2006 Fiscal Year Final Research Report Summary
Study on the polymer and conductive filler composites in terms of the tunnel mechanism
| Project/Area Number |
17550192
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Polymer/Textile materials
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| Research Institution | Nara Women's University |
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Principal Investigator |
BIN Yuezhen Nara Women's University, Graduate School of Humanities and Sciences, research associate, 大学院人間文化研究科, 助手 (90343269)
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| Project Period (FY) |
2005 – 2006
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| Keywords | PTC effect / electrical conductivity / percolation theory / tunnel mechanism / carbon fibers / carbon nanotubes / composite / gelation / crystallization |
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| Research Abstract |
The electrical conductivity of composites of polymer and conductive fillers generally obey percolation theory. However, as the carbon fibers or carbon nanotubes with high aspect ratios were used as filler, the composites usually derivate from percolation theory, especially the gelation/crystallization technique was used for preparing the composites. It is attributed to that the crystallization occurs on the filler surface and form a thin polymer layer, and the thickness of the polymer layer are influence the conductivity of composites due to the tunnel mechanism. In this research, several kinds of polymers, polyethylene, polypropylene, polyvinyl alcohol and polyimide, were adopted as matrix, and the carbon materials with different aspect ratios were used as fillers. Different preparation methods, such as gelation methid, in-situ polymerization, kneading method, were compared.
The composite gel films of ultrahigh molecular weight polyethylene (UHMWPE) and low molecular weight polyethylen
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e (LMWPE) filled with short carbon fibers were prepared by gelation/crystallization. The excellent positive temperature coefficient (PTC) effect was achieved. The analysis of AC electrical conductivity and dielectric permittivity was done. The dielectric behaviors of the interfacial polarization between polyethylene matrix and carbon fibers could be described by Maxwell-Wagner-Sillars relaxation.
UHMWPE-MWNTs composites prepared by gelation technique in decalin solutions could be elongated to more than 100-fold and the electrical conductivity were rarely influenced by elongation. But the percolation threshold was high and the maxmum value of conductivity is less than 1S/cm. However, for the composites prepared using paraffin as solvent. The resulting electrical properties show lower electrical percolation threshold, which is 1.4 vol %, than that of UHMWPE-MWNT composites prepared by gelation/crystallization from decalin solution. Good reproducibility and higher maximum of electrical conductivity are obtained. It is attributed the different crystallization behavior of UHMWPE on the surface of MWNTs.
Polyimide (PI)-carbon nanotubes composites were fabricated by in situ polymerization using MWNT as fillers. It suggested that in situ polymerization is an ideal technique to make a perfect dispersion of carbon nanotubes into matrixes. The results imply that the percolation threshold for the electric conductivity of the resultant Pl-MWNT composites was ca. 0.15 vol%. Less
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