Evaluation and identification of electrical and thermal conduction mechanisms in carbon nanotube/epoxy composites (original) (raw)
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Thermal and electrical conductivity of single- and multi-walled carbon nanotube-epoxy composites
Composites Science and Technology, 2006
The electrical and thermal conductivities of epoxy composites containing 0.005-0.5 wt% of single-walled (SWNTs) or multi-walled (MWNTs) carbon nanotubes have been studied. The MWNT composites had an electrical percolation threshold of <0.005 wt%, whereas the thermal conductivity of the same samples increased very modestly as a function of the filler content. In the case of the SWNT composites, the electrical percolation thresholds were higher (0.05-0.23 wt%) whereas the thermal conductivity was lower than that of the pristine epoxy.
Journal of Applied Polymer Science, 2008
Multiwalled carbon nanotube/epoxy composites loaded with up to 0.5 wt % multiwalled carbon nanotubes were prepared and characterized. Infrared microscopy, scanning electron microscopy, thermogravimetry, differential scanning calorimetry, thermomechanical analysis, and electrical conductivity measurements of the composites were performed. Infrared microscopy and scanning electron microscopy images showed that the debundled nanotubes were well dispersed. The thermal expansion coefficients, before and after the glass transition, remained approximately constant with the addition of nanotubes, whereas the electrical conductivity at room temperature increased approximately 5 orders of magnitude. This result was attributed to the thermal expansion coefficients of the intertube gap on the carbon nanotube bundles, which were in the same range as that of the epoxy resin. Therefore, nanocomposites capable of electrostatic dissipation can be processed as neat epoxy materials with respect to the volume changes with temperature. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
2022
Carbon nanotubes (CNT) are promising materials due to their outstanding mechanical and electrical properties. However, the electrical percolation threshold obtained in epoxy/carbon nanotube (CNT) nanocomposites is one of the lowest among conductive nanocomposites. There exist research efforts to improve the electrical percolation threshold of epoxy/CNT with the addition of silver nanoparticles. The aim of this novel work is to use biosynthesized silver nanoparticles (GAg.NPs) as a replacement for high-cost Ag.NPs for the enhancement of the electrical properties of epoxy/CNT. The nanocomposites were produced by using 0.1, 0.2, 0.3, 0.4 and 0.5% CNTs and 0.5% GAg.NPs in the epoxy matrix. The morphology, electrical conductivity and thermomechanical properties of the developed composites were determined. The results show an increment in the electrical conductivity and storage modulus of the epoxy/CNT with the addition of GAg.NPs. The work established that the addition of GAg.NPs to epoxy-CNT can be used to improve electrical conductivity and storage modulus of epoxy-CNT composites for electronic applications.
Thermal conductivity and interfacial resistance in single-wall carbon nanotube epoxy composites
Applied Physics Letters, 2005
We report thermal conductivity measurements of purified single-wall carbon nanotube (SWNT) epoxy composites prepared using suspensions of SWNTs in N-N-Dimethylformamide (DMF) and surfactant stabilized aqueous SWNT suspensions. Thermal conductivity enhancement is observed in both types of composites. DMF-processed composites show an advantage at SWNT volume fractions between ϕ∼0.001 to 0.005. Surfactant processed samples, however, permit greater SWNT loading and exhibit larger overall enhancement (64±9)% at ϕ∼0.1. The enhancement differences are attributed to a ten-fold larger SWNT/solid-composite interfacial thermal resistance in the surfactant-processed composites compared to DMF-processed composites. The interfacial resistance is extracted from the volume fraction dependence of the thermal conductivity data using effective medium theory. [C. W. Nan, G. Liu, Y. Lin, and M. Li, Appl. Phys. Lett. 85, 3549 (2004)].
Journal of Polymer Science Part B-polymer Physics, 2011
We report on the effect of processing conditions on rheology, thermal and electrical properties of nanocomposites containing 0.02-0.3 wt % multiwall carbon nanotubes in an epoxy resin. The influence of the sonication, the surface functionalization during mixing, as well as the application of external magnetic field (EMF) throughout the curing process was examined. Rheological tests combined with optical microscopy visualization are proved as a very useful methodology to determine the optimal processing conditions for the preparation of the nanocomposites. The Raman spectra provide evidence for more pronounced effect on the functionalized with hardener compositions, particularly by curing upon application of EMF. Different chain morphology of CNTs is created depending of the preparation conditions, which induced different effects on the thermal and electrical properties of the nanocomposites. The thermal degradation peak is significantly shifted towards higher temperatures by increasing the nanotube content, this confirming that even the small amount of carbon nanotubes produces a strong barrier effect for the volatile products during the degradation. The ac conductivity measurements revealed lower values of the percolation threshold (pc) in the range of 0.03-0.05 wt %. CNTs for the nanocomposites produced by preliminary dispersing of nanotubes in the epoxy resin, compared to those prepared by preliminary functionalization of the nanotubes in the amine hardener. This is attributed to the higher viscosity and stronger interfacial interactions of the amine hardener/CNT dispersion which restricts the reorganization of the nanotubes. The application of the EMF does not influence the pc value but the dc conductivity values (r dc) of the nanocomposites increased at about one order of magnitude due to the development of the aforementioned chain structure. V
Applied Physics A
For a thermoelectric application, the thermal conductivity, electrical conductivity and figure of merit of epoxy resin-based composites incorporated with carbon nanotubes and TiO 2 are investigated in this paper. First, the composite is prepared with a solution blending method. Then, the structure, thermal and electrical conductivities are characterized with experimental methods. Finally, the thermal conductivity, electrical conductivity and figure of merit are discussed. Results turn out that with an increasing content of carbon nanotube fillers, there are different changing trends of thermal and electrical conductivities because of large difference between thermal and electrical contact resistances in the composite. With the increasing filler content, the electrical conductivity increases exponentially while thermal conductivity saturates to be a constant value. Due to the large ratio of electrical to thermal conductivities, the figure of merit with 8 wt% of fillers is more than 50 times larger than that with a low content of fillers. Our results confirm that the recently proposed concept of 'electron-percolation thermal-insulator' is a feasible way to enhance the figure of merit of a polymer composite.
