Fraction Of Multi-walled Carbon Nanotubes Research Articles

Physical properties of nanocomposites prepared by in situ polymerization of high-density polyethylene on multiwalled carbon nanotubes

In situ metallocence polymerization was used to prepare nanocomposites of multiwalled carbon nanotubes (MWCNT) and high density polyethylene (HDPE). This polymerization method consists of attaching a metallocene catalyst complex onto the surface of MWCNT followed by surface-initiated polymerization to generate polymer brushes on the surface. All the procedures of polymerization made progress with one-pot process. The morphological observation of nanocomposites using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the nanotubes are uniformly dispersed throughout HDPE matrix. Physical properties of thermal and electrical conductivities and rheological response have been characterized. Since the carbon nanotubes are wrapped by PE molecules, the large interface provided by MWCNT's lead to strong phonon boundary scattering. Thus, the enhancement of thermal conductivity by the inclusion of nanotubes was quite restrictive. On the other hand, electrical conductivity and rheological properties show the property transition at the critical concentration of carbon nanotubes (percolation threshold). The DC conductivity increased with increasing weight fraction of MWCNT from 1.0 x 10(-13) S cm(-1) (neat HDPE) to 1.3 x 10(-2) S cm(-1) (HDPE/7.3 wt% of MWCNT) at room temperature and the electrical percolation threshold was ca. 7.3 wt%. The percolation threshold concentration of MWCNT for the rheological properties was ca. 8.7 wt%, similar to that of the electrical conductivity. Difference in the percolation behaviors between the MWCNT mixed nanocomposites and the PE-coated MWCNT nanocomposites is discussed in terms of the dispersion and the tube-tube distance of MWCNT.

Urea assisted hydroxyapatite mineralization on MWCNT/CHI scaffolds

Urea assisted hydroxyapatite (HAp) mineralization was performed on scaffolds composed of a major fraction of multiwall carbon nanotubes (MWCNT, 85 wt.%) and a minor one of chitosan (CHI, 15 wt.%). The MWCNT/CHI scaffolds were synthesized through a cryogenic process (so called ISISA, ice segregation induced self-assembly) that allowed the achievement of macroporous monoliths whose structure resembled a chamber-like architecture in the form of interconnected MWCNT/CHI sheets arranged in parallel layers crossed by pillars. The mineralized architectures were composed of flower like hydroxyapatite (HAp) crystalline clusters of ca. 1 µm, homogeneously distributed throughout the internal surface of the scaffold macrostructure. HAp mineralized MWCNT/CHI scaffolds were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR) and scanning and transmission electron microscopy (SEM and TEM, respectively). Calibrated energy dispersion X-ray spectroscopy (EDS) and selected-area electron diffraction (SAED) were also performed in the transmission electron microscope to further HAp characterization. Preliminary in vitro experiments demonstrated the suitability of HAp mineralized MWCNT/CHI scaffolds for bone tissue growth.

Multiwall carbon nanotube scaffolds for tissue engineering purposes

The use of scaffolds composed of a major fraction of multiwall carbon nanotubes (MWCNT, up to 89 wt.%) and a minor one of chitosan (CHI), and with a well-defined microchannel porous structure as biocompatible and biodegradable supports for culture growth is described. Cell adhesion, viability and proliferation onto the external surface of MWCNT/CHI scaffolds with C2C12 cell line (myoblastic mouse cell), which is a multipotent cell line able to differentiate towards different phenotypes under the action of some chemical or biological factors, has been evaluated in vitro and quantified by MTT assays. The evolution of the C2C12 cell line towards an osteoblastic lineage in presence of the recombinant human bone morphogenetic protein-2 (rhBMP-2) has also been studied both in vitro (e.g., following the appearance of alkaline phosphatase activity) and in vivo (e.g., by implantation of MWCNT/CHI scaffolds adsorbed with rhBMP-2 in muscle tissue and evaluation of the ectopic formation of bone tissue).

Comparative analysis of electric, magnetic, and mechanical properties of epoxy matrix composites with different contents of multiple walled carbon nanotubes

AbstractEpoxy composites based on aligned chemical vapor deposition–grown multiwall carbon nanotubes (MWCNTs), containing trapped iron nanoparticles, with weight fractions ranging from 0.03 to 1 wt%, were produced following a well‐known processing way. Electrical and mechanical properties as well as their densities were measured. The results are compared with previous studies investigating the magnetic percolation behavior in the same samples of composites. A percolation threshold at 0.4 wt% of MWCNTs was determined by the electrical property and it agrees with the threshold observed in the magnetic properties. A hop in the porosity and a depression of the bulk mechanical properties were also found at the threshold value. These results point out that there is an efficiency threshold related to the sonication stage of the fabrication process and the weight fraction of MWCNTs, and after this threshold, the initial nanotubes pans were not separated into individual MWCNTs or into small ropes. An optimized sonication stage is proposed and the improvement in the dispersion of the filler is shown. POLYM. COMPOS., 28:612–617, 2007. © 2007 Society of Plastics Engineers

Novel Al-matrix nanocomposites reinforced with multi-walled carbon nanotubes

Novel Al-based nanocomposites reinforced with multi-walled carbon nanotubes were produced by mechanical milling followed by pressure-less sintering at 823 K under vacuum. The interface between Al matrix and the multi-walled carbon nanotubes was examined using transmission electron microscopy. These observation showed that the multi-walled carbon nanotubes were not damaged during the preparation of the nanocomposite and that no reaction products were detected after sintering. The mechanical properties of sintered nanocomposites specimens were evaluated by a compression test. The yield stress ( σ y) and the maximum strength ( σ max) obtained were considerably higher than those reported in the literature for pure Al prepared by the same route. The values for σ y and σ max increase as the volume fraction of multi-walled carbon nanotubes increases. The milling time and the concentration of multi-walled carbon nanotubes have an important effect on the mechanical properties of the nanocomposite.

Thermal transport enhancement of multi-walled carbon nanotubes/ high-density polyethylene composites

Multi-walled carbon nanotubes (MWCNTs) enhanced high-density polyethylene (HDPE) composites were prepared and their thermophysical properties were measured. The thermal diffusivity of the composites increases with the increase in the amount of MWCNTs. A thermal diffusivity of more than three times that of pure HDPE was obtained for 38 vol. % MWCNTs/HDPE composites. An equation based on an effective medium approach model was used to discuss the thermal diffusivity enhancement of MWCNTs/HDPE composites as a function of the volume fraction of MWCNTs. The results from this analysis can be a predictive guideline for further improvements in the thermal transport properties of MWCNTs/HDPE composites. Moreover, the intrinsic longitudinal thermal conductivity kz of an individual MWCNT was deduced from the measured results on the MWCNTs/HDPE composites.

Magnetic properties of multi-walled carbon nanotube–epoxy composites

Epoxy matrix composites have been prepared using as filler different weight fractions (0.03–1 wt%) of CVD grown multi-walled carbon nanotubes (MWCNTs) containing trapped iron nanoparticles. Magnetic characterization performed at room temperature with magnetic field between −19 and 19 kG shows that the nanocomposites are weakly ferromagnetic at room temperature. An abrupt variation in the dependence of both the coercivity field, B C, and remanent magnetization, M R, with the weight fraction of MWCNTs, ϕ, was found for ϕ=0.4%. Results suggest the formation of MWCNTs agglomerates for increasing weight concentrations, in accordance with SEM micrographs.