Relationship Between Dispersion Metric and Properties of PMMA/SWNT Nanocomposites.
Relationship Between Dispersion Metric and Properties of
PMMA/SWNT Nanocomposites.
(1504 K)
Kashiwagi, T.; Fagan, J.; Douglas, J. R.; Yamamoto, K.;
Heckert, A. N.; Leigh, S. D.; Obrzut, J.; Du, F.;
Lin-Gibson, S.; Mu, M.; Winey, K. I.; Haggenmueller, R.
Polymer, Vol. 48, No. 16, 4855-4866, July 2007.
Keywords:
nanocomposites; dispersion; polymethyl methacrylate;
composite materials; equations; thermal stability;
electrical resistivity; flammability; mass loss;
physical properties
Abstract:
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-walled carbon nanotubes (SWNTs)
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 property of the
nanocomposites correlate well with the RDI. For the
nanocomposites 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.
