Abstract
The complex ac admittance of a thin film of carbon nanotube/polymer composites depending on both the concentration and the alignment of nanotubes has been studied. The complex ac admittance and the current intensity distribution is numerically calculated using a transfer matrix method, where the discretized mesh model for nanotube/polymer composites is transformed into the network. The percolation threshold increases with the degree of alignment of nanotubes. The vertical dc conductivity parallel to the alignment direction has the maximum at a specific alignment, which is caused by competition between the number of percolating paths and the degree of meandering of the current. Two extreme cases for the dc conductivity are studied; the nanotube-resistance (NT)-limited case and the contact-resistance (CR)-limited case. CR-limited conductivity has much stronger concentration dependence than NT-limited conductivity, since the number of parallel connections of contact-resistors increases more strongly with the nanotube concentration than that of nanotube resistors. The vertical static dielectric constant is enhanced near the percolation threshold and the enhancement is significantly enlarged with the alignment of nanotubes, due to both the decrease in the number of serial connections of minigap capacitors along the path of the imaginary current and the increase in the number of paths.
3 More- Received 1 May 2010
DOI:https://doi.org/10.1103/PhysRevB.82.045204
©2010 American Physical Society