Maria Omastova | Slovak Academy of Sciences (original) (raw)
Papers by Maria Omastova
Smart Materials and Structures, Sep 19, 2013
ABSTRACT The photo-actuation behavior of nanocomposites based on ethylene–vinylacetate copolymer ... more ABSTRACT The photo-actuation behavior of nanocomposites based on ethylene–vinylacetate copolymer (EVA) and styrene–isoprene–styrene (SIS) block copolymer filled with well-dispersed and modified multiwalled carbon nanotubes (MWCNTs) is discussed in this paper. The nanocomposites were prepared by casting from solution. To improve the dispersion of the MWCNTs in EVA, the MWCNT surface was modified with a non-covalent surfactant, cholesteryl 1-pyrenecarboxylate (PyChol). To prepare SIS nanocomposites, the MWCNT surface was covalently modified with polystyrene chains. The good dispersion of the filler was confirmed by transmission electron microscopy (TEM). Special, custom-made punch/die molds were used to create a Braille element (BE)-like shape, which under shear forces induces a uniaxial orientation of the MWCNTs within the matrix. The uniaxial orientation of MWCNTs is an essential precondition to ensure the photo-actuating behavior of MWCNTs in polymeric matrices. The orientation of the MWCNTs within the matrices was examined by scanning electron microscopy (SEM). Nanocomposite BEs were illuminated from the bottom by a red light-emitting diode (LED), and the photo-actuation was investigated by confocal laser scanning microscopy (CLSM). When the BEs were exposed to light, a temporary increase in the height of the element was detected. This process was observed to be reversible: after switching off the light, the BEs returned to their original shape and height.
Composites Part A-applied Science and Manufacturing, Mar 1, 2016
This study aims to investigate experimentally the effects of aspect ratio (length/diameter ratio)... more This study aims to investigate experimentally the effects of aspect ratio (length/diameter ratio) and concentration of multiwalled carbon nanotubes (MWCNTs) on thermal properties of high density polyethylene (HDPE) based composites. The aspect ratios of two types of MWCNT fillers are in the range of 200-400 and 500-3000. Composite samples were prepared by melt mixing up to weight fraction of 19% filler content, followed by a compression molding. Measurements of density, specific heat and thermal diffusivity (by modulated photothermal radiometry, PTR) were performed and effective thermal conductivities k e of nanocomposites were calculated using these values. The results show that the composites containing MWCNTs with higher aspect ratio have higher thermal conductivities than the ones with lower aspect ratio. In terms of conductivity enhancement k e /k m À 1, the results indicate that MWCNTs with higher aspect ratio provide three to fourfold larger enhancement than the ones with lower aspect ratio, at low filler concentrations.
Archives of materials science and engineering, 2008
Hybrid ethylene-propylene-diene-monomer (EPDM) nanocomposite foams were produced via compression ... more Hybrid ethylene-propylene-diene-monomer (EPDM) nanocomposite foams were produced via compression molding with enhanced electromagnetic wave absorption efficiency. The hybrid filler, consisting of 20 phr ferroelectric barium titanate (BT) and various loading fractions of multi-wall carbon nanotubes (MWCNTs), synergistically increased the electromagnetic (EM) wave absorption characteristics of the EPDM foam. Accordingly, while the EPDM foam filled with 20 phr BT was transparent to the EM wave within the frequency range of 8.2-12.4 GHz (X-band), the hybrid EPDM nanocomposite foam loaded with 20 phr BT and 10 phr MWCNTs presented a total shielding effectiveness (SE) of~22.3 dB compared to~16.0 dB of the MWCNTs (10 phr). This synergistic effect is suggested to be due to the segregation of MWCNT networks within the cellular structure of EPDM, resulting in enhanced electrical conductivity, and also high dielectric permittivity of the foam imparted by the BT particles. Moreover, the total SE of the BT/MWCNTs loaded foam samples remained almost unchanged when subjected to repeated bending due to the elastic recovery behavior of the crosslinked EPDM foamed nanocomposites.
Mikrochimica Acta, Dec 17, 2019
An electrochemical study was performed on the behavior of Ti 3 C 2 T x MXenes prepared by using e... more An electrochemical study was performed on the behavior of Ti 3 C 2 T x MXenes prepared by using either HF (MXene1) or LiF/HCl as etchants (MXene2). The use of two redox probes indicates the presence of a higher negative charge density on MXene2 in comparison to MXene1. The characterization of two nanomaterials shows that titanium and fluoride are present higher by one order of magnitude at the interface of MXene2, compared to MXene1. The high Ti and F content is accompanied by a 82-fold larger (249 μA•cm −2 vs. 5.64 μA•cm −2) anodic peak at the peak potential near 0.4 V (vs. Ag/AgCl). Similarly, the peak current on MXene2 is 317-fold higher for the oxygen reduction at pH 7.0 (at a voltage of −0.84 V) and 215-fold higher for the reduction of H 2 O 2 at −0.89 V, when compared to MXene1. Keywords MXene. Ti 3 C 2 T X. Electrocatalysis. Electrochemistry. H 2 O 2 reduction. Oxygenreduction reactions. Redox stability
Composites Part B-engineering, Oct 1, 2013
High-density polyethylene (HDPE) was reinforced with expanded and untreated graphite in a meltcom... more High-density polyethylene (HDPE) was reinforced with expanded and untreated graphite in a meltcompounding process. Viscosity increased upon addition of graphite phase, with the expanded graphite (EG) showing more dramatic rise than the untreated graphite (UG) in viscosity. The increase in viscosity was attributed to the increased surface-to-volume ratio for the EG filler after acid treatment. Electrical conductivity also increased from that pertaining to an insulator to one characteristic of a semiconductor. The EG system showed a lower percolation threshold for transition in conductivity compared to that in the UG system. DSC results indicated that the fillers acted as a nucleating agent in inducing the crystallization of HDPE in the composites. However, the overall degree of crystallinity and melting temperature of HDPE decreased with the addition of EG and UG. Mechanical properties improved as a function of filler content but the overall enhancement was not impressive. It was conjectured that the filler-matrix interface was not optimized in the melt-mixing process. However, the role of EG as a reinforcement phase for both electrical and mechanical properties was unambiguously established. The EG composites demonstrated potentially useful attributes for antistatic, barrier, mechanical, electrical, and cost-effective applications.
