Fluctuation in the surface irregularities is found to be the reason for surface charge formation ... more Fluctuation in the surface irregularities is found to be the reason for surface charge formation by contacting two identical polymers. Higher surface charge is shown to correlate with higher disparity in porosity or surface roughness.
Recent achievements of scientific group of Riga Technical University in collaboration with COINAP... more Recent achievements of scientific group of Riga Technical University in collaboration with COINAPO partners in design, processing and investigation of polyisoprene composites with conductive tubular nanostructures (PCCTN) as prospective materials for completely hyper-elastic (non-rigid) mechanical (pressure, strain) indicators, chemical vapour indicators as well as temperature indicators have been presented. Non-rigid multifunctional sensing materials attract attention of scientists and engineers because of potential possibility to incorporate them in different solid and nonsolid systems for specific parameter control. Previous experience with electro-active materials like ferroelectrics suggests that maximum sensitivity of material to any influence is observed in the vicinity of phase transitions. The percolation transition in PCCTN could be imagined as specific phase transition from electrically insulating state to electrically conductive state. Thus, the maximum sensitivity of PCCTN materials to external thermodynamic forces (ETF) should be expected in the vicinity of percolation threshold. The reversibility of material reaction to ETF should be achieved by positioning conductive tubular nanostructures in the spatial grid by curing of hyper-elastic polymer matrix. Our previous research approved that high structure carbon black PRINTEX XE2 filled composites demonstrate finger pressure sensitive piezoresistivity as well as good organic solvent vapour sensing. Conductive tubular nanostructures originate with variable length to width ratio and high electric conductivity in longitudinal direction of the tubes, which theoretically should make it possible to obtain electric percolation in polymercarbon nanotube composites at very low loads of filler. However recent experience with mechanically dispersed carbon nanotubes shows quite high values of percolation threshold and specific sensing properties. In this work we present an attempt to use ultrasound for improved dispersion of the filler in polyisoprene matrix composite. Multi wall carbon nanotubes (MWCNT) “Aldrich 636835” as well as inorganic nanotubules (IN) Mo6S2I8 and MoO3-X are used as filler. As reference filler PRINTEX XE2 was also used. The noticeable shifting of percolation threshold to lower values of concentration has been achieved for all types of nano-composites. The piezoresistive and chemosensitive behaviour of sonicated nano-composites have been determined and compared with mechanically mixed ones. The obtained results are explained using quantum mechanical charge tunnelling and percolation theory
We investigated a promising material for hydrogen storage and sensing. The material was obtained ... more We investigated a promising material for hydrogen storage and sensing. The material was obtained by exfoliating recycled graphite waste and simultaneously modifying the product with metal impurities (Bi, V, Cu). As a result, graphene sheet stack (GSS) powder was obtained. The material was further processed by hydrothermal annealing and reduction. Raman spectra of the GSS materials are provided to show the presence of graphene-like structures and defects in the exfoliated material. The synthesized graphene material has good semiconductor properties with a low electrical resistance for hydrogen sensing applications.
