Single-walled carbon nanotube (SWNT)/poly(methyl methacrylate) (PMMA) nanocomposites
were prepared via our coagulation method providing uniform dispersion of the nanotubes in the polymer
matrix. Optical microscopy, Raman imaging, and SEM were employed to determine the dispersion of
nanotube at different length scales. The linear viscoelastic behavior and electrical conductivity of these
nanocomposites were investigated. At low frequencies, G‘ becomes almost independent of the frequency
as nanotube loading increases, suggesting an onset of solidlike behavior in these nanocomposites. By
plotting G‘ vs nanotube loading and fitting with a power law function, the rheological threshold of these
nanocomposites is ∼0.12 wt %. This rheological threshold is smaller than the percolation threshold of
electrical conductivity, ∼0.39 wt %. This difference in the percolation threshold is understood in terms of
the smaller nanotube−nanotube distance required for electrical conductivity as compared to that required
to impede polymer mobility. Furthermore, decreased SWNT alignment, improved SWNT dispersion, and/or longer polymer chains increase the elastic response of the nanocomposite, as is consistent with our
description of the nanotube network.
Particle spatial dispersion is a crucial characteristic of polymer composite materials and this property is recognized as especially important in nanocomposite materials due to the general tendency of nanoparticles to aggregate under processing conditions. We introduce dispersion metrics along with a specified dispersion scale over which material homogeneity is measured and consider how the dispersion metrics correlate quantitatively with the variation of basic nanocomposite properties. We then address the general problem of quantifying nanoparticle spatial dispersion in model nanocomposites of single wall carbon nanotubes (SWNT) dispersed in poly(methyl methacrylate) (PMMA) at a fixed SWNT concentration of 0.5 % using a 'coagulation' fabrication method. Two methods are utilized to measure dispersion, UV-Vis spectroscopy and optical confocal microscopy. Quantitative spatial dispersion levels were obtained through image analysis to obtain a 'relative dispersion index' (RDI) representing the uniformity of the dispersion of SWNTs in the samples and through absorbance. We find that the storage modulus, electrical conductivity, and flammability containing the same amount of SWNTs, the relationships between the quantified dispersion levels and physical properties show about four orders of magnitude variation in storage modulus, almost eight orders of magnitude variation in electric conductivity, and about 70 % reduction in peak mass loss rate at the highest dispersion level used in this study. The observation of such a profound effect of SWNT dispersion indicates the need for objective dispersion metrics for correlating and understanding how the properties of nanocomposites are determined by the concentration, shape and size of the nanotubes. conditions. We introduce dispersion metrics along with a specified dispersion scale over which material homogeneity is measured and consider how the dispersion metrics correlate quantitatively with the variation of basic nanocomposite properties. We then address the general problem of quantifying nanoparticle spatial dispersion in model nanocomposites of single wall carbon nanotubes (SWNT) dispersed in poly(methyl methacrylate) (PMMA) at a fixed SWNT concentration of 0.5 % using a 'coagulation' fabrication method. Two methods are utilized to measure dispersion, UV-Vis spectroscopy and optical confocal microscopy. Quantitative spatial dispersion levels were obtained through image analysis to obtain a 'relative dispersion index ' (RDI) representing the uniformity of the dispersion of SWNTs in the samples and through absorbance. We find that the storage modulus, electrical conductivity, and flammability † This was carried out by the National Institute of Standards and Technology (NIST), an agency of the US Government and is not subject to copyright in the US. ‡ Correspondence to: T. Kashiwagi (E-mail: takashi.kashiwagi@nist.gov) 1 property of the nanocomposites correlates well with the RDI. For the nanocomposites containing the same amount of SWNTs, the relationships betw...
A new method for preparing SWNT/epoxy nanocomposites has been developed which involves high shear mixing of the epoxy resin and SWNT and heat treating the mixture prior to introducing the hardener. The glass transition temperature of the epoxy resin is unaffected by the presence of nanotubes. An improvement of 17% in flexural modulus and 10% in flexural strength has been achieved at 0.05 wt% of nanotubes. These improvements in flexural modulus and strength are attributed to good dispersion of the nanotubes and grafting of epoxy resin to SWNT by an esterification reaction.
AbstractA new method for preparing SWNT/epoxy nanocomposites has been developed which involves high shear mixing of the epoxy resin and SWNT and heat treating the mixture prior to introducing the hardener. The glass transition temperature of the epoxy resin is unaffected by the presence of nanotubes. An improvement of 17% in flexural modulus and 10% in flexural strength has been achieved at 0.05 wt% of nanotubes. These improvements in flexural modulus and strength are attributed to good dispersion of the nanotubes and grafting of epoxy resin to SWNT by an esterification reaction.
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