Christine Täschner

Melt Mixing as Method to Disperse Carbon Nanotubes into Thermoplastic Polymers

Abstract This paper presents melt mixed composites where two ways of introducing nanotubes in polymer matrices were used. In the first case, commercially available masterbatches of nanotube/polymer composites are used as the starting materials that are diluted by the pure polymer in a subsequent melt mixing process (masterbatch dilution method) while in the other case nanotubes are directly incorporated into the polymer matrix. As an example of the masterbatch dilution method, composites of polycarbonate with MWNT are presented which are produced using a Brabender PL‐19 single screw extruder. In this system, electrical percolation was found at about 0.5 wt% MWNT. The nanotube dispersion as observed by TEM investigations is quite homogeneous. The direct incorporation method is discussed in composites of polycarbonate with MWNT and SWNT. For commercial MWNT percolation was found between 1.0 and 3.0 wt% depending on the aspect ratio and purity of the materials. For HiPCO‐SWNT from CNI percolation occurred between 0.25 wt% and 0.5 wt% SWNT. The incorporation of nanotubes significantly changes the stress‐strain behavior of the composites: modulus and stress are enhanced; however, the elongation at break is reduced especially above the percolation concentration.

Carbon nanotubes terminated with hard magnetic FePt nanomagnets

The advancement in carbon nanotube (CNT) technology includes significant interest in their functionalization to modify their chemical and physical properties. In particular, the selective functionalization of the CNT ends opens exciting opportunities to design nanoscale architectures and networks. The realization of hard-magnetically terminated CNT via plasma enhanced chemical vapor deposition from Fe–Pt thin films is reported. Although FePt is rarely used as a catalyst for CNT synthesis the said binary catalyst affords attractive hard magnetic properties when present in the chemically ordered L10 phase.

Surface modification of polytetrafluoroethylene with tetraethoxysilane by using remote argon/dinitrogen oxide microwave plasma

The use of remote microwave plasma for the polymerization and deposition of tetraethoxysilane on the surface of polytetrafluoroethylene was investigated using a mixture of Argon and dinitrogen oxide as carrier gas. Layers with thicknesses of 0.5-3 μm were obtained, differing in chemical composition, surface energy, and flexibility/ brittleness, depending on the plasma power and both the treatment and aging times. In general, milder treatments and shorter aging times resulted in higher contents of organic structural elements in the layers and greater flexibility and surface energy. Anchoring between the layers and the bulk polytetrafluoroethylene was at least partially caused by fibrils interconnecting the two components. These results were obtained by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy in the attenuated total reflection mode, contact angle measurements, and scanning electron microscopy combined with energy dispersive X-ray analysis.

Effect of substrate material on the growth and field emission characteristics of large-area carbon nanotube forests

Carbon nanotubes (CNTs) are a promising replacement for tungsten filaments as electron emitters in conventional x-ray sources, owing to their higher aspect ratio, superior mechanical stability, chemical inertness, and high electrical and thermal conductivities. Conditions for realizing the best emission behavior from CNTs have been formulated over the last few years. In this paper, we report the relatively less-investigated factor, namely, the influence of the nature of substrate material on the growth as well as field emission characteristics of large-area multiwalled CNTs for their practical application in medical x-ray sources. We compare the morphology of CNTs on a variety of substrates such as stainless steel, copper, molybdenum, graphite, few-layer graphene, and carbon nanowalls grown by thermal chemical vapor deposition following a simple drop-coating of catalyst. We find that CNTs grown on stainless steel and graphite show the best combination of emission characteristics under pulsed operation mod...

Synthesis and characterization of carbon nanotubes

The catalytic chemical vapor deposition (CCVD) is a very promising process with respect to large scale production of different kinds of carbon nanostructures. By modifying the deposition temperature, the catalyst material and the hydrocarbon nanofibers with herringbone structure, multi-walled nanotubes with tubular structure and single-walled nanotubes were deposited. Furthermore, layers of aligned multi-walled nanotubes could be obtained on oxidized silicon substrates coated with thin sputtered metal layers (Co, permalloy) as well as onto WC-Co hardmetals by using the microwave assisted plasma CVD process (MWCVD). The obtained carbon modifications were characterized by scanning (SEM) and transmission (TEM) electron microscopy. The hydrogen storage capability of the nanofibers and nanotubes and the electron field emission of the nanotube layers was investigated.