Nowadays scientific progress and improving of chemical industry has made a big step forward. That... more Nowadays scientific progress and improving of chemical industry has made a big step forward. That means, the possibility of various organic solvents to come in tracheas of workers is growing and it can make irreversible damage to workers organism. Therefore there is a need to design, elaborate and investigate polymer-nanostructured carbon composite (P-NCC), which would serve in factories as a sensor material and would warn workers about health risks or it can help manufacturers control production processes. Sensor material is made of polymer matrix (polyethylene glycol (PEG) and ethylene-vinyl acetate (EVA)) and conductive ingredient (high structured carbon black nanoparticles). Used polymer matrixes differ with structure and polarity. PEG is highly crystalline and polar polymer, while EVA has amorphous structure and is non-polar polymer. Specifically formed sensor material structure enables chemical vapour detection in the air. PEG-NCC and EVA-NCC percolation thresholds are determined. PEG-NCC percolation curve shows unexpected behavior, instead of one percolation threshold we observed two thresholds at 3 and 8 mass parts of carbon black. EVA-NCC percolation threshold is around 7 mass parts of carbon black. Conclusion is that linear polymer macromolecules, like PEG have, promoted faster conductive channel formation between carbon black nanopartilces. PEG-NCC and EVA-NCC chemical vapour sensitivity depending on concentration of carbon black have been evaluated. As expected both composites show the best ethanol vapour sensitivity slightly above percolation thresholds. PEG-NCC highest response is observed at 8 mass parts of carbon black. It can be explained with PEG crystalline structure reduction when increase the concentration of carbon black in the composite content
Recently we have elaborated polyisoprene/high structured carbon black composites with excellent p... more Recently we have elaborated polyisoprene/high structured carbon black composites with excellent piezoresistivity effect as well as chemoresistivity effect. The task of this study is to test the thermoexfoliated graphite (TEG) as well as multiwall carbon nanotubes (with high (LMWCNT) and low (SMWCNT) aspect ratio) for their application in design of new sensitive polymer composites. TEG has been synthesized in Department of Physics of KNTSU. Polyisoprene/TEG and polyisoprene /MWCNT composites were prepared in Institute of Technical Physics of RTU. Piezoresistivity and chemoresitivity DC and AC tests of composites show promising results. Polyisoprene/TEG composite has higher sensitivity to chemicals then polyisoprene/LMWCNT. It allows to expect all the better sensitivity of polymer/single graphene composites in future
black composites we can achieve excellent piezoresistivity effect [1] as well as chemoresistivity... more black composites we can achieve excellent piezoresistivity effect [1] as well as chemoresistivity effect [2] for these composites. In this study we attempt to design polyisoprene matrix composites with promising more sophisticated fillers – thermoexfoliated graphite (TEG) as well as multiwall carbon nanotubes with high (LMWCNT) and low (SMWCNT) aspect ratio for their application in design of new sensitive polymer composites. TEG has been synthesized in Department of Physics of Kyiv National Taras Shevchenko University. Powders of LMWCNT and SMWCNT have been bought from Cheap Tubes Inc. Polyisoprene/TEG and polyisoprene /MWCNT composites were prepared in Institute of Technical Physics of Riga Technical University. Firstly each filler party was dispersed in chloroform in one vessel by ultrasonic homogenizer. Secondly polyisoprene and necessary additives, zinc oxide and sulphur were dissolved in chloroform in another vessel by magnetic stirring. After the definite filler dispersion was added to polyisoprene solution and the mixture was mixed by magnetic stirring for 24 hours. From the obtained raw mixture chloroform was evaporated. Finally the mixture was vulcanized under pressure of 30 atm at 150oC for 15 minutes. The acquired nanocomposite samples were electrically conductive and showed the ability to change the electrical resistance under the influence of mechanical force and volatile compound vapours as well
ABSTRACT Carbon nanomaterials (CNM) and molybdenum compound nanostructures are materials with var... more ABSTRACT Carbon nanomaterials (CNM) and molybdenum compound nanostructures are materials with various applications yet little is known regarding the toxicity of these nanoparticles in pristine form in aquatic environment. Daphnia magna standard acute toxicity test (EN ISO 6341:1996; freshwater) and Artemia salina standard acute toxicity test (ArtoxKit standard method; 15 ppt saltwater) were applied to assess the toxicity of non-modified CNM and molybdenum compound nanowires in water. It has been observed that CNM are more toxic in freshwater suspensions and somewhat more toxic than the tested molybdenum compound nanowires.
The aim of this work is to investigate chemo-resistivity properties of natural rubber-carbon nano... more The aim of this work is to investigate chemo-resistivity properties of natural rubber-carbon nanostructure composite, that’s why a change of diffusion characteristics and reversibility of electro-chemical properties of the composite with different degree values of crosslinks have been analysed. The composites are made from natural rubber (polyisoprene) as matrix material and high structure carbon black as electro-conductive filler. In order to investigate diffusion characteristics of volatile organic compounds (VOC) in relation to chemo-resistive response of composites simultaneous mass, length and electrical resistance change measurements of the samples, when samples are held in VOC and after exposures to VOC were carried out. Electrical resistance increase mechanism in the composite advances with the composite structure development during vulcanization.
