- Comparative Characterization of Multiscale Carbon Fiber Composite with Long and Short MWCNTs at Higher Weight Fractions
Michael Zimmer*, Qunfeng Cheng, Shu Li, James Brooks, Richard Liang, Ben Wang, and Chuck Zhang
J. Nanomater., 2012, 532080. DOl: 10.1155/2012/532080
AbstractThere are documented advantages to using carbon nanotubes (CNTs) in composites for various property enhancements. However, to date, only limited studies have been conducted on using of longer CNTs over 1 mm in length. This study used long multiwalled carbon nanotubes (LMWCNTs) and their longer extended networks to test multiple properties in thermal conductivity, electrical conductivity, mechanical strength, and modulus and then compared these properties to those of shorter multi-walled carbon nanotubes (SMWCNTs). For carbon fiber-reinforced composites, the longer graphite paths from LMWCNTs in the matrix were expected to improve all properties. The longer networks were expected to allow for more undisturbed phonon transportation to improve thermal conductivity. This in turn relates to improved electrical conductivity and better mechanical properties. However, results have shown that the LMWCNTs do not improve or decrease thermal conductivity, whereas the shorter MWCNTs provide mixed results. LMWCNTs did show improvements in electrical, mechanical, and physical properties, but compared to shorter MWCNTs, the results in other certain properties varied. This perplexing outcome resides in the functioning of the networks made by both the LMWCNTs and shorter MWCNTs.
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- Preform-based toughening technology for RTMable high-temperature aerospace composites
Xiao-Su Yi*, Qunfeng Cheng, and Zhizhen Liu
Sci. China-Technol. Sci., 2012, 55, 2255-2263. DOI: 10.1007/s11431-012-4949-8
AbstractThis article describes the efforts that led to the development of surface-loaded preforms that may be used to significantly improve the compression-after-impact strength of high-temperature composites and correspondingly to dramatically reduce the area of damage because of impact. Moreover, by matching the toughening polymer surface-loaded and design of the surface pattern, in-plane mechanical properties are unaffected or even improved over laminates made from the identical materials. The proprietary preforms, so-called ES™-Fabrics, may be handled and infused with the high-temperature RTMable resins such as bismaleimide and polyimide in exactly the same manner as traditional fabrics without surface modification. The RTM conditions for the preform-based toughening is fully compatible with the traditional process procedure, making the technology cost-effective in production. This technology represents a key enabler for the use of low-cost RTM processes for high-temperature resins to supplant prepreg as the building-block material of choice for aeronautical composite structures.
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- Thermal conductivity of MWCNT/epoxy composites: The effects of length, alignment and functionalization
Jin Gyu Parka*, Qunfeng Cheng, Jun Lu, Jianwen Bao, Shu Lia, Ying Tian, Zhiyong Liang*, Chuck Zhang, and Ben Wang
Carbon, 2012, 50, 2083-2090. DOI: 10.1016/j.carbon.2011.12.046
AbstractCarbon nanotubes (CNTs) show great promise to improve composite electrical and thermal conductivity due to their exceptional high intrinsic conductance performance. In this research, long multi-walled carbon nanotubes (long-MWCNTs) and its thin sheet of entangled nanotubes were used to make composites to achieve higher electrical and thermal conductivity. Compared to short-MWCNT sheet/epoxy composites, at room temperature, long-MWCNT samples showed improved thermal conductivity up to 55 W/mK. The temperature dependence of thermal conductivity was in agreement with κ ∝ Tn (n = 1.9-2.3) below 150 K and saturated around room temperature due to Umklapp scattering. Samples with the improved CNT degree of alignment by mechanically stretching can enhance the room temperature thermal conductivity to over 100 W/mK. However, functionalization of CNTs to improve the interfacial bonding resulted in damaging the CNT walls and decreasing the electrical and thermal conductivity of the composites.
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- In situ characterization of structural changes and the fraction of aligned carbon nanotube networks produced by stretching
Shu Lia, Jin Gyu Park, Zhiyong Liang*, Theo Siegrist, Tao Liu, Mei Zhang, Qunfeng Cheng, Ben Wang, and Chuck Zhang
Carbon, 2012, 50, 3859-3867. DOI: 10.1016/j.carbon.2012.04.029
AbstractThe mechanism of carbon nanotube (CNT) alignment during stretching was examined by the in situ characterization of carbon nanotube networks (CNTNs) under tensile strains using X-ray and Raman scattering techniques. A method of quantifying the inhomogeneous alignment of macroscopic CNTNs is explored based on bulk property measurements of their electrical anisotropy and X-ray diffraction diagrams. The results show that the process of stretch-induced alignment of CNTNs included straightening the waviness of the long nanotube ropes, as well as the self-assembling and denser packing of the nanotubes. For samples at a strain of 40%, the fraction of aligned nanotubes was as high as 0.85. The aligned fraction of CNTs serves as an important parameter for the quality control of the alignment process and numerical simulations of structure–property relationships of CNTNs and their composites.
