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Study On Mechanical Properties Of Double-walled Carbon Nanotube Macrostructures And Relative Composites

Posted on:2006-07-10Degree:MasterType:Thesis
Country:ChinaCandidate:Y J LiFull Text:PDF
GTID:2121360182983402Subject:Materials Science and Engineering
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Carbon nanotubes (CNTs) are proved to possess remarkable mechanicalproperties by both simulations and experiments, which gives them potential asstructural material and reinforcement in composites. Double-walled carbon nanotube(DWNT) is a critical type of one-dimensional material between single-walled carbonnanotube (SWNT) and multi-walled carbon nanotube (MWNT), yet there is still noexperimental data on its mechanical properties by now. In this dissertation,mechanical properties of macroscopic DWNT strands and films are studied aftersynthesis, and systematic research is also made for relative one-to-three-dimensionalcomposites. Tensile experiments were made on aligned DWNT strands with lengths of ~10cm synthesized by chemical vapor deposition (CVD) method using xylene as carbonsource. Their average tensile strength and Young's modulus are 1.2 GPa and 16 GPa,respectively. For DWNT bundles which were actually loaded, their average strengthand modulus increase to 6 GPa and 80 GPa, with specific values of 4.9 GPa and 56GPa, respectively, indicating excellent mechanical properties of DWNT strands. Composite fibers and films were made using solution mixing method by soakingas-grown DWNT strands and films in epoxy/acetone solutions. Mechanical propertiesof the composites approximately increase as the concentration of the soakingsolutions decreases. At the concentration of 10 vol%, the average tensile strength andYoung's modulus of the composite fibers increase by 25% and 69% compared withoriginal DWNT strands, respectively, while the factors are 4.4 and 3.3 for compositefilms, respectively. Since load can be transferred by polymer in composites, DWNTbundles are more uniformly loaded in composites than in original productions. At theconcentration of 2 wt%, the average compressive strength and modulus of layer-likeepoxy matrix composite bulks increase by 49% and 18% compared with the matrix,respectively, while the tensile strength decreases slightly. It was found that polymer matrixes with different percentage of elongationexert different strengthening effects on DWNT strands. Epoxy resin, whosepercentage of elongation is close to that of DWNT strands, has better enhancingeffect on mechanical properties of DWNT strands than brittle polystyrene. Themorphology of DWNT bundles can also affect the mechanical properties ofcomposites. For those disordered short bundles, their relative composites have poormechanical properties.Raman spectroscopy revealed that the D* band of DWNTs shifts to lowerfrequencies after tensile tests of the composites, while the band shifts to higherfrequencies after compression, indicating that load can be effectively transferred frompolymer matrix to CNTs through interfacial shear stress. Changes were also found inthe band shape. The D* band of DWNTs leans to low frequency side and highfrequency side in tensile stress and compressive stress, respectively. This indicates thesymmetry of D* band can also be a supplementary tool in judging the stress status ofCNTs besides shifting of this band.
Keywords/Search Tags:double-walled carbon nanotube, mechanical properties, composite, interfacial bonding, Raman spectroscopy
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