We are presenting highly porous ethyl cellulose (EC) nanostructured films for triboelectric nanog... more We are presenting highly porous ethyl cellulose (EC) nanostructured films for triboelectric nanogenerator (TENG) contact layer material with high performance for converting mechanical energy to electricity. Homogeneous porous EC films were deposited on conductive substrate in less than one minute without need for specific equipment. EC triboelectric layer material was contacted with tin doped In 2 O 3 , polydimethylsiloxane (PDMS) and polymethyl methacrylate. In system where EC was contacted against PDMS three orders of magnitude higher power density was observed comparing to other systems, demonstrating that prepared EC is a superior triboelectric layer material for using in TENG devices in conjunction with PDMS.
In order to acquire a flexible resistive heating element in the temperature range for human body ... more In order to acquire a flexible resistive heating element in the temperature range for human body heating, the influence of DC voltage on chloroprene rubber (CR) and carbon black (CB) composites has been investigated. Three conduction mechanisms have been found to occur in the range from 0.5 V to 10 Vcharge velocity increase due to the increase of the electric field, matrix thermal expansion that results in decreased tunnelling currents and new electroconductive channel formation at voltages above 7.5 V, where the temperature exceeds the matrix's softening point. As opposed to external heating, during resistive heating, the composite exhibits a negative temperature coefficient of resistivity up to an applied voltage of 5 V. The intrinsic electro-chemical matrix properties play an important role in the overall resistivity of the composite. The material shows cyclical stability when repeatedly applying a voltage of 5 V and can be used as a human body heating element.
In this work the improvement of an efficiency of electrostatic harvesters by using polymer/nanost... more In this work the improvement of an efficiency of electrostatic harvesters by using polymer/nanostructured carbon composites (PNC) is investigated. In electrostatic harvesters the energy of mechanical oscillations is conversed into electrical energy through deformation of an insulator (dielectric) layer between plates of a charged capacitor. To increase the change of voltage during the deformation of dielectric layer between capacitor plates, its dielectric permittivity should decrease with tensile deformation. Capacitor samples containing PNC dielectric layer were elaborated from polyisoprene, electroconductive carbon nanoparticles and brass electrodes.Tensile and compressive deformation measurements conducted on PNC samples showed, that under tensile and compressive deformation dielectric permittivity of the PNC composite is decreasing. It was also found, that the character of dielectric permittivity changes for both - tensile and compressive deformation - is different. The change of dielectric properties observed indicates about complex processes taking place in the PNC dielectric layer
Vērtēti izveidotie un Blackboard vidē ievietotie multimēdiju studiju materiāli Fizikā Tehniskās U... more Vērtēti izveidotie un Blackboard vidē ievietotie multimēdiju studiju materiāli Fizikā Tehniskās Unicersitātes studentiem. Analizēta sakarība starp to, cik aktīvi students iznamtojis materiālus, un iegūto eksāmena vērtējumu.Viena gada rezultātu analīze rāda, ka galvenokārt vērtējums ir atkarīgs no kontaktstundu skaita, nevis no e-studiju materiālu lietošanas intensitātes. Multimēdiju materiāli galvenokārt kalpo kā papildinājums studijām ārpus kontaktstundām
Two types of polymer - nanostructured carbon composites were made. Both samples were exposed to e... more Two types of polymer - nanostructured carbon composites were made. Both samples were exposed to ethanol vapours and shows repeatable sensoreffect. Additionaly composite with carbon nanoparticles (EVA-CB), where exposed to fuel vapour. It was found that EVA-CB is able to distinguish different oil based products – petrol (with octane number 95) an diesel. When EVA-CB was exposed to petrol vapour, the composite relative electric resistance change was much larger comaring to diesel vapour. Observed difference in the composite response is explained by volatiliy of different fuel type
Fluctuation in the surface irregularities is found to be the reason for surface charge formation ... more Fluctuation in the surface irregularities is found to be the reason for surface charge formation by contacting two identical polymers. Higher surface charge is shown to correlate with higher disparity in porosity or surface roughness.