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- The fabrication of single-walled carbon nanotube/polyelectrolyte multilayer composites by layer-by-layer assembly and magnetic field assisted alignment
Ying Tian, Jin Gyu Park, Qunfeng Cheng, Zhiyong Liang*, Chuck Zhang, and Ben Wang
Nanotechnology, 2009, 20, 335601. DOI: 10.1088/0957-4484/20/33/335601
AbstractSingle-walled carbon nanotube (SWNT)/polymer composites are widely studied because of their potential for high mechanical performance and multifunctional applications. In order to realize highly ordered multilayer nanostructures, we combined the layer-by-layer (LBL) assembly method with magnetic force-induced alignment to fabricate SWNT/poly(ethylamine) (PEI) multilayer composites. The SWNTs were functionalized with the anionic surfactant sodium dodecylbenzenesulfonate (NaDDBS) to realize negative charge at pH>7, while the PEI is positively charged at pH<7. The LBL method is based on the electrostatic absorption between the charged SWNTs and PEI resin to form multilayer composites on a solid substrate polydimethylsiloxane. Since the fabricated thickness of each SWNT-NaDDBS/PEI bilayer is uniform (~150 nm), the multilayer film thickness can be strictly controlled via the number of deposition cycles. A high magnetic field (8.5 Tesla) was used to align the SWNTs during the LBL process. The resultant LBL composite samples demonstrated high SWNT loading of approximately 50 wt% and uniform distribution of SWNTs in the multilayer structures, which was verified using a quartz crystal microbalance. Good alignment was also realized and observed through using high magnetic fields to align the nanotubes during the LBL deposition process. The results indicate that the LBL/magnetic alignment approach has potential for fabricating nanotube composites with highly ordered nanostructures for multifunctional materials and device applications.
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- Electromagnetic interference shielding properties of carbon nanotube buckypaper composites
Jin Gyu Park*, Jeffrey Louis, Qunfeng Cheng, JianwenBao, Jesse Smithyman, Richard Liang,Ben Wang, Chuck Zhang, James S Brooks, Leslie Kramer, Percy Fanchasis, and David Dorough
Nanotechnology, 2009, 20, 415702. DOI: 10.1088/0957-4484/20/41/415702
AbstractPreformed carbon nanotube thin films (10-20 µm), or buckypapers (BPs), consist of dense and entangled nanotube networks, which demonstrate high electrical conductivity and provide potential lightweight electromagnetic interference (EMI) solutions for composite structures. Nanocomposite laminates consisting of various proportions of single-walled and multi-walled carbon nanotubes, having different conductivity, and with different stacking structures, were studied. Single-layer BP composites showed shielding effectiveness (SE) of 20-60 dB, depending on the BP conductivity within a 2-18 GHz frequency range. The effects on EMI SE performance of composite laminate structures made with BPs of different conductivity values and epoxy or polyethylene insulating layer stacking sequences were studied. The results were also compared against the predictions from a modified EMI SE model. The predicted trends of SE value and frequency dependence were consistent with the experimental results, revealing that adjusting the number of BP layers and appropriate arrangement of the BP conducting layers and insulators can increase the EMI SE from 45 dB to close to 100 dB owing to the utilization of the double-shielding effect.
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- Morphological and Spatial Effects on Toughness and Impact Damage Resistance of PAEK-toughened BMI and Graphite Fiber Composite Laminates
Qunfeng Cheng, Zhengping Fang, Yahong Xu, and Xiao-Su Yi*
Chin. J. Aeronaut., 2009, 22, 87-96. DOI: 10.1016/S1000-9361(08)60073-4
AbstractThe microstructure property relationships have been studied in terms of glass transition behavior, phase morphology, and fracture toughness on thermoplastic polyetherketone with a phenolphthalein side group (PAEK) toughened bismaleimdes (BMI) resins, and in terms of interlaminar morphology and compression after impact (CAI) on the graphite fiber (T700SC), the reinforced BMI matrix composites that are toughened with a so-called ex-situ concept, respectively. The characteristic morphology spectrum has been found to occur as the concentration of PAEK is varied. In particular, the relationship between the morphology and the fracture toughness has been explored on the PAEK-BMI blends. The fracture micromechanism has then been used to explain the delamination and impact damage behavior on the graphite laminated systems, where the morphology properties relationship held true. The complex nature of the diffusion-controlled phase behavior has also qualitatively been studied, which served as a model for understanding the ex-situ toughening concept.
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- High Mechanical Performance Composite Conductor: Multi-Walled Carbon Nanotube Sheet/Bismaleimide Nanocomposites
Qunfeng Cheng, Jianwen Bao, JinGyu Park, Zhiyong Liang*, Chuck Zhang, and Ben Wang
Adv. Funct. Mater., 2009, 19, 3219-3225. DOI: 10.1002/adfm.200900663
AbstractMulti-walled carbon nanotube (MWNT)-sheet-reinforced bismaleimide (BMI) resin nanocomposites with high concentrations (~60 wt%) of aligned MWNTs are successfully fabricated. Applying simple mechanical stretching and prepregging (pre-resin impregnation) processes on initially randomly dispersed, commercially available sheets of millimeter-long MWNTs leads to substantial alignment enhancement, good dispersion, and high packing density of nanotubes in the resultant nanocomposites. The tensile strength and Young’s modulus of the nanocomposites reaches 2088 MPa and 169 GPa, respectively, which are very high experimental results and comparable to the state-of-the-art unidirectional IM7 carbon-fiber-reinforced composites for high-performance structural applications. The nanocomposites demonstrate unprecedentedly high electrical conductivity of 5500 S cm−1 along the alignment direction. Such unique integration of high mechanical properties and electrical conductance opens the door for developing polymeric composite conductors and eventually structural composites with multifunctionalities. New fracture morphology and failure modes due to self-assembly and spreading of MWNT bundles are also observed.
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