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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 , Individual hollow and mesoporous aero-graphitic microtube based devices for gas sensing applications(American Institute of Physics (AIP), 2017-06-27); ; ; ; In this work, individual hollow and mesoporous graphitic microtubes were integrated into electronic devices using a FIB/SEM system and were investigated as gas and vapor sensors by applying different bias voltages (in the range of 10 mV-1 V). By increasing the bias voltage, a slight current enhancement is observed, which is mainly attributed to the self-heating effect. A different behavior of ammonia NH3 vapor sensing by increasing the applied bias voltage for hollow and mesoporous microtubes with diameters down to 300 nm is reported. In the case of the hollow microtube, an increase in the response was observed, while a reverse effect has been noticed for the mesoporous microtube. It might be explained on the basis of the higher specific surface area (SSA) of the mesoporous microtube compared to the hollow one. Thus, at room temperature when the surface chemical reaction rate (k) prevails on the gas diffusion rate (DK) the structures with a larger SSA possess a higher response. By increasing the bias voltage, i.e., the overall temperature of the structure, DK becomes a limiting step in the gas response. Therefore, at higher bias voltages the larger pores will facilitate an enhanced gas diffusion, i.e., a higher gas response. The present study demonstrates the importance of the material porosity towards gas sensing applications.Publicationtype: Journal Article91 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Ultra-hoch gefüllte und orientierte CNT- und 3D-vernetzte Aerographit Epoxidkomposite: Synthese, Herstellung und EigenschaftenIn this work two different polymer nanocomposites (PNCs) with graphitic fillers in epoxy matrix are characterized. Both PNCs possess structural features, which are used to address open scientific questions in the field of carbon nanotube (CNT) based PNCs. The PNCs of this work use in-house synthesized nanoparticles, which are: mm-long, unidirectional aligned carbon nanotubes (CNTs) and covalently 3D interconnected graphite-based networks ('Aerographite', AG). For CNT-based PNCs (CNT-PNCs) a manufacturing method is introduced (patented), which allows to embed very high amounts of CNTs in epoxy matrix (Φ= 10-70 wt.%). Two different structures are given for these CNT-based PNCs: APNCs: PNCs with unidirectional alignment of mm-long, in-house produced CNTs (anisotropic). RPNCs: PNCs with randomly oriented CNTs (mm-long in-house produced CNTs or µm-long commercial CNT) (isotropic). AG-PNCs: Aerographite-based PNCs are PNCs with an isotropic, covalently interconnected graphite filler network embedded in epoxy matrix (Φ<1 wt.%) (isotropic). Here different orientations, different aspect ratios and different qualities of CNTs are directly compared. The scaling of electrical conductivity and Young's moduli in respect to filler loadings are in focus of the investigations (σ (Φ) , E(Φ)). The piezoresistive and thermoelectric behavior of CNT-based PNCs with filler loadings Φ >5 wt.% are investigated here for the first time. The findings for CNT-PNCs are combined with the results on AG-PNCs. The influence of inner network topologies on electrical conduction is discussed in detail. If the graphitic networks of AGs are infiltrated with epoxy, AG-PNCs of low filler loading and isotropic structure result. Inner graphite elements of AGs are covalently interconnected. Therefore AG-PNCs can be used to investigate the influence of reduced electron tunneling on the electrical conduction and piezoresistive behavior of PNCs. It can be shown, that highly filled APNCs can lead to highly improved material properties like electrical conductivities up to σ= 37000 S/m and Youngs's moduli up to E= 36 GPa. On the other hand APNCs are shown to follow similar scaling rules of electrical conduction (σ(Φ)), as they had been derived from dispersed CNT-PNCs in the last two decades of research. The inner interconnections of AG lead to - compared to all of today's CNT-based PNCs - effective electrical conduction (σ/Φ). Appendix: Aerographite (AG): In the year 2010 first time a metal oxide (ZnO) was shown to be a feasible substrate for graphite deposition via a chemical vapor deposition process (CVD). Technically no other synthesis offers following combination: (i) structuring by tailored ceramic networks & graphite deposition with in situ removal of template. The density and inner structure of AG can be altered by the CVD-process. Scientifically the details of nucleation and growth of graphite within the CVD-process is not yet fully understood. To continue the research, the appendix deal with following contents: Development of synthesis & outlook on structuring Statistics of CVD-processes (2010-2015) & introduction of one control parameter for selecting variant and density of AGs Structural analyses (SEM, TEM, SAEDs, XRD,…) & introduction of a hypothetical growth modelPublicationtype: Doctoral Thesis749 387 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Nanomechanics of individual aerographite tetrapods(Nature Publishing Group, 2017-04-12); ; ; ; Carbon-based three-dimensional aerographite networks, built from interconnected hollow tubular tetrapods of multilayer graphene, are ultra-lightweight materials recently discovered and ideal for advanced multifunctional applications. In order to predict the bulk mechanical behaviour of networks it is very important to understand the mechanics of their individual building blocks. Here we characterize the mechanical response of single aerographite tetrapods via in situ scanning electron and atomic force microscopy measurements. To understand the acquired results, which show that the overall behaviour of the tetrapod is governed by the buckling of the central joint, a mechanical nonlinear model was developed, introducing the concept of the buckling hinge. Finite element method simulations elucidate the governing buckling phenomena. The results are then generalized for tetrapods of different size-scales and shapes. These basic findings will permit better understanding of the mechanical response of the related networks and the design of similar aerogels based on graphene and other two-dimensional materials.Publicationtype: Journal ArticleScopus© Citations 30 425 515 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Hierarchical aerographite nano-microtubular tetrapodal networks based electrodes as lightweight supercapacitor(Elsevier, 2017-03-08); ; ; ; A great deal of interest has been paid to the application of carbon-based nano- and microstructured materials as electrodes due to their relatively low-cost production, abundance, large surface area, high chemical stability, wide operating temperature range, and ease of processing including many more excellent features. The nanostructured carbon materials usually offer various micro-textures due to their varying degrees of graphitisation, a rich variety in terms of dimensionality as well as morphologies, extremely large surface accessibility and high electrical conductivity, etc. The possibilities of activating them by chemical and physical methods allow these materials to be produced with further higher surface area and controlled distribution of pores from nanoscale upto macroscopic dimensions, which actually play the most crucial role towards construction of the efficient electrode/electrolyte interfaces for capacitive processes in energy storage applications. Development of new carbon materials with extremely high surface areas could exhibit significant potential in this context and motivated by this in present work, we report for the first time the utilization of ultralight and extremely porous nano-microtubular Aerographite tetrapodal network as a functional interface to probe the electrochemical properties for capacitive energy storage. A simple and robust electrode fabrication strategy based on surface functionalized Aerographite with optimum porosity leads to significantly high specific capacitance (640 F/g) with high energy (14.2 Wh/kg) and power densities (9.67×103 W/kg) which has been discussed in detail.Publicationtype: Journal Article94 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Low powered, tunable and ultra-light aerographite sensor for climate relevant gas monitoring(Royal Society of Chemistry (RSC), 2016-09-27); ; ; ; Increasing atmospheric CO2 gas pollution and emergence of new types of green energy sources require continuous environmental monitoring. In this context, fast, efficient, light, robust, and reliable gas sensors that can work at room temperature are in high demand. We report on a low-powered type of ultra-light sensor, based on a 3-D-microtube network from a 2-D graphene/nanographite, called aerographite, and a method to tune the nanosensor’s selectivity by a simple variation of the applied bias voltage. Adequate selectivity to CO2 and ultra-fast sensing of H2 by applying 1 V and 5 V, respectively, is obtained. At ultra-low applied bias voltages (1–100 mV) only very low power consumption (z3.6 nW for 1 mV) is needed. This is most important, as it can be run by energy harvesting methods. The presented results are of the highest interest in terms of low-cost production of ultra-light and ultra-low-power consumption gas sensors for environmental monitoring of greenhouse gases and their simplicity from the technological/engineering points of view.Publicationtype: Journal ArticleScopus© Citations 49 388 420 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Strong light scattering and broadband (UV to IR) photoabsorption in stretchable 3D hybrid architectures based on Aerographite decorated by ZnO nanocrystallites(Nature Publishing Group, 2016-09-12); ; ; ; In present work, the nano- and microscale tetrapods from zinc oxide were integrated on the surface of Aerographite material (as backbone) in carbon-metal oxide