Recent achievements of scientific group of Riga Technical University in collaboration with COINAP... more Recent achievements of scientific group of Riga Technical University in collaboration with COINAPO partners in design, processing and investigation of polyisoprene composites with conductive tubular nanostructures (PCCTN) as prospective materials for completely hyper-elastic (non-rigid) mechanical (pressure, strain) indicators, chemical vapour indicators as well as temperature indicators have been presented. Non-rigid multifunctional sensing materials attract attention of scientists and engineers because of potential possibility to incorporate them in different solid and nonsolid systems for specific parameter control. Previous experience with electro-active materials like ferroelectrics suggests that maximum sensitivity of material to any influence is observed in the vicinity of phase transitions. The percolation transition in PCCTN could be imagined as specific phase transition from electrically insulating state to electrically conductive state. Thus, the maximum sensitivity of PCCTN materials to external thermodynamic forces (ETF) should be expected in the vicinity of percolation threshold. The reversibility of material reaction to ETF should be achieved by positioning conductive tubular nanostructures in the spatial grid by curing of hyper-elastic polymer matrix. Our previous research approved that high structure carbon black PRINTEX XE2 filled composites demonstrate finger pressure sensitive piezoresistivity as well as good organic solvent vapour sensing. Conductive tubular nanostructures originate with variable length to width ratio and high electric conductivity in longitudinal direction of the tubes, which theoretically should make it possible to obtain electric percolation in polymercarbon nanotube composites at very low loads of filler. However recent experience with mechanically dispersed carbon nanotubes shows quite high values of percolation threshold and specific sensing properties. In this work we present an attempt to use ultrasound for improved dispersion of the filler in polyisoprene matrix composite. Multi wall carbon nanotubes (MWCNT) “Aldrich 636835” as well as inorganic nanotubules (IN) Mo6S2I8 and MoO3-X are used as filler. As reference filler PRINTEX XE2 was also used. The noticeable shifting of percolation threshold to lower values of concentration has been achieved for all types of nano-composites. The piezoresistive and chemosensitive behaviour of sonicated nano-composites have been determined and compared with mechanically mixed ones. The obtained results are explained using quantum mechanical charge tunnelling and percolation theory
We investigated a promising material for hydrogen storage and sensing. The material was obtained ... more We investigated a promising material for hydrogen storage and sensing. The material was obtained by exfoliating recycled graphite waste and simultaneously modifying the product with metal impurities (Bi, V, Cu). As a result, graphene sheet stack (GSS) powder was obtained. The material was further processed by hydrothermal annealing and reduction. Raman spectra of the GSS materials are provided to show the presence of graphene-like structures and defects in the exfoliated material. The synthesized graphene material has good semiconductor properties with a low electrical resistance for hydrogen sensing applications.
