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Alan H. Windle - One of the best experts on this subject based on the ideXlab platform.
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Thermal and Electrical conductivity of single- and multi-walled carbon nanotube-epoxy composites
Composites Science and Technology, 2006Co-Authors: Anna Moisala, Qiuwu Li, Ian A. Kinloch, Alan H. WindleAbstract:The Electrical and thermal conductivities of epoxy composites containing 0.005-0.5 wt% of single-walled (SWNTs) or multi-walled (MWNTs) carbon nanotubes have been studied. The MWNT composites had an Electrical Percolation Threshold of
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ultra low Electrical Percolation Threshold in carbon nanotube epoxy composites
Polymer, 2003Co-Authors: Jan Kurt Walter Sandler, Ian A. Kinloch, J E Kirk, Milo S P Shaffer, Alan H. WindleAbstract:Abstract Epoxy composites based on aligned CVD-grown multi-wall carbon nanotubes with weight fractions ranging from as low as 0.001 up to 1 wt% were produced. The resulting Electrical properties were analysed by AC impedance spectroscopy. The composite conductivity σ follows a Percolation scaling law of the form σ ∝( p − p c ) t with the critical mean concentration p c to form a conductive network of approximately 0.0025 wt% and an exponent, t , of 1.2. The results are compared to previous studies investigating the Percolation behaviour of entangled carbon nanotubes and spherical carbon black particles in the same matrix processed under similar conditions. The experimental Percolation Threshold for the aligned nanotubes used in this study represents the lowest Threshold observed for carbon-nanotube-based polymer composites yet reported.
Petra Potschke - One of the best experts on this subject based on the ideXlab platform.
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a promising approach to low Electrical Percolation Threshold in pmma nanocomposites by using mwcnt peo predispersions
Materials & Design, 2016Co-Authors: Seyed Mohammad Mir, Nader Taheri Qazvini, Petra Potschke, Beate Krause, Seyed Hassan Jafari, Hossein Ali KhonakdarAbstract:Abstract Electrical conductive poly(methyl methacrylate) (PMMA) nanocomposites with low Percolation Threshold are very challenging to be prepared. Here, we show that the miscibility between poly(ethylene oxide) (PEO) as matrix for predispersions of multi-walled carbon nanotubes (MWCNTs) and PMMA represents an efficient approach to achieve very low Electrical Percolation Threshold. PMMA/PEO-MWCNTs nanocomposites were prepared by a two-step solution casting method involving pre-mixing of MWCNTs with PEO and then mixing of PEO-MWCNTs with PMMA, resulting in a PMMA/PEO ratio of 80/20 wt%. The Electrical Percolation Threshold (EPT) value was determined to be ~ 0.07 wt% which is significantly lower than most of the reported EPT values in the literature for PMMA/CNT composites. The very low Electrical Percolation Threshold was attributed to the effectual role of PEO in self-assembly of secondary structures of nanotubes into an Electrically conductive network. This was further confirmed by transmission electron microscopy and by comparing the obtained EPT value with the prediction of the excluded volume model in which statistical Percolation Threshold is defined based on uniform distribution of high-aspect ratio sticks in a matrix. Moreover, based on UV–Vis measurements and linear viscoelastic rheological measurements, optical and rheological Percolation Thresholds were obtained at nearly 0.01 wt% and 0.5 wt%, respectively.
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ultralow Percolation Threshold in polyamide 6 6 mwcnt composites
Composites Science and Technology, 2015Co-Authors: Beate Krause, Liane Hausler, Regine Boldt, Petra PotschkeAbstract:When incorporating multiwalled carbon nanotubes (MWCNTs) synthesised by the aerosol-CVD method using different solvents into polyamide 6.6 (PA66) by melt mixing an ultralow Electrical Percolation Threshold of 0.04 wt.% was found. This very low Threshold was assigned to the specific characteristic of the MWCNTs for which a very high aspect ratio, a good dispersability in aqueous surfactant dispersions, and relatively low oxygen content near the surface were measured. The investigation of the composites by transmission electron microscopy on ultrathin cuts as well as by scanning electron microscopy combined with charge contrast imaging on compression moulded plates illustrated a good MWCNT dispersion within the PA66 matrix and that the very high aspect ratio of the nanotubes remained even after melt processing. Additionally, the thermal behaviour of the PA66 composites was investigated using differential scanning calorimetry (DSC) showing that the addition of only 0.05 wt.% MWCNT leads to an increase of the onset crystallization temperature of 11 K.
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Electrical and thermal properties of polyamide 12 composites with hybrid fillers systems of multiwalled carbon nanotubes and carbon black
Composites Science and Technology, 2011Co-Authors: Robert Socher, Beate Krause, Sylvia Hermasch, Roland Wursche, Petra PotschkeAbstract:Hybrid filler systems of multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) were incorporated into two types of polyamide 12 (PA12) using small-scale melt mixing in order to identify potential synergistic effects on the interaction of these two Electrical conductive fillers. Although no synergistic effects were observed regarding the Electrical Percolation Threshold, at loadings well above the Percolation Threshold higher volume conductivities were obtained for samples containing both, MWCNT and CB, as compared to single fillers. This effect was more pronounced when using a higher viscous PA12 matrix. The formation of a co-supporting network can be assumed. The combined use of CB and MWCNTs improved the macrodispersion of MWCNT agglomerates, which can be assigned as a synergistic effect. DSC measurements indicated an effect of the nanofiller on crystallisation temperatures of PA12; however this was independent of the kind or amount of the carbon nanofiller.
