Umar Khan, Kevin Ryan, Werner J. Blau, Jonathan N. Coleman, The effect of solvent choice on the mechanical properties of carbon nanotube polymer composites, Composites Science and Technology, 67, 15-16, 2007, 3158 - 3167
Composites Science and Technology; 67; 15-16;
Dispersions of single walled nanotubes in N-methyl-2-pyrrolidone have been exposed to
water and variations in storage temperature. The subsequent degradation of dispersion quality
has been monitored using sedimentation, UV-vis-NIR, and AFM measurements. Four
parameters derived from AFM; the root-mean-square bundle diameter, the total number of
dispersed objects (individuals and bundles) per unit volume of dispersion, the number
fraction of individual nanotubes, and the number of individual nanotubes per unit volume of
dispersion were used to quantitatively characterize the dispersion quality as a function of
water content and storage temperature. In addition the positions of the nanotube absorption
peaks were used to track dispersion quality, with redshifts taken as an indication of
aggregation. It was found that water can rapidly shift the dispersion to a new but more
aggregated equilibrium state. In particular the population of individual nanotubes falls to zero
for relatively low amounts of added water. The dispersion quality decreases with increasing
water content, reaching a plateau for all metrics by 20 vol% added water. In addition, it was
also identified that low temperature treatment, i.e. -16, -18, -20, and -22 °C (all above the
freezing point of NMP) does not influence the dispersion quality and stability regardless of
the standing time. However, freezing (-80 °C) or heating (80 °C ) the dispersion leads to a
substantial degradation of the dispersion quality and stability.
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