Nowadays scientific progress and improving of chemical industry has made a big step forward. That... more Nowadays scientific progress and improving of chemical industry has made a big step forward. That means, the possibility of various organic solvents to come in tracheas of workers is growing and it can make irreversible damage to workers organism. Therefore there is a need to design, elaborate and investigate polymer-nanostructured carbon composite (P-NCC), which would serve in factories as a sensor material and would warn workers about health risks or it can help manufacturers control production processes. Sensor material is made of polymer matrix (polyethylene glycol (PEG) and ethylene-vinyl acetate (EVA)) and conductive ingredient (high structured carbon black nanoparticles). Used polymer matrixes differ with structure and polarity. PEG is highly crystalline and polar polymer, while EVA has amorphous structure and is non-polar polymer. Specifically formed sensor material structure enables chemical vapour detection in the air. PEG-NCC and EVA-NCC percolation thresholds are determined. PEG-NCC percolation curve shows unexpected behavior, instead of one percolation threshold we observed two thresholds at 3 and 8 mass parts of carbon black. EVA-NCC percolation threshold is around 7 mass parts of carbon black. Conclusion is that linear polymer macromolecules, like PEG have, promoted faster conductive channel formation between carbon black nanopartilces. PEG-NCC and EVA-NCC chemical vapour sensitivity depending on concentration of carbon black have been evaluated. As expected both composites show the best ethanol vapour sensitivity slightly above percolation thresholds. PEG-NCC highest response is observed at 8 mass parts of carbon black. It can be explained with PEG crystalline structure reduction when increase the concentration of carbon black in the composite content
Recently we have elaborated polyisoprene/high structured carbon black composites with excellent p... more Recently we have elaborated polyisoprene/high structured carbon black composites with excellent piezoresistivity effect as well as chemoresistivity effect. The task of this study is to test the thermoexfoliated graphite (TEG) as well as multiwall carbon nanotubes (with high (LMWCNT) and low (SMWCNT) aspect ratio) for their application in design of new sensitive polymer composites. TEG has been synthesized in Department of Physics of KNTSU. Polyisoprene/TEG and polyisoprene /MWCNT composites were prepared in Institute of Technical Physics of RTU. Piezoresistivity and chemoresitivity DC and AC tests of composites show promising results. Polyisoprene/TEG composite has higher sensitivity to chemicals then polyisoprene/LMWCNT. It allows to expect all the better sensitivity of polymer/single graphene composites in future
black composites we can achieve excellent piezoresistivity effect [1] as well as chemoresistivity... more black composites we can achieve excellent piezoresistivity effect [1] as well as chemoresistivity effect [2] for these composites. In this study we attempt to design polyisoprene matrix composites with promising more sophisticated fillers – thermoexfoliated graphite (TEG) as well as multiwall carbon nanotubes with high (LMWCNT) and low (SMWCNT) aspect ratio for their application in design of new sensitive polymer composites. TEG has been synthesized in Department of Physics of Kyiv National Taras Shevchenko University. Powders of LMWCNT and SMWCNT have been bought from Cheap Tubes Inc. Polyisoprene/TEG and polyisoprene /MWCNT composites were prepared in Institute of Technical Physics of Riga Technical University. Firstly each filler party was dispersed in chloroform in one vessel by ultrasonic homogenizer. Secondly polyisoprene and necessary additives, zinc oxide and sulphur were dissolved in chloroform in another vessel by magnetic stirring. After the definite filler dispersion was added to polyisoprene solution and the mixture was mixed by magnetic stirring for 24 hours. From the obtained raw mixture chloroform was evaporated. Finally the mixture was vulcanized under pressure of 30 atm at 150oC for 15 minutes. The acquired nanocomposite samples were electrically conductive and showed the ability to change the electrical resistance under the influence of mechanical force and volatile compound vapours as well
ABSTRACT Carbon nanomaterials (CNM) and molybdenum compound nanostructures are materials with var... more ABSTRACT Carbon nanomaterials (CNM) and molybdenum compound nanostructures are materials with various applications yet little is known regarding the toxicity of these nanoparticles in pristine form in aquatic environment. Daphnia magna standard acute toxicity test (EN ISO 6341:1996; freshwater) and Artemia salina standard acute toxicity test (ArtoxKit standard method; 15 ppt saltwater) were applied to assess the toxicity of non-modified CNM and molybdenum compound nanowires in water. It has been observed that CNM are more toxic in freshwater suspensions and somewhat more toxic than the tested molybdenum compound nanowires.
The aim of this work is to investigate chemo-resistivity properties of natural rubber-carbon nano... more The aim of this work is to investigate chemo-resistivity properties of natural rubber-carbon nanostructure composite, that’s why a change of diffusion characteristics and reversibility of electro-chemical properties of the composite with different degree values of crosslinks have been analysed. The composites are made from natural rubber (polyisoprene) as matrix material and high structure carbon black as electro-conductive filler. In order to investigate diffusion characteristics of volatile organic compounds (VOC) in relation to chemo-resistive response of composites simultaneous mass, length and electrical resistance change measurements of the samples, when samples are held in VOC and after exposures to VOC were carried out. Electrical resistance increase mechanism in the composite advances with the composite structure development during vulcanization.
