and resistance change of the networks correlates well with the amount of cracking.

Abstract: Polyaniline thin films are chemically functionalized by nucleophilic addition of thiols beareing different functional groups: carboxylic, amine, -dodecyl and sulfonic. The modification is tested using FTIR and XPS spectroscopy. Then, the films are used as resistive sensors for different volatile organic compounds in a static measuring system. The sensitivity of conducting polymers to alcohols and heptane is strongly affected by the chemical functionalization of the materials. Polyaniline show an increasing signal when the chain length of different alcohols is increased. The incorporation of hydrophilic groups on the PANI chains seems to maintain the trend. On the other hand, the polymer modified with a long alkyl chain (PANI-DOT) show negative response for methanol and the signal increases up to propanol to decrease for longer chains. PANI-DOT show the largest signal for heptane of all polymers tested. Therefore, the functional group attached to the conductive polymer chain can be used to tune the molecular sensitivity of the resistive sensor

Abstract: Multi-walled carbon nanotubes networks (MWCNTs) were used as a layer for organic vapor detection. The sensor detects volatile organic compounds (VOC). The gas sensing by MWCNTs is measured by means of macroscopic electrical resistance. The selected solvents had different polarities and volume fractions of saturated vapors. The electrical resistance of MWCNTs increases when exposed to organic solvent vapors, and a reversible reaction is observed when the MWCNT is removed from the vapors. The MWCNTs were modified by means of plasma treatment. For modifications RF plasma in O₂ at 50 Pa and an afterglow configuration were used. The modified MWCNTs show an increase in sensitivity caused by creating carboxylic groups on the surface of the carbon nanotubes. It leads, for example, to enhancement of the sensitivity from usual 30 % for heptane at RT to more than 200% after plasma treatment in O₂ for 10s.

Abstract: The conductance properties of multi-walled carbon nanotube mats and their polystyrene composite were examined to investigate the mechanism of conduction and the specific role of the supporting polymer. By measuring the temperature dependence of the conductance, it was found that the conduction mechanism in carbon nanotube mat follows the series heterogeneous model when the conductance is described as the sum of metallic and barrier portions of the conduction path. This mechanism is affected by the polymeric portion of the composite, since the temperature dependence of the composite conductance is decreased.

Abstract: Gas sensing properties of networks made of carbon black, carbon nanofibers and carbon multi-walled carbon nanotubes are tested. The networks reaction to vapors of volatile organic compounds is measured through their change of electrical resistance. The measured resistance increase is up to 27.7 % for carbon black, 40% for carbon nanofibers and 47.7% for multi-walled carbon nanotubes.

Abstract: Electrical properties and morphology of carbon black (CB) filled ethylene-butyl-acrylate copolymer (EBA) composites were studied in compact and chemically foamed versions. Conductivity percolation threshold for foamed composites was lowered by five weight percent of carbon black concentration. It means that the same conductivity values were achieved at reduced concentration of filler than for non-foamed version of composite. As a result semiconducting material with reduced density (weight) and content of carbon black is obtained. The sensitivity of foamed composite conductivity to mechanical stimulus induced by uniaxial compression was observed.

Abstract: A sensing element made of conductive composite created by an entangled network of electrically conductive carbon nanotubes embedded in polyurethane was used for simultaneous measurements of the pressure between the shoe and floor as well as the extension of the leg at the knee joint during marching. The results recorded as sensor resistance change show reasonable reversibility of the basic sensor characteristics, which gives potential for practical applications.