Mecklenburg, Matthias

In 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 model

This 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.

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