Procedia Engineering, 2015
In polymer composites and nanocomposites with conducting fillers, conductivity changes significan... more In polymer composites and nanocomposites with conducting fillers, conductivity changes significantly with strain and with the evolution of damage, which forms the basis for using the composite itself as sensor (self-sensing) for strain and for structural health monitoring. Less frequent is the use of capacitance sensors, where the changes of capacitance of the sample during deformation are utilized. Here we present results of recent work in the use of electrical dc measurements to monitor strain and to follow the onset and evolution of damage in selected examples of polymer composites and nanocomposites, pointing out differences in their properties. The materials we measured were PP (Poly-Propylene) filled with unfunctionalized MWCNTs (Multi Walled Carbon Nano-Tubes), SBR (Styrene Butadiene Rubber) filled with CB (Carbon Black) and PEEK (Poly-Ether-Ether-Ketone) reinforced with CFs (Carbon Fibers).
Polymer Engineering and Science, 2007
Novel silicon carbide/polypyrrole (SiC/PPy) conducting composites were prepared using silicon car... more Novel silicon carbide/polypyrrole (SiC/PPy) conducting composites were prepared using silicon carbide as inorganic substrate in the presence or absence of an anionic surfactant, dodecylbenzenesulfonic acid (DBSA). The surface modification of SiC particles was performed in aqueous solution containing the anionic surfactant by oxidative polymerization of pyrrole using ferric chloride as oxidant. Ash content analysis was used to determine the mass loading of organic fraction in the SiC/PPy composites. Scanning electron microscopy showed the surface modification of SiC by PPy. The presence of PPy in the composites was confirmed by infrared spectroscopy. The small gradual red shift of the band of the stretching vibrations of SiCO and SiOSi bonds and more intensive of PPy spectrum were observed when DBSA was used for composite preparation. The presence of both polypyrrole and surfactant was also detected by their respective N1s and S2p core level peaks recorded by X‐ray photoelectron spectroscopy. The electrical conductivity of SiC‐DBSA/PPy composites depends on PPy content at the surface and on pyrrole/DBSA molar ratio. The DBSA‐containing composites have a conductivity about 2 orders of magnitude higher than in the case of the composites prepared without DBSA when PPy loading was lower than 15 wt%. Above this PPy loading the difference in conductivity almost diminished due to a increased amount of PPy polymerized on the surface of the SiC substrate. SiC‐DBSA/PPy composites containing 15 wt% PPy prepared using a molar ratio pyrrole/DBSA = 5, exhibited a very hydrophobic behavior compared to the corresponding DBSA‐free composites, as they floated on water and did not sediment even after a prolonged period of time. POLYM. ENG. SCI., 47:1198–1206, 2007. © 2007 Society of Plastics Engineers
Journal of Nanophotonics, Oct 17, 2012
Abstract. The photo-actuating behavior of new polymeric nanocomposite materials based on a commer... more Abstract. The photo-actuating behavior of new polymeric nanocomposite materials based on a commercial elastomer, an ethylene-vinylacetate copolymer (EVA), filled with multiwalled carbon nanotubes (MWCNT) was investigated. A good dispersion of the MWCNT within the elastomeric matrix was ensured by using a novel, specific compatibilizer consisting of pyrenyl and cholesteryl groups. A uniaxial orientation of the MWCNT within the matrix was induced with shear forces by employing a special custom-made punch/die system. Good dispergation and alignment of the MWCNT within the matrix were demonstrated by scanning electron microscopy. Transmission electron microscopy showed a good dispersion of the MWCNT within the composite. Photo-actuation was qualitatively characterized by atomic force microscopy and quantitatively characterized by nanoindentation. The samples prepared in the form of Braille element showed expansion upon illumination by light diodes. The maximal height deformation changes about 15% was detected when a blue diode was used.