We are presenting highly porous ethyl cellulose (EC) nanostructured films for triboelectric nanog... more We are presenting highly porous ethyl cellulose (EC) nanostructured films for triboelectric nanogenerator (TENG) contact layer material with high performance for converting mechanical energy to electricity. Homogeneous porous EC films were deposited on conductive substrate in less than one minute without need for specific equipment. EC triboelectric layer material was contacted with tin doped In 2 O 3 , polydimethylsiloxane (PDMS) and polymethyl methacrylate. In system where EC was contacted against PDMS three orders of magnitude higher power density was observed comparing to other systems, demonstrating that prepared EC is a superior triboelectric layer material for using in TENG devices in conjunction with PDMS.
In order to acquire a flexible resistive heating element in the temperature range for human body ... more In order to acquire a flexible resistive heating element in the temperature range for human body heating, the influence of DC voltage on chloroprene rubber (CR) and carbon black (CB) composites has been investigated. Three conduction mechanisms have been found to occur in the range from 0.5 V to 10 Vcharge velocity increase due to the increase of the electric field, matrix thermal expansion that results in decreased tunnelling currents and new electroconductive channel formation at voltages above 7.5 V, where the temperature exceeds the matrix's softening point. As opposed to external heating, during resistive heating, the composite exhibits a negative temperature coefficient of resistivity up to an applied voltage of 5 V. The intrinsic electro-chemical matrix properties play an important role in the overall resistivity of the composite. The material shows cyclical stability when repeatedly applying a voltage of 5 V and can be used as a human body heating element.
In this work the improvement of an efficiency of electrostatic harvesters by using polymer/nanost... more In this work the improvement of an efficiency of electrostatic harvesters by using polymer/nanostructured carbon composites (PNC) is investigated. In electrostatic harvesters the energy of mechanical oscillations is conversed into electrical energy through deformation of an insulator (dielectric) layer between plates of a charged capacitor. To increase the change of voltage during the deformation of dielectric layer between capacitor plates, its dielectric permittivity should decrease with tensile deformation. Capacitor samples containing PNC dielectric layer were elaborated from polyisoprene, electroconductive carbon nanoparticles and brass electrodes.Tensile and compressive deformation measurements conducted on PNC samples showed, that under tensile and compressive deformation dielectric permittivity of the PNC composite is decreasing. It was also found, that the character of dielectric permittivity changes for both - tensile and compressive deformation - is different. The change of dielectric properties observed indicates about complex processes taking place in the PNC dielectric layer
Vērtēti izveidotie un Blackboard vidē ievietotie multimēdiju studiju materiāli Fizikā Tehniskās U... more Vērtēti izveidotie un Blackboard vidē ievietotie multimēdiju studiju materiāli Fizikā Tehniskās Unicersitātes studentiem. Analizēta sakarība starp to, cik aktīvi students iznamtojis materiālus, un iegūto eksāmena vērtējumu.Viena gada rezultātu analīze rāda, ka galvenokārt vērtējums ir atkarīgs no kontaktstundu skaita, nevis no e-studiju materiālu lietošanas intensitātes. Multimēdiju materiāli galvenokārt kalpo kā papildinājums studijām ārpus kontaktstundām
Two types of polymer - nanostructured carbon composites were made. Both samples were exposed to e... more Two types of polymer - nanostructured carbon composites were made. Both samples were exposed to ethanol vapours and shows repeatable sensoreffect. Additionaly composite with carbon nanoparticles (EVA-CB), where exposed to fuel vapour. It was found that EVA-CB is able to distinguish different oil based products – petrol (with octane number 95) an diesel. When EVA-CB was exposed to petrol vapour, the composite relative electric resistance change was much larger comaring to diesel vapour. Observed difference in the composite response is explained by volatiliy of different fuel type
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