Conductive microfibril

Based on the discussion above, it is clear that the amount and distribution of the CB particles on the surface of microfibrils are very critical factors to determine the percolation threshold of i-CB/PET/PE composite. When the CB content in the PET phase is just beyond the percolation threshold of CB/PET compound, the continuous network of CB particles may be formed inside the microfibrils. However, there are hardly any CB particles on the surface of the CB/PET microfibrils and there exists a pure polymer layer below the surface of CB/PET microfibrils. This results in a high contact resistance among the microfibrils. The whole system exhibits an insulator state though the electrically conductive microfibrils may form a network. As the CB content in the CB/PET microfibrils reaches max> fhe number of CB paxticles on the surface evidently increases. Conduction pathways axe formed between some contact points in the microfibril network. With a further increase of CB content, the amount of CB particles on the microfibril surface increased significantly, and the electrically conductive contact points also increased. When the number of contact points is large enough to form a network to sustain the electron transmission in the whole... 

Zhang Y C, Dai K, Pang H, Luo Q J, Li Z M and Zhang W Q (2011) Temperature and time dependence of electrical resistivity in an anisotropicaUy conductive polymer composite with in situ conductive microfibrils, J Appl Polym Sci (in press). 

The same authors 369,3701 also obtained similar results if the liquid crystal solvent was aligned by flow during the polymerization. They showed that the polymerization conditions lead to alignment of the fibrils within the polymer mass and of the chains within the fibrils polymers produced in this way could also be doped to a conductivity of 104 S cm-1 371). The morphology of polyacetylene produced by polymerization in a liquid crystal solvent, aligned both magnetically and by flow, has been studied by Montaner et al. 371). They show that the polymer film is made up of very long fibrils built from microfibrils. In one fibril, the orientation of microcrystalline domains with respect to the fibril axis is very well defined, whilst the orientation of the different fibrils in the sample spreads over 20°. 

These constitute the basic elements of the fibers and are responsible for its rigidity. The cellulose microfibrils, however, are not totally crystalline but rather contain amorphous regions which are accessible to water molecules. Water does not penetrate the crystalline region. The total water content of a whole fiber and its distribution within the fiber is a function of the relative amount of amorphous material, the presence of lignins, which are hydrophobic, and the presence of hemicelluloses which are hydrophilic. The total water content of a whole fiber will affect the conductivity by allowing an increased effective ionic mobility. 

At the early stage of research on in situ composites, most work has been conducted on the LCP microfibril formation connected with the melt viscosity or viscosity ratio, composition, and flow mode, etc. These results have been summarized and reviewed by several researchers [11-17]. In the aspect of flb-rillation, the current work is only a supplement to those reviews, with additional new insights and results. We will summarize and review the recent work on the compatibility of LCP blends in this chapter. 

Microfibril Reinforced Polymer-Polymer Composite via Hot Stretching Electrically Conductive Functionalization... 

Usually, a composite filled with large specific ratio fibers or flakes has a lower percolation threshold than that filled with spherical conductive particles. The fillers with a high aspect ratio may also increase the tendency to form the co-continuous phases in polymer blend matrices [10]. These morphology-property relationships imply that if the conductive filler is preferential, or even totally localized in the minor phase or its surface (a-polymer) of a polymer blend, and the conductive filler/a-polymer blend is elongated or oriented to form conductive in situ microfibrils in the polymer matrix ([3-polymer), the composite obtained may have high conductivity (construction of 3D conductive in situ microfiber... 

From this view, the authors have used a new approach called melt extrusion-hot stretching-quenching to prepare two categories of CPC (isotropic and anisotropic CPC) based on in situ microfibril reinforced polymer-polymer composites. This chapter briefly describes our recent work on several conductive in situ microfibrillar reinforced composites via hot stretching. 

The distance between conductive fillers is of great importance for electric conduction in the filled conductive polymer composite. It is widely accepted that the electrons can transmit or jump between the conductive fillers in the presence of an electric field, even if there is a gap between the fillers. However, this gap cannot be too large and is usually accepted to be lower than 10 nm. Thus, the distance between the outmost CB particles in one microfibril and those in another microfibril is a crucial factor for electric conduction between two microfibrils. Figure 13.5 shows the SEM micrographs of the cryofractured... 

Figure 13.8. The schematic illustration of microstructural development for the conductive microfibrillar network during thermal process. The gray and the black regions represent the cross sections of microfibrils and the CB aggregates, respectively, (a) At room temperature before heating (b) beyond the PTC region (c) after isothermal treatment at high temperature (d) cooling to room temperature again [19]...

In this section, we attempt to suppress the influence of the to reduce the percolation threshold by localizing CB particles in the surfaces of in situ microfibrils [22]. When the conductive filler, a-polymer and /3-polymer are CB, PET and PE, we can obtain isotropic o-CB/PET/PE composites through preparation procedures in Figure 13.1. 

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