Materials Research Bulletin, May 1, 2005
Novel silicon carbide/polypyrrole (SiC/PPy) conducting composites were prepared using silicon car... more Novel silicon carbide/polypyrrole (SiC/PPy) conducting composites were prepared using silicon carbide as inorganic substrate. The surface modification of SiC was performed in aqueous solution by oxidative polymerization of pyrrole using ferric chloride as oxidant. Elemental analysis was used to determine the mass loading of polypyrrole in the SiC/PPy composites. Scanning electron microscopy showed the surface modification of SiC by PPy. PPy in composites was confirmed by the presence of PPy bands in the infrared spectra of SiC/PPy containing various amounts of conducting polymer. The conductivity of SiC/PPy composites depends on PPy content on the surface. The composite containing 35 wt.% PPy showed conductivity about 2 S cm À1 , which is in the same range as the conductivity of pure polypyrrole powder prepared under the same conditions using the same oxidant. PPy in the composites was clearly detected by X-ray photoelectron spectroscopy (XPS) measurements by its N1s and Cl2p peaks. High resolution scans of the C1s regions distinguished between silicon carbide and polypyrrole carbons. The fraction of polypyrrole at the composite surface was estimated from the silicon and nitrogen levels. The combination of XPS and conductivity measurements suggests that the surface of the SiC/PPy composites is polypyrrole-rich for a conducting polymer mass loading of at least 12.6 wt.%.
Polymer Degradation and Stability, 2003
The electrical properties of polymer composites-polyethylene/carbon black (PE/CB), polyethylene/c... more The electrical properties of polymer composites-polyethylene/carbon black (PE/CB), polyethylene/carbon black modified by polypyrrole (PE/CB-PPy), and polyethylene/carbon black modified by polyaniline (PE/CB-PANI)-were investigated during slow cyclic heating and cooling thermal ageing. Conductivity in composites was measured in heating/cooling cycles in the temperature range from 16 to 125 C. Scanning electron microscopy was used for morphology study of surface of modified CB particles. It was found that the thermal treatment resulted in a conductivity increase in all composites when heated below the melting point of PE. This effect was explained by increased crystallinity in the polymer matrix of thermally treated composites and confirmed by DSC analysis. The thermal ageing during the heating above the melting point of polymer matrix caused decrease in conductivity of PE/ CB composites, but increase of conductivity in composites containing CB-PPy or CB-PANI as a filler. The modified fillers create more perfect and thermally resistant conducting network in PE matrix. The temperature of decomposition maximum of PE/CB-PPy and PE/CB-PANI composites into higher compared with PE/CB composite as observed by thermogravimetric analysis.
Synthetic Metals, Apr 1, 2010
The conducting polymers, polypyrrole and polyaniline, were synthesized by chemical oxidative poly... more The conducting polymers, polypyrrole and polyaniline, were synthesized by chemical oxidative polymerization of the corresponding monomers in 0.1 M sulfuric acid using cerium(IV) sulfate as the oxidant at mole ratios of oxidant-to-monomer ranging from 0.5 to 3. The yields of the oxidation products were determined, and the samples were characterized with respect to their elemental composition, molecular structure, and morphology. The conductivity of polypyrrole prepared in 0.1 M sulfuric acid, 10 −1 to 10 0 S cm −1 , was higher compared with the conductivity of polyaniline prepared under the same conditions, 10 −3 to 10 −1 S cm −1. The loss of mass after deprotonation with ammonium hydroxide is reported, and discussed in terms of the type of protonation as also reflected by FTIR spectroscopy. The conductivity of polypyrrole bases remained at relatively high level, 10 −5 to 10 −3 S cm −1 , while PANI bases became non-conducting, 10 −12 to 10 −10 S cm −1. The polymers had a granular morphology in all cases.
Synthetic Metals, Jul 1, 2003
Conducting and stable polypyrrole (PPy) was synthesized by chemical oxidative polymerization of p... more Conducting and stable polypyrrole (PPy) was synthesized by chemical oxidative polymerization of pyrrole in aqueous solution containing an oxidant, ferric sulfate, and a surfactant. Anionic surfactants: sodium dodecylbenzenesulfonate, dodecylbenzenesulfonic acid, sodium dodecyl sulfate, poly(ethylene oxide)-n-alkyl-3-sulfopropyl ether potassium salt; cationic surfactant: tetradecyltrimethylammonium bromide; and non-ionic surfactants: poly(ethylene oxide) (10) iso-octylphenyl ether (Triton 1 X-100), poly(ethylene oxide) (20) sorbitan monolaurate (Tween 1 20) and poly(ethylene oxide) (20) sorbitan monostearate (Tween 1 60) were used as additives. Results of the elemental analysis and FTIR spectroscopy proved that only the anionic surfactants were incorporated into PPy similarly as the doping anion. This leads to a better stability towards the deprotonation. Also thermal stability, checked by TGA in air, was improved. Scanning electron microscopy studies showed that the presence of the anionic surfactant strongly influenced the morphology of the polymer product.
Nanotechnology, May 10, 2021
High-density polyethylene (HDPE)-based hybrid nanocomposites containing graphene nanoplatelets (G... more High-density polyethylene (HDPE)-based hybrid nanocomposites containing graphene nanoplatelets (GnPs) and multiwall carbon nanotubes (MWCNTs) were fabricated using melt mixing followed by compression molding. The influences of size and weight ratio of both carbon-based nanofillers on the electrical, thermal, and mechanical properties of hybrid nanocomposites were evaluated. This study proves that the size and weight ratio of carbon-based nanofillers play a critical role in determining these properties. The optimum size and weight ratio of GnPs and MWCNTs are determined at the maximum achieved enhancement for each property. The HDPE-based nanocomposites containing GnPs with larger surface area and MWCNTs with higher aspect ratio display the highest electrical conductivity at GnPs/MWCNTs weight ratio of 2/3. The combination of GnPs with larger surface area and MWCNTs with lower aspect ratio provides the maximum Young’s modulus enhancement of hybrid nanocomposites at 1/4 weight ratio of GnPs and MWCNTs. The nanocomposite containing GnPs with the largest lateral size and MWCNTs with a higher aspect ratio at a 3/2 weight ratio exhibits the highest thermal conductivity. Also, at around the percolation threshold of GnPs, the incorporation of MWCNTs with larger aspect ratio into the HDPE-based nanocomposites containing GnPs with the largest lateral size shows a distinct synergic effect on the thermal conductivity and Young’s modulus, while an additive effect on the electrical conductivity and thermal stability.