Carbon, 2011
The effect of the functionalization of multi-wall carbon nanotubes (MWCNTs) on the structure, the mechanical and electrical properties of composites was investigated. Samples based on epoxy resin with different weight percentage of MWCNTs or COOH-functionalized carbon nanotubes (MWCNT-COOH) were prepared and characterized. Dynamicmechanical thermal analysis shows that the storage modulus increases with the addition of MWCNTs, whereas a constant value or even a weak reduction was observed for functionalized nanotubes. Two phases were suggested in the composites with MWCNT-COOH, both by dynamic-mechanical properties and by water transport. Chemical functionalization of MWCNTs increases the compatibility with the epoxy matrix due to the formation of an interface with stronger interconnections. This, in turn, causes a significant decrease in the electrical conductivity of this type of composite with respect to the untreated MWCNTs which can be explained in terms of tunnelling resistance between interacting nanotubes.
Electrical conductivity of chemically modified multiwalled carbon nanotube/epoxy composites
Carbon, 2005
The electrical conductivity of oxidized multiwalled carbon nanotubes (MWNT)/epoxy composites is investigated with respect to the chemical treatment of the MWNT. The oxidation is carried out by refluxing the as-received MWNT in concentrated HNO 3 and H 2 O 2 /NH 4 OH solutions, respectively, under several different treatment conditions. The oxidized MWNT are negatively charged and functionalized with carboxylic groups by both solutions. The MWNT oxidized under severe conditions are well purified, but their crystalline structures are partially damaged. It is recognized that the damage to the MWNT has considerable influence on the electrical properties of the MWNT composites, causing the electrical conductivity to be lowered at a low content of MWNT and the percolation threshold to be raised. The MWNT oxidized by the mixture of H 2 O 2 and NH 4 OH solution provides epoxy composites with a higher conductivity than those produced with the MWNT oxidized by nitric acid over the whole range of MWNT, independently of the oxidation conditions.
Electrical and mechanical properties of carbon nanotube‐epoxy nanocomposites
Journal of Applied Polymer …, 2010
In this work, electrical conductivity and thermo-mechanical properties have been measured for carbon nanotube reinforced epoxy matrix composites. These nanocomposites consisted of two types of nanofillers, single walled carbon nanotubes (SW-CNT) and electrical grade carbon nanotubes (XD-CNT). The influence of the type of nanotubes and their corresponding loading weight fraction on the microstructure and the resulting electrical and mechanical properties of the nanocomposites have been investigated. The electrical conductivity of the nanocomposites showed a significantly high, about seven orders of magnitude, improvement at very low loading weight fractions of nanotubes in both types of nanocomposites. The percolation threshold in nanocomposites with SW-CNT fillers was found to be around 0.015 wt % and that with XD-CNT fillers around 0.0225 wt %. Transmission optical microscopy of the nanocomposites revealed some differences in the microstructure of the two types of nanocomposites which can be related to the variation in the percolation thresholds of these nanocomposites. The mechanical properties (storage modulus and loss modulus) and the glass transition temperature have not been compromised with the addition of fillers compared with significant enhancement of electrical properties. The main significance of these results is that XD-CNTs can be used as a cost effective nanofiller for electrical applications of epoxy based nanocomposites at a fraction of SW-CNT cost.
2008
The incorporation of functionalized carbon nanotubes in a polymer matrix is expected to greatly enhance the physical and mechanical properties of the polymer due to inherent superior properties of carbon nanotubes (CNTs): high modulus and strength, high thermal stability and enhanced electrical conductivity. Nanocomposite materials based on epoxy polymer matrix and different types of functionalized carbon nanotubes were synthesized. The effect of CNTs on dynamic mechanical properties by DMA, on curing process by DSC and themostability by TGA and DTG were studied. The system based on diglycidylether of bisphenol A (DGEBA) cured with a polyetheramine (D230) and reinforced with amino-functionalized doublewall carbon nanotubes (DWNT-NH 2 ) showed lower T g values. SEM images reveal an enhance of dispersion if amino-functionalized CNTs are used.