Destruction and formation of a carbon nanotube network in polymer melts: Rheology and conductivity spectroscopy

Destruction and formation of the carbon nanotube network in polymer melts have been investigated by a combination of conductivity spectroscopy and dynamic-mechanical analysis for polycarbonate (PC) containing multiwalled carbon nanotubes. The combined setup allows simultaneous time-resolved measurements of electrical conductivity, dielectric permittivity and dynamic shear modulus. Furthermore, well-defined shear deformations can be applied to the samples. After annealing the samples well above glass transition short shear deformations were applied to the melt. These deformations lead to a decrease of the conductivity by about 6 orders of magnitude and of the real part of the shear modulus (G′) by a factor of 20. In the rest time after the shear deformation a complete recovery of the conductivity and G′ modulus was observed. The changes in conductivity and G′ were assigned to destruction and reformation of agglomerates, which are assumed to be conductive spherical objects containing loosely packed nanotubes. For a quantitative description of the time dependent electrical conductivity a simple model combining cluster aggregation and electrical percolation is applied.