Proceedings of SPIE, Sep 8, 2011
Photomechanical actuation is preferred to electromechanical transduction because of some advantag... more Photomechanical actuation is preferred to electromechanical transduction because of some advantages including wireless connection, a producing low noise, fast response etc. However, only few materials actually exhibit photoactuation. Recently, nanotube-enriched elastomeric polymers have shown photo-actuating properties; the best results were reported for liquid crystals elastomers. In the present paper we discuss photo-actuating behavior of new photoactuating materials based on the
Materials, Sep 15, 2018
The electrospinning of an ethylene vinyl acetate (EVA) copolymer with a vinyl acetate content of ... more The electrospinning of an ethylene vinyl acetate (EVA) copolymer with a vinyl acetate content of 28 wt.% is limited due to the solubility of the copolymer in standard laboratory conditions. Poly(lactic acid) (PLA) is a biodegradable polymer that can be electrospun easily. However, PLA has limited applicability because it is brittle. Blends of these polymers are of interest in order to obtain new types of materials with counterbalanced properties originating from both polymeric compounds. The fibers were electrospun on a water surface from a solution mixture containing various weight ratios of both polymers using a dichloromethane and acetone (70:30 v/v) mixture as solvent. The morphologies of the prepared non-woven mats were examined by scanning electron microscopy (SEM), and the chemical composition was investigated by X-ray photoelectron spectroscopy (XPS) and by Fourier Transform Infrared Spectroscopy (FTIR). The fibers' thermal properties and stability were examined, and the mechanical properties were tested. The results showed that the strength and flexibility of the blend samples were enhanced by the presence of PLA.
International Journal of Thermal Sciences, Dec 1, 2012
This work aimed at thermal transport characterization of high density polyethylene (HDPE) filled ... more This work aimed at thermal transport characterization of high density polyethylene (HDPE) filled with 5 and 50 mm expanded graphite (EG) particles and with 0.4 mm unexpanded graphite (UG) particles. Sample platelets were produced by melt mixing followed by compression molding. Thermal conductivity k was determined by combining measurements of density, specific heat capacity and thermal diffusivity, the latter by modulated photothermal radiometry (PTR). Starting from an effective medium approximation model, we derived a linearized expression for the effective k of composites with low particle charge. It explains the unusually high experimental k values (up to four-fold increase) as the effect of strongly non-spherical EG particles (aspect ratio 1/p ¼ 110e290). Larger particle sizes produce higher k enhancement, while the interfacial thermal resistance (R bd ¼ 2.1,10 À7 m 2 ,K/W) has an opposite effect. The same model is consistent with experimental k for low particle charge HDPE/UG composites. At higher particle charge the model fails due to particle interaction leading to validity break of the effective medium approximation.
Materials Research Express, 2019
The effects of the aspect ratio and the addition of multiwall carbon nanotubes (MWCNTs) on the mo... more The effects of the aspect ratio and the addition of multiwall carbon nanotubes (MWCNTs) on the morphological, electrical, mechanical and thermal properties of high-density polyethylene (HDPE)-based nanocomposites are investigated. The HDPE nanocomposites with various amounts up to 18.74 wt.% of MWCNTs that have two different aspect ratios (AR), (200–400(M58) and 500–3000(M12)) were prepared by a melt mixing method, followed by compression molding. The results demonstrate that the addition of MWCNTs enhances the electrical, mechanical and thermal properties of the HDPE/MWCNTs nanocomposites. The HDPE nanocomposites with higher aspect ratio MWCNTs demonstrated a slightly better enhancement in the morphological and electrical properties than the other ones with lower aspect ratio MWCNTs. Additionally, Young's modulus and the thermal stability increased with increasing aspect ratio of MWCNTs.
Applied Surface Science, 2019
A conducting polymer, polypyrrole, was deposited on tungsten disulfide flakes in situ during the ... more A conducting polymer, polypyrrole, was deposited on tungsten disulfide flakes in situ during the oxidation of pyrrole. The conductivity of composites exceeded the conductivities of the parent components. This synergistic effect is explained by the deposition of more conducting ordered polypyrrole at first, and less conducting globular polypyrrole later after the whole available tungsten disulfide surface was coated. Such scenario was confirmed by electron microscopies. Raman and X-ray photoelectron spectroscopies proved the completeness of the coating. Despite the increase in the conductivity, the electrocatalysis of hydrogen evolution reaction on tungsten disulfide was reduced after polypyrrole deposition, confirming effective coating of the substrate. A simple mixture of both components, however, improved the electrocatalytic effect compared with the composite or any of its components.
