Nanotube discontinuity

ZrS2 nanotubes admixed with nanorods have been prepared by the thermal decomposition of ZrS, under H2 + Aral 1170 K..M Many of the nanotubes exhibit rectangular tips. The inner wall of some of the ZrS2 nanotubes show non-uniformity near the tip resulting from the discontinuous growth of the ZrS2 layers. 

Fig. 7 (A) Carbon nanotube exposed at the breakage edge of a VGCF as (A) grown and (B) heat-treated at 3000 C. The sample is fractured by pulverization and the core diameter is 50 A. (B) These photos suggest a structural discontinuity between the nanotube core of the fiber and the CVD deposited carbon layers. The images show the strong mechanical properties of the nanotube core, which maintains its form after breakage of the periphery. (From Ref...

Laser assisted chemical vapor deposition (LCVD) yields continuous or discontinuous low diameter fibers directly from the vapor phase by tip growth. Chemical vapor deposition (CVD) on the surface of a small diameter, preferably sacrificial, precursor fiber yields a large diameter fiber or microtube. Chemical vapor infiltration (CVI) can change the chemistry of precursor fibers by infiltration of a chemically reactive vapor species. Finally, laser vaporization (LV) of carbon-metal mixtures yields highly entangled mats of nearly endless nanotube ropes. 

On the other hand, CNTs possess one of the highest thermal conductivities, which can be exploited to fabricate thermally conductive nauocomposites [8,9]. This chapter wiU focus on the applications of CNTs as discontinuous reinforcement for polymer matrices, which includes fabrication methods, morphologies and mechanical properties of the carbon nanotubes reinforced polymer nanocomposites. 

Fiber-reinforced polymer composites can contain short, discontinuous fibers (usually in thermoplastics see Fig. 1.14) or long, continuous fibers in thermoset resins. Fibers can vary from the usual glass fibers with thicknesses of some tens of micrometers up to nanofibers or carbon nanotubes (single-waiied or multiwalled, SWCNT or MWCNT) about 10 nm thick. The properties of fiber-reinforced composites depend on thickness, length, and volume content of the fibers, as well as on adhesion (interfacial strength) and matrix properties. 

It is well known that the electrical conductivity of polymers loaded with conductive fillers, such as carbon black (CB), graphite particles (GPs), carbon nanotubes (CNTs), and metallic particles, exhibits a discontinuous increase with the filler loading. The phenomenon is explained in terms of the percolation theory [27]. When the concentration of the conductive filler reaches a critical value, termed the percolation threshold, a conductive path is formed in the composite along with a sudden jump in the electrical conductivity by several orders of magnitude [27]. However, even with this jump the conductivity obtained is still too low for bipolar plate applications. As such, filler concentrations much higher than the percolation threshold are required to raise the conductivity to the level suitable for bipolar plate applications [18-23]. Unfortunately, the conductivity derived in this way is obtained at the expense of processability and thus increases the manufacturing cost of bipolar plates. 

It has been shown that, when using fiber-reinforced polymers, the maximum amount of fibers in the matrix is about 70 vol%. In practice, the fiber volume firactions in these materials vary between 20 and 60%. Let a volume element of 1 cm be reinforced with discontinuous fibers with 10 pm diameter, particles (e.carbon nanotubes (CNT) with 10 nm diameter-. The aspect ratios are generally expected to be 20, 100, and 1000, respectively. If it is further assumed that a volume content of 30% exists for both the fibers and the particles, and only 3% for the nanotubes, the results are quite interesting - the filler element numbers become -10 fibers, -10 pai-ticles and -10 nanotubes. The siuface areas amount to -0.1 m for the... 

A thermoplastic EPDM/iPP vulcanizate consists of a continuous and thermoplastic iPP phase, which forms the minority of this blend (ca. 20 wt%), and a cross-linked, oil-extended, dispersed EPDM phase (ca. 80 wt%). The discrete EPDM phase consists of submicron or several microns size particles. Within the discontinuous EPDM/ iPP vulcanizate morphology, the cross-linked EPDM phases act as excluded volumes into which carbon nanotubes can hardly penetrate during melt-blending, or after performing the four steps of the latex concept, described in depth in earlier chapters of this book. 

Zhang, H. Zhang, X. Wu, T. Zhang, Z. Zheng, 1. Sun, H. Template-based synthesis and discontinuous hysteresis loops of cobalt nanotube arrays. J. Mater. Sci. 2013, 48, 7392-7398. 

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