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Item type:Publication, Access status: without files , Tailored crystalline width and wall thickness of an annealed 3D carbon foam composites and its mechanical propertyCarbon nanostructures in form of 3D carbon foams are mainly popular in materials community because of their ultralow densities, variable morphologies, and remarkable properties, etc. One of these foams is Aerographite, which exhibits a tetrapodal interconnected morphology. Similar to other synthetic carbon structures, the lattice defects are formed during the synthesis of Aerographite, which can be healed by a post-thermal treatment. Aerographite shows a property dependency on wall thickness (number of graphitic layers), which affects both, the electrical and mechanical properties. In this study, the wall thickness is tailored by varying of the total reaction time during the replication process. The influence of the thermal treatment of Aerographite on its mechanical performance in an Aerographite-epoxy nanocomposite, by determining the fracture toughness (K 1C ) in three-point bending tests (SEN-3PB), is investigated. An increase of the fracture toughness with increasing wall thickness is observed for untreated Aerographite. The graphitization of Aerographite leads to a reduction of the mechanical properties, by increasing the crystalline width. Consequently, the measured fracture toughness is dependent on the graphitization, the calculated crystalline width and the wall thickness of tubes in the hollow Aerographite tetrapodal network. Finally, based on these relations, a phenomenological mechanical failure model is developed and briefly discussed.Publicationtype: Journal Article204 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , 3D carbon networks and their polymer composites: fabrication and electromechanical investigations of neat aerographite and aerographite-based PNCs under compressive load(Elsevier, 2017-09-20); ; ; ; Aerographite is a lightweight 3D nanocarbon network which offers covalent interconnections for polymer nanocomposites (PNCs). Here, the electrical and mechanical properties of neat Aerographite and Aerographite-based PNCs are investigated in detail. The Aerographite filler networks consist of hollow, graphitic tubes of μm-sized diameters and nm-sized wall thicknesses. Different densities of Aerographite in the range of 0.6–13.9 mg/cm3 have been investigated towards their mechanical deformation behavior, electrical conductivities and piezoresistive response under compression. This basic characterization of filler networks is compared to resulting PNCs if the Aerographite is fully embedded in epoxy matrix. It can be shown that the use of 3D interconnected Aerographite results in high electrical conductivities at low filler contents, e.g., 2–8.7 S/m for weight fractions of 0.1–1.2 wt.-%. The neat Aerographite has been characterized in detail by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy techniques. To explain the observed piezoresistive behavior of these 3D nanocarbon-based PNCs, a qualitative micromechanical model is introduced. The model describes the internal graphitic wall slippage and loss of interconnections of the inner electrically conductive networks under load. The piezoresistive response of Aerographite-based PNCs can be directly correlated to the applied outer mechanical loads.Publicationtype: Journal Article173 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Erratum: On the manufacturing and electrical and mechanical properties of ultra-high wt.% fraction aligned MWCNT and randomly oriented CNT epoxy composites (Carbon (2015) 91 (275-290))(Elsevier, 2015-11-14); ; ; ; Publicationtype: Journal Article60 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , On the manufacturing and electrical and mechanical properties of ultra-high wt.% fraction aligned MWCNT and randomly oriented CNT epoxy composites(Elsevier, 2015-05-02); ; ; ; The effect of CNT orientation on electrical and mechanical properties is presented on the example of an ultra-high filler loaded multi-walled carbon nanotube (68 wt.% MWCNTs) epoxy-based nanocomposite. A novel manufacturing method based on hot-press infiltration through a semi-permeable membrane allows to obtain both, nanocomposites with aligned and randomly oriented CNTs (APNCs and RPNCs) over a broad filler loading range of ≈10-68 wt.%. APNCs are based on low-defected, mm-long aligned MWCNT arrays grown in chemical vapour deposition (CVD) process. Electrical conductivity and mechanical properties were measured parallel and perpendicular to the direction of CNTs. RPNCs are based on both, aligned mm-long MWCNTs and randomly oriented commercial μm-long and entangled MWCNTs (Baytube C150P, and exemplarily Arkema Graphistrength C100). The piezoresistive strain sensing capability of these high-wt.% APNCs and RPNCs had been investigated towards the influence of CNT orientations. For the highest CNT fraction of 68 wt.% of unidirectional aligned CNTs a Young's modulus of E|| ≈ 36 GPa and maximum electrical conductivity of σ|| ≈ 37·10⁴ S/m were achieved.Publicationtype: Journal Article76 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The production of aligned MWCNT/polypyrrole composite films(Elsevier, 2013-04-15); ; ; ; We synthesized highly porous composite films of vertically aligned carbon nanotubes (CNTs) and polypyrrole (PPy) by employing a simple in situ electropolymerisation process from aqueous pyrrole solutions. By contacting the entire CNT array, each CNT acts as a highly active anode that facilitates uniform deposition and immediate polymerization of pyrrole directly on the CNT surface. As a result, each individual CNT was coated with a thin layer of PPy with a tunable thickness between 4 and 38 nm. At the same time the vertical array structure of the CNTs was preserved. A major advantage of this route is that the resulting composite film is highly porous and can be post-filled with other polymers, metals or ceramics to create new multifunctional composites and hybrid structures.Publicationtype: Journal Article62 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The imaging mechanism, imaging depth, and parameters influencing the visibility of carbon nanotubes in a polymer matrix using an SEMVisualization of embedded carbon nanotubes (CNTs) in polymer using a scanning electron microscope (SEM) has been established as a convenient technique to evaluate CNT dispersion. This technique is known as voltage contrast imaging and is different from material contrast and topographic contrast imaging. By investigating CNT/epoxy composites the voltage contrast imaging theory is further understood. Trapping of electrons at the CNT/epoxy interface induces a local potential difference which enhances the image contrast. By coating the composite with a polymer film of different thicknesses the imaging depth (i.e. from how deep the CNTs can be seen) is determined to be up to 250 nm, and is a function of the accelerating voltage of the SEM. Visibility of CNTs is found to be sensitive to the CNT dispersion and concentration, as well as to the accelerating voltage.Publicationtype: Journal Article16 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Imaging of CNTs in a polymer matrix at low accelerating voltages using a SEMAs continued work of scanning electron microscope visualization of carbon nanotubes (CNTs) in epoxy matrix at high accelerating voltage (from 3 to 15 kV), this study focuses on the low accelerating voltage range (from 0.3 to 5.0 kV). In the CNT/epoxy composite, the CNT contrast is observed to invert two times as the accelerating voltage increases from 0.3 to 5.0 kV. At 0.7 kV the CNT contrast shifts from bright to dark, and after 1.5 kV bright CNTs are observed again. The contrast inversion and imaging mechanism of CNTs are interpreted in correlation with the secondary electron (SE) yield curve of epoxy. At 0.3-0.6 kV the epoxy is positively charged, which results in influx of electrons (from the ground) through the CNTs. These electrons lower the potential of the CNTs and enhance the local SE emission. The bright CNTs contrast at >1.5 kV is attributed to the high SE yield resulting from the trapping of injected primary electrons (PEs) in the CNTs. At 0.7 and 1.0 kV the dark CNT contrast may be attributed to the weak PEs-CNTs interaction or to the slight charging of epoxy. Further observation suggests that latter is more likely to occur.Publicationtype: Journal Article18