Materials Chemistry and Physics, 2018
properties of lignin/polypyrrole composites and their carbonized analogues, (2018),
Smart Materials and Structures, Sep 19, 2013
ABSTRACT The photo-actuation behavior of nanocomposites based on ethylene–vinylacetate copolymer ... more ABSTRACT The photo-actuation behavior of nanocomposites based on ethylene–vinylacetate copolymer (EVA) and styrene–isoprene–styrene (SIS) block copolymer filled with well-dispersed and modified multiwalled carbon nanotubes (MWCNTs) is discussed in this paper. The nanocomposites were prepared by casting from solution. To improve the dispersion of the MWCNTs in EVA, the MWCNT surface was modified with a non-covalent surfactant, cholesteryl 1-pyrenecarboxylate (PyChol). To prepare SIS nanocomposites, the MWCNT surface was covalently modified with polystyrene chains. The good dispersion of the filler was confirmed by transmission electron microscopy (TEM). Special, custom-made punch/die molds were used to create a Braille element (BE)-like shape, which under shear forces induces a uniaxial orientation of the MWCNTs within the matrix. The uniaxial orientation of MWCNTs is an essential precondition to ensure the photo-actuating behavior of MWCNTs in polymeric matrices. The orientation of the MWCNTs within the matrices was examined by scanning electron microscopy (SEM). Nanocomposite BEs were illuminated from the bottom by a red light-emitting diode (LED), and the photo-actuation was investigated by confocal laser scanning microscopy (CLSM). When the BEs were exposed to light, a temporary increase in the height of the element was detected. This process was observed to be reversible: after switching off the light, the BEs returned to their original shape and height.
Composites Part A-applied Science and Manufacturing, Mar 1, 2016
This study aims to investigate experimentally the effects of aspect ratio (length/diameter ratio)... more This study aims to investigate experimentally the effects of aspect ratio (length/diameter ratio) and concentration of multiwalled carbon nanotubes (MWCNTs) on thermal properties of high density polyethylene (HDPE) based composites. The aspect ratios of two types of MWCNT fillers are in the range of 200-400 and 500-3000. Composite samples were prepared by melt mixing up to weight fraction of 19% filler content, followed by a compression molding. Measurements of density, specific heat and thermal diffusivity (by modulated photothermal radiometry, PTR) were performed and effective thermal conductivities k e of nanocomposites were calculated using these values. The results show that the composites containing MWCNTs with higher aspect ratio have higher thermal conductivities than the ones with lower aspect ratio. In terms of conductivity enhancement k e /k m À 1, the results indicate that MWCNTs with higher aspect ratio provide three to fourfold larger enhancement than the ones with lower aspect ratio, at low filler concentrations.
Archives of materials science and engineering, 2008
Hybrid ethylene-propylene-diene-monomer (EPDM) nanocomposite foams were produced via compression ... more Hybrid ethylene-propylene-diene-monomer (EPDM) nanocomposite foams were produced via compression molding with enhanced electromagnetic wave absorption efficiency. The hybrid filler, consisting of 20 phr ferroelectric barium titanate (BT) and various loading fractions of multi-wall carbon nanotubes (MWCNTs), synergistically increased the electromagnetic (EM) wave absorption characteristics of the EPDM foam. Accordingly, while the EPDM foam filled with 20 phr BT was transparent to the EM wave within the frequency range of 8.2-12.4 GHz (X-band), the hybrid EPDM nanocomposite foam loaded with 20 phr BT and 10 phr MWCNTs presented a total shielding effectiveness (SE) of~22.3 dB compared to~16.0 dB of the MWCNTs (10 phr). This synergistic effect is suggested to be due to the segregation of MWCNT networks within the cellular structure of EPDM, resulting in enhanced electrical conductivity, and also high dielectric permittivity of the foam imparted by the BT particles. Moreover, the total SE of the BT/MWCNTs loaded foam samples remained almost unchanged when subjected to repeated bending due to the elastic recovery behavior of the crosslinked EPDM foamed nanocomposites.
Mikrochimica Acta, Dec 17, 2019
An electrochemical study was performed on the behavior of Ti 3 C 2 T x MXenes prepared by using e... more An electrochemical study was performed on the behavior of Ti 3 C 2 T x MXenes prepared by using either HF (MXene1) or LiF/HCl as etchants (MXene2). The use of two redox probes indicates the presence of a higher negative charge density on MXene2 in comparison to MXene1. The characterization of two nanomaterials shows that titanium and fluoride are present higher by one order of magnitude at the interface of MXene2, compared to MXene1. The high Ti and F content is accompanied by a 82-fold larger (249 μA•cm −2 vs. 5.64 μA•cm −2) anodic peak at the peak potential near 0.4 V (vs. Ag/AgCl). Similarly, the peak current on MXene2 is 317-fold higher for the oxygen reduction at pH 7.0 (at a voltage of −0.84 V) and 215-fold higher for the reduction of H 2 O 2 at −0.89 V, when compared to MXene1. Keywords MXene. Ti 3 C 2 T X. Electrocatalysis. Electrochemistry. H 2 O 2 reduction. Oxygenreduction reactions. Redox stability
Composites Part B-engineering, Oct 1, 2013
High-density polyethylene (HDPE) was reinforced with expanded and untreated graphite in a meltcom... more High-density polyethylene (HDPE) was reinforced with expanded and untreated graphite in a meltcompounding process. Viscosity increased upon addition of graphite phase, with the expanded graphite (EG) showing more dramatic rise than the untreated graphite (UG) in viscosity. The increase in viscosity was attributed to the increased surface-to-volume ratio for the EG filler after acid treatment. Electrical conductivity also increased from that pertaining to an insulator to one characteristic of a semiconductor. The EG system showed a lower percolation threshold for transition in conductivity compared to that in the UG system. DSC results indicated that the fillers acted as a nucleating agent in inducing the crystallization of HDPE in the composites. However, the overall degree of crystallinity and melting temperature of HDPE decreased with the addition of EG and UG. Mechanical properties improved as a function of filler content but the overall enhancement was not impressive. It was conjectured that the filler-matrix interface was not optimized in the melt-mixing process. However, the role of EG as a reinforcement phase for both electrical and mechanical properties was unambiguously established. The EG composites demonstrated potentially useful attributes for antistatic, barrier, mechanical, electrical, and cost-effective applications.