hybrid hierarchical network via a simple and single step magnetron sputtering process. The fabricated hybrid networks are characterized for morphology, microstructural and optical properties. The cathodoluminescence investigations revealed interesting luminescence features related to carbon impurities and inherent host defects in zinc oxide. Because of the wide bandgap of zinc oxide and its intrinsic defects, the hybrid network absorbs light in the UV and visible regions, however, this broadband photoabsorption behavior extends to the infrared (IR) region due to the dependence of the optical properties of ZnO architectures upon size and shape of constituent nanostructures and their doping by carbon impurities. Such a phenomenon of broadband photoabsorption ranging from UV to IR for zinc oxide based hybrid materials is novel. Additionally, the fabricated network exhibits strong visible light scattering behavior. The developed Aerographite/nanocrystalline ZnO hybrid network materials, equipped with broadband photoabsorption and strong light scattering, are very promising candidates for optoelectronic technologies.Publicationtype: Journal ArticleScopus© Citations 54 256 405 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Electro-mechanical piezoresistive properties of three dimensionally interconnected carbon aerogel (Aerographite)-epoxy composites(Elsevier, 2016-08-28); ; ; ; Aerographite (AG) is a carbon aerogel consisting of three-dimensionally (3D) interconnected graphitic microtubes. This study characterizes the electrical and mechanical properties of Aerographite/epoxy composites under tensile load. Aerographite can be used as a highly tailorable filler in polymer nanocomposites (PNCs) where the carbon filler and the matrix form an interpenetrating structure, contrary to particle filled systems. Aerographite networks with densities ranging from 3.0 to 13.9 mg/cm3 were produced in a chemical vapour deposition (CVD) process. An infiltration with epoxy leads to Aerographite/epoxy composites with filler contents in the range of 0.26–1.24 wt%. Their electrical conductivity is in the range of 2–13.6 S/m, thus, orders of magnitude higher compared to CNT-based PNCs at comparable filler contents. Although a large amount of direct interconnections of the graphitic tubes is given, interestingly the Aerographite/epoxy composites show a piezoresistive behaviour comparable to PNCs filled with carbon nanotubes (CNT) or graphene. Unexpected shifts between external mechanical strain and electrical signal have been observed in incremental piezoresistive experiments. Young's moduli and tensile strengths of the PNCs are not affected by embedding Aerographite networks. Fractographic observations identify graphitic wall slippage as the dominating failure mechanism. Both, piezoresistive characterization and fractography studies have been correlated and a model for the observed piezoresistive response is derived.Publicationtype: Journal Article74 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A tunable scaffold of microtubular graphite for 3D cell growth(Soc., 2016-06-03); ; ; ; Aerographite (AG) is a novel carbon-based material that exists as a self-supportive 3D network of interconnected hollow microtubules. It can be synthesized in a variety of architectures tailored by the growth conditions. This flexibility in creating structures presents interesting bioengineering possibilities such as the generation of an artificial extracellular matrix. Here we have explored the feasibility and potential of AG as a scaffold for 3D cell growth employing cyclic RGD (cRGD) peptides coupled to poly(ethylene glycol) (PEG) conjugated phospholipids for surface functionalization to promote specific adhesion of fibroblast cells. Successful growth and invasion of the bulk material was followed over a period of 4 days.Publicationtype: Journal ArticleScopus© Citations 24 295 408 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Electrical and thermal conductivity of aerogel/epoxy compositesThis study investigates the electrical and thermal characteristics of two novel carbon aerogel composites containing Aerographite (AG) and a CNT foam. Aerographite of densities between 3 to 16 mg/cm3, and the CNT foam with densities of 17 and 31 mg/cm3 were prepared in the CVD process. Both aerogels were infiltrated with epoxy resin using a vacuum assisted infiltration technique that preserves the interconnected structure. The neat Aerographite showed a maximum electrical conductivity of 10.3 S/m while the CNT foam reached 1.7 S/m. In the epoxy composites the electrical conductivity of the neat materials is adopted, thus resulting in an enhancement of orders of magnitude when compared to neat epoxy. Thermal conductivity was studied using a Xenon flash method. First results show an improvement of thermal conductivity of the composite by 33 % at the low filler content of only 0.26 wt.-% for the Aerographite and of 91 % for the CNT foam at 2.7 wt.-% filler content.Publicationtype: Conference Paper70