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highly conducting poly methyl methacrylate carbon nanotubes composites investigation on their thermal dynamic mechanical Electrical and dielectric properties
Composites Science and Technology, 2011Co-Authors: Emmanuel Logakis, Polycarpos Pissis, C Pandis, J Pionteck, Petra PotschkeAbstract:Abstract Nanocomposites of poly(methyl methacrylate) (PMMA) containing various multi-walled carbon nanotubes (MWCNT) contents were prepared using melt mixing. Several techniques were employed to study the influence of the MWCNT addition on the thermal, mechanical, Electrical and dielectric properties of the PMMA matrix. The Electrical Percolation Threshold ( p c ) was found to be 0.5 vol.% by performing AC and DC conductivity measurements. Significantly high conductivity levels ( σ dc ) were achieved: σ dc exceeds 10 −2 S/cm already at 1.1 vol.%, the criterion for EMI shielding ( σ dc > 10 −1 S/cm) is fulfilled at 2.9 vol.%, and the highest loaded sample (5.2 vol.%) gave a maximum value of 0.5 S/cm. Dielectric relaxation spectroscopy measurements in broad frequency (10 −1 −10 6 Hz) and temperature ranges (−150 to 170 °C) indicated weak polymer–filler interactions, in consistency with differential scanning calorimetry and dynamic-mechanical analysis findings. Weak polymer–filler interactions and absence of crystallinity facilitate the achievement of high conductivity levels in the nanocomposites.
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low Electrical Percolation Threshold in poly ethylene terephthalate multi walled carbon nanotube nanocomposites
European Polymer Journal, 2010Co-Authors: Emmanuel Logakis, Polycarpos Pissis, Doris Pospiech, Andreas Korwitz, Beate Krause, Uta Reuter, Petra PotschkeAbstract:Abstract Poly(ethylene terephthalate) (PET)/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by three different methods: in-situ polymerization technique (I-S), direct mixing in the melt (DM) and dilution of a 0.5 wt.% masterbatch, synthesized via in-situ polymerization, using melt mixing (MB). The morphology of the resulting nanocomposites was examined using scanning and transmission electron microscopy and their Electrical properties were characterized by ac conductivity measurements. The I-S series of samples exhibited an extremely low Electrical Percolation Threshold (pc ≈ 0.06 wt.%), as compared to values of similar systems previously mentioned in literature. The MB series showed a comparable pc value (pc: 0.05–0.10 wt.%), whereas the investigation revealed a higher pc in the DM series (pc: 0.10–0.20 wt.%). Finally, selected concentrations of samples were prepared using OH-functionalized MWCNT, following the I-S procedure. The conductivity of these samples was found to be lower than that of samples with non-functionalized MWCNT.
Raquel Verdejo - One of the best experts on this subject based on the ideXlab platform.
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highly deformable porous electromagnetic wave absorber based on ethylene propylene diene monomer multiwall carbon nanotube nanocomposites
Polymers, 2020Co-Authors: Hasti Izhani, Ali Asgha Katbab, Emil Lopezhernandez, J M Miranda, Raquel VerdejoAbstract:The need for electromagnetic interference (EMI) shields has risen over the years as the result of our digitally and highly connected lifestyle. This work reports on the development of one such shield based on vulcanized rubber foams. Nanocomposites of ethylene–propylene–diene monomer (EPDM) rubber and multiwall carbon nanotubes (MWCNTs) were prepared via hot compression molding using a chemical blowing agent as foaming agent. MWCNTs accelerated the cure and led to high shear-thinning behavior, indicative of the formation of a 3D interconnected physical network. Foamed nanocomposites exhibited lower Electrical Percolation Threshold than their solid counterparts. Above Percolation, foamed nanocomposites displayed EMI absorption values of 28–45 dB in the frequency range of the X-band. The total EMI shielding efficiency of the foams was insignificantly affected by repeated bending with high recovery behavior. Our results highlight the potential of cross-linked EPDM/MWCNT foams as a lightweight EM wave absorber with high flexibility and deformability.
Nader Taheri Qazvini - One of the best experts on this subject based on the ideXlab platform.