Procedia Engineering, 2015
In polymer composites and nanocomposites with conducting fillers, conductivity changes significan... more In polymer composites and nanocomposites with conducting fillers, conductivity changes significantly with strain and with the evolution of damage, which forms the basis for using the composite itself as sensor (self-sensing) for strain and for structural health monitoring. Less frequent is the use of capacitance sensors, where the changes of capacitance of the sample during deformation are utilized. Here we present results of recent work in the use of electrical dc measurements to monitor strain and to follow the onset and evolution of damage in selected examples of polymer composites and nanocomposites, pointing out differences in their properties. The materials we measured were PP (Poly-Propylene) filled with unfunctionalized MWCNTs (Multi Walled Carbon Nano-Tubes), SBR (Styrene Butadiene Rubber) filled with CB (Carbon Black) and PEEK (Poly-Ether-Ether-Ketone) reinforced with CFs (Carbon Fibers).
Polymer Engineering and Science, 2007
Novel silicon carbide/polypyrrole (SiC/PPy) conducting composites were prepared using silicon car... more Novel silicon carbide/polypyrrole (SiC/PPy) conducting composites were prepared using silicon carbide as inorganic substrate in the presence or absence of an anionic surfactant, dodecylbenzenesulfonic acid (DBSA). The surface modification of SiC particles was performed in aqueous solution containing the anionic surfactant by oxidative polymerization of pyrrole using ferric chloride as oxidant. Ash content analysis was used to determine the mass loading of organic fraction in the SiC/PPy composites. Scanning electron microscopy showed the surface modification of SiC by PPy. The presence of PPy in the composites was confirmed by infrared spectroscopy. The small gradual red shift of the band of the stretching vibrations of SiCO and SiOSi bonds and more intensive of PPy spectrum were observed when DBSA was used for composite preparation. The presence of both polypyrrole and surfactant was also detected by their respective N1s and S2p core level peaks recorded by X‐ray photoelectron spectroscopy. The electrical conductivity of SiC‐DBSA/PPy composites depends on PPy content at the surface and on pyrrole/DBSA molar ratio. The DBSA‐containing composites have a conductivity about 2 orders of magnitude higher than in the case of the composites prepared without DBSA when PPy loading was lower than 15 wt%. Above this PPy loading the difference in conductivity almost diminished due to a increased amount of PPy polymerized on the surface of the SiC substrate. SiC‐DBSA/PPy composites containing 15 wt% PPy prepared using a molar ratio pyrrole/DBSA = 5, exhibited a very hydrophobic behavior compared to the corresponding DBSA‐free composites, as they floated on water and did not sediment even after a prolonged period of time. POLYM. ENG. SCI., 47:1198–1206, 2007. © 2007 Society of Plastics Engineers
Journal of Nanophotonics, Oct 17, 2012
Abstract. The photo-actuating behavior of new polymeric nanocomposite materials based on a commer... more Abstract. The photo-actuating behavior of new polymeric nanocomposite materials based on a commercial elastomer, an ethylene-vinylacetate copolymer (EVA), filled with multiwalled carbon nanotubes (MWCNT) was investigated. A good dispersion of the MWCNT within the elastomeric matrix was ensured by using a novel, specific compatibilizer consisting of pyrenyl and cholesteryl groups. A uniaxial orientation of the MWCNT within the matrix was induced with shear forces by employing a special custom-made punch/die system. Good dispergation and alignment of the MWCNT within the matrix were demonstrated by scanning electron microscopy. Transmission electron microscopy showed a good dispersion of the MWCNT within the composite. Photo-actuation was qualitatively characterized by atomic force microscopy and quantitatively characterized by nanoindentation. The samples prepared in the form of Braille element showed expansion upon illumination by light diodes. The maximal height deformation changes about 15% was detected when a blue diode was used.
Materials Research Bulletin, May 1, 2005
Novel silicon carbide/polypyrrole (SiC/PPy) conducting composites were prepared using silicon car... more Novel silicon carbide/polypyrrole (SiC/PPy) conducting composites were prepared using silicon carbide as inorganic substrate. The surface modification of SiC was performed in aqueous solution by oxidative polymerization of pyrrole using ferric chloride as oxidant. Elemental analysis was used to determine the mass loading of polypyrrole in the SiC/PPy composites. Scanning electron microscopy showed the surface modification of SiC by PPy. PPy in composites was confirmed by the presence of PPy bands in the infrared spectra of SiC/PPy containing various amounts of conducting polymer. The conductivity of SiC/PPy composites depends on PPy content on the surface. The composite containing 35 wt.% PPy showed conductivity about 2 S cm À1 , which is in the same range as the conductivity of pure polypyrrole powder prepared under the same conditions using the same oxidant. PPy in the composites was clearly detected by X-ray photoelectron spectroscopy (XPS) measurements by its N1s and Cl2p peaks. High resolution scans of the C1s regions distinguished between silicon carbide and polypyrrole carbons. The fraction of polypyrrole at the composite surface was estimated from the silicon and nitrogen levels. The combination of XPS and conductivity measurements suggests that the surface of the SiC/PPy composites is polypyrrole-rich for a conducting polymer mass loading of at least 12.6 wt.%.
Polymer Degradation and Stability, 2003
The electrical properties of polymer composites-polyethylene/carbon black (PE/CB), polyethylene/c... more The electrical properties of polymer composites-polyethylene/carbon black (PE/CB), polyethylene/carbon black modified by polypyrrole (PE/CB-PPy), and polyethylene/carbon black modified by polyaniline (PE/CB-PANI)-were investigated during slow cyclic heating and cooling thermal ageing. Conductivity in composites was measured in heating/cooling cycles in the temperature range from 16 to 125 C. Scanning electron microscopy was used for morphology study of surface of modified CB particles. It was found that the thermal treatment resulted in a conductivity increase in all composites when heated below the melting point of PE. This effect was explained by increased crystallinity in the polymer matrix of thermally treated composites and confirmed by DSC analysis. The thermal ageing during the heating above the melting point of polymer matrix caused decrease in conductivity of PE/ CB composites, but increase of conductivity in composites containing CB-PPy or CB-PANI as a filler. The modified fillers create more perfect and thermally resistant conducting network in PE matrix. The temperature of decomposition maximum of PE/CB-PPy and PE/CB-PANI composites into higher compared with PE/CB composite as observed by thermogravimetric analysis.
Synthetic Metals, Apr 1, 2010
The conducting polymers, polypyrrole and polyaniline, were synthesized by chemical oxidative poly... more The conducting polymers, polypyrrole and polyaniline, were synthesized by chemical oxidative polymerization of the corresponding monomers in 0.1 M sulfuric acid using cerium(IV) sulfate as the oxidant at mole ratios of oxidant-to-monomer ranging from 0.5 to 3. The yields of the oxidation products were determined, and the samples were characterized with respect to their elemental composition, molecular structure, and morphology. The conductivity of polypyrrole prepared in 0.1 M sulfuric acid, 10 −1 to 10 0 S cm −1 , was higher compared with the conductivity of polyaniline prepared under the same conditions, 10 −3 to 10 −1 S cm −1. The loss of mass after deprotonation with ammonium hydroxide is reported, and discussed in terms of the type of protonation as also reflected by FTIR spectroscopy. The conductivity of polypyrrole bases remained at relatively high level, 10 −5 to 10 −3 S cm −1 , while PANI bases became non-conducting, 10 −12 to 10 −10 S cm −1. The polymers had a granular morphology in all cases.
Synthetic Metals, Jul 1, 2003
Conducting and stable polypyrrole (PPy) was synthesized by chemical oxidative polymerization of p... more Conducting and stable polypyrrole (PPy) was synthesized by chemical oxidative polymerization of pyrrole in aqueous solution containing an oxidant, ferric sulfate, and a surfactant. Anionic surfactants: sodium dodecylbenzenesulfonate, dodecylbenzenesulfonic acid, sodium dodecyl sulfate, poly(ethylene oxide)-n-alkyl-3-sulfopropyl ether potassium salt; cationic surfactant: tetradecyltrimethylammonium bromide; and non-ionic surfactants: poly(ethylene oxide) (10) iso-octylphenyl ether (Triton 1 X-100), poly(ethylene oxide) (20) sorbitan monolaurate (Tween 1 20) and poly(ethylene oxide) (20) sorbitan monostearate (Tween 1 60) were used as additives. Results of the elemental analysis and FTIR spectroscopy proved that only the anionic surfactants were incorporated into PPy similarly as the doping anion. This leads to a better stability towards the deprotonation. Also thermal stability, checked by TGA in air, was improved. Scanning electron microscopy studies showed that the presence of the anionic surfactant strongly influenced the morphology of the polymer product.
Nanotechnology, May 10, 2021
High-density polyethylene (HDPE)-based hybrid nanocomposites containing graphene nanoplatelets (G... more High-density polyethylene (HDPE)-based hybrid nanocomposites containing graphene nanoplatelets (GnPs) and multiwall carbon nanotubes (MWCNTs) were fabricated using melt mixing followed by compression molding. The influences of size and weight ratio of both carbon-based nanofillers on the electrical, thermal, and mechanical properties of hybrid nanocomposites were evaluated. This study proves that the size and weight ratio of carbon-based nanofillers play a critical role in determining these properties. The optimum size and weight ratio of GnPs and MWCNTs are determined at the maximum achieved enhancement for each property. The HDPE-based nanocomposites containing GnPs with larger surface area and MWCNTs with higher aspect ratio display the highest electrical conductivity at GnPs/MWCNTs weight ratio of 2/3. The combination of GnPs with larger surface area and MWCNTs with lower aspect ratio provides the maximum Young’s modulus enhancement of hybrid nanocomposites at 1/4 weight ratio of GnPs and MWCNTs. The nanocomposite containing GnPs with the largest lateral size and MWCNTs with a higher aspect ratio at a 3/2 weight ratio exhibits the highest thermal conductivity. Also, at around the percolation threshold of GnPs, the incorporation of MWCNTs with larger aspect ratio into the HDPE-based nanocomposites containing GnPs with the largest lateral size shows a distinct synergic effect on the thermal conductivity and Young’s modulus, while an additive effect on the electrical conductivity and thermal stability.