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a promising approach to low Electrical Percolation Threshold in pmma nanocomposites by using mwcnt peo predispersions
Materials & Design, 2016Co-Authors: Seyed Mohammad Mir, Nader Taheri Qazvini, Petra Potschke, Beate Krause, Seyed Hassan Jafari, Hossein Ali KhonakdarAbstract:Abstract Electrical conductive poly(methyl methacrylate) (PMMA) nanocomposites with low Percolation Threshold are very challenging to be prepared. Here, we show that the miscibility between poly(ethylene oxide) (PEO) as matrix for predispersions of multi-walled carbon nanotubes (MWCNTs) and PMMA represents an efficient approach to achieve very low Electrical Percolation Threshold. PMMA/PEO-MWCNTs nanocomposites were prepared by a two-step solution casting method involving pre-mixing of MWCNTs with PEO and then mixing of PEO-MWCNTs with PMMA, resulting in a PMMA/PEO ratio of 80/20 wt%. The Electrical Percolation Threshold (EPT) value was determined to be ~ 0.07 wt% which is significantly lower than most of the reported EPT values in the literature for PMMA/CNT composites. The very low Electrical Percolation Threshold was attributed to the effectual role of PEO in self-assembly of secondary structures of nanotubes into an Electrically conductive network. This was further confirmed by transmission electron microscopy and by comparing the obtained EPT value with the prediction of the excluded volume model in which statistical Percolation Threshold is defined based on uniform distribution of high-aspect ratio sticks in a matrix. Moreover, based on UV–Vis measurements and linear viscoelastic rheological measurements, optical and rheological Percolation Thresholds were obtained at nearly 0.01 wt% and 0.5 wt%, respectively.
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Gelatin-Graphene Nanocomposites with Ultralow Electrical Percolation Threshold
Advanced Materials, 2016Co-Authors: Hoda Nassira, Nader Taheri Qazvini, Stephan Handschin, Antoni Sánchez-ferrer, Jozef Adamcik, Hossein Mahdavi, Raffaele MezzengaAbstract:Gelatin-graphene conductive biopolymer nanocomposites (CPCs) with ultralow Percolation Threshold are designed by reducing in situ graphene oxide nanosheets with ascorbic acid and suppressing the aggregation of the graphene nanosheets. The resulting conductive nanocomposites show a record-low Electrical Percolation Threshold of 3.3 × 10(-2) vol%, which arises from the homogeneous dispersion of the graphene nanosheets within the gelatin matrix.
Karl Schulte - One of the best experts on this subject based on the ideXlab platform.
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Comparison of rheological and Electrical Percolation phenomena in carbon black and carbon nanotube filled epoxy polymers
Journal of Materials Science, 2011Co-Authors: Jan Sumfleth, Samuel T. Buschhorn, Karl SchulteAbstract:Epoxy nanocomposite suspensions including multi-wall carbon nanotubes (MWCNTs) and carbon black (CB) were produced and investigated by means of combined rheological and Electrical analysis. The rheological Percolation behaviour was compared to the Electrical Percolation behaviour. Due to similar dynamic agglomeration mechanisms the difference between the rheological and the Electrical Percolation Threshold in the cured state is identical for MWCNT and CB filled systems. Non-covalent matrix–nanoparticle interactions in uncured epoxy suspensions are negligible since the onset of Electrical and rheological Percolation in the uncured state coincidence. Furthermore, the Electrical Percolation Threshold in the cured state is always lower than in the uncured state because of the high tendency of CB and MWCNTs to form conductive networks during curing. The difference between rheological and Electrical Percolation Threshold is dependent on the curing conditions. Thus, the rheological Percolation Threshold can be considered as an upper limit for the Electrical Percolation Threshold in the cured state. Due to the formation of co-supporting networks multi-filler (MWCNTs and CB) suspensions exhibit a similar rheological behaviour as the binary MWCNT suspensions. For both types of suspensions a rheological Percolation Threshold of around 0.2 and 0.25 wt% was determined. Conversely, the binary CB nanocomposites exhibit a four-times higher Percolation Threshold of about 0.8 wt%. The difference between the binary MWCNT suspension and the ternary CB/MWCNT suspension in storage shear modulus at high filler concentrations (~0.8 wt%) turns out to be less than expected. Thus, synergistic effects in network formation are already present in the epoxy suspension and get more pronounced during curing.
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synergistic effects in network formation and Electrical properties of hybrid epoxy nanocomposites containing multi wall carbon nanotubes and carbon black
Journal of Materials Science, 2009Co-Authors: Jan Sumfleth, Xavier Cordobes Adroher, Karl SchulteAbstract:Epoxy nanocomposites including multi-wall carbon nanotubes (MWCNT) and carbon black (CB) were produced and investigated by means of Electrical conductivity measurements and microscopical analysis. Varying the weight fraction of the nanoparticles, Electrical Percolation behaviour was studied. Due to synergistic effects in network formation and in charge transport the inclusion of both MWCNT and CB in the epoxy matrix leads to an identical Electrical behaviour of this ternary nanocomposite system compared to the binary MWCNT-epoxy system. For both types of nanocomposites an Electrical Percolation Threshold of around 0.025 wt% and 0.03 wt% was observed. Conversely, the binary CB nanocomposites exhibit a three-times higher Percolation Threshold of about 0.085 wt%. The difference between the binary MWCNT-epoxy and the ternary CB/MWCNT-epoxy in Electrical conductivity at high filler concentrations (e.g. 0.5 wt%) turns out to be less than expected. Thus, a considerable amount of MWCNTs can be replaced by CB without changing the Electrical properties.