Proceedings of SPIE, Sep 8, 2011
Photomechanical actuation is preferred to electromechanical transduction because of some advantag... more Photomechanical actuation is preferred to electromechanical transduction because of some advantages including wireless connection, a producing low noise, fast response etc. However, only few materials actually exhibit photoactuation. Recently, nanotube-enriched elastomeric polymers have shown photo-actuating properties; the best results were reported for liquid crystals elastomers. In the present paper we discuss photo-actuating behavior of new photoactuating materials based on the
Materials, Sep 15, 2018
The electrospinning of an ethylene vinyl acetate (EVA) copolymer with a vinyl acetate content of ... more The electrospinning of an ethylene vinyl acetate (EVA) copolymer with a vinyl acetate content of 28 wt.% is limited due to the solubility of the copolymer in standard laboratory conditions. Poly(lactic acid) (PLA) is a biodegradable polymer that can be electrospun easily. However, PLA has limited applicability because it is brittle. Blends of these polymers are of interest in order to obtain new types of materials with counterbalanced properties originating from both polymeric compounds. The fibers were electrospun on a water surface from a solution mixture containing various weight ratios of both polymers using a dichloromethane and acetone (70:30 v/v) mixture as solvent. The morphologies of the prepared non-woven mats were examined by scanning electron microscopy (SEM), and the chemical composition was investigated by X-ray photoelectron spectroscopy (XPS) and by Fourier Transform Infrared Spectroscopy (FTIR). The fibers' thermal properties and stability were examined, and the mechanical properties were tested. The results showed that the strength and flexibility of the blend samples were enhanced by the presence of PLA.
International Journal of Thermal Sciences, Dec 1, 2012
This work aimed at thermal transport characterization of high density polyethylene (HDPE) filled ... more This work aimed at thermal transport characterization of high density polyethylene (HDPE) filled with 5 and 50 mm expanded graphite (EG) particles and with 0.4 mm unexpanded graphite (UG) particles. Sample platelets were produced by melt mixing followed by compression molding. Thermal conductivity k was determined by combining measurements of density, specific heat capacity and thermal diffusivity, the latter by modulated photothermal radiometry (PTR). Starting from an effective medium approximation model, we derived a linearized expression for the effective k of composites with low particle charge. It explains the unusually high experimental k values (up to four-fold increase) as the effect of strongly non-spherical EG particles (aspect ratio 1/p ¼ 110e290). Larger particle sizes produce higher k enhancement, while the interfacial thermal resistance (R bd ¼ 2.1,10 À7 m 2 ,K/W) has an opposite effect. The same model is consistent with experimental k for low particle charge HDPE/UG composites. At higher particle charge the model fails due to particle interaction leading to validity break of the effective medium approximation.
Materials Research Express, 2019
The effects of the aspect ratio and the addition of multiwall carbon nanotubes (MWCNTs) on the mo... more The effects of the aspect ratio and the addition of multiwall carbon nanotubes (MWCNTs) on the morphological, electrical, mechanical and thermal properties of high-density polyethylene (HDPE)-based nanocomposites are investigated. The HDPE nanocomposites with various amounts up to 18.74 wt.% of MWCNTs that have two different aspect ratios (AR), (200–400(M58) and 500–3000(M12)) were prepared by a melt mixing method, followed by compression molding. The results demonstrate that the addition of MWCNTs enhances the electrical, mechanical and thermal properties of the HDPE/MWCNTs nanocomposites. The HDPE nanocomposites with higher aspect ratio MWCNTs demonstrated a slightly better enhancement in the morphological and electrical properties than the other ones with lower aspect ratio MWCNTs. Additionally, Young's modulus and the thermal stability increased with increasing aspect ratio of MWCNTs.
Applied Surface Science, 2019
A conducting polymer, polypyrrole, was deposited on tungsten disulfide flakes in situ during the ... more A conducting polymer, polypyrrole, was deposited on tungsten disulfide flakes in situ during the oxidation of pyrrole. The conductivity of composites exceeded the conductivities of the parent components. This synergistic effect is explained by the deposition of more conducting ordered polypyrrole at first, and less conducting globular polypyrrole later after the whole available tungsten disulfide surface was coated. Such scenario was confirmed by electron microscopies. Raman and X-ray photoelectron spectroscopies proved the completeness of the coating. Despite the increase in the conductivity, the electrocatalysis of hydrogen evolution reaction on tungsten disulfide was reduced after polypyrrole deposition, confirming effective coating of the substrate. A simple mixture of both components, however, improved the electrocatalytic effect compared with the composite or any of its components.
Materials Chemistry and Physics, 2018
properties of lignin/polypyrrole composites and their carbonized analogues, (2018),