Аннотация:This chapter presents the results of the investigation of
microstructure, electrical conductivity of nanocarbon-polymer
composites, and the parameters of interaction with microwave
electromagnetic radiation (EMR). It was found that the type of formed
conducting cluster depends on the morphology of carbonfiller particles.
The chain structure of disk-like graphite nanoplatelets (GNPs) in polymer
matrix is formed while in case of entangled cylindrical carbon nanotubes
(CNTs) the composite structure with interpenetrating filler components is
formed.
Three-dimensional (3-D) Monte Carlo simulation has been
performed to predict the percolation threshold for the electrical
conductivity of polymer composites filled with conductive particles of
various morphologies. It was found that percolation threshold decreases
with the increase of the aspect ratio of nanocarbon particles, and cylindrical particles are more preferred for decreasing the percolation
threshold as compared with disk-like particles with the same aspect ratio.
The model of the effective electrical conductivity has been developed
for carbon-polymer composites. This model takes into account the
morphology of the carbon filler, its intrinsic electrical conductivity, the
spatial orientation of the anisometric carbon particles in the composite
and the electrical contact resistance between particles in the formed
continuous filler chains. The model enables the determination of the
electric transport character in the composite and shows that the anisotropy
of the effective electrical conductivity depends on the conductivity
anisotropy of individual carbon particles as well as on their orientation in
the polymer matrix.
We have examined the epoxy composites with hybrid fillers: mixture
of two conductive fillers with different geometry (graphite nanoplatelets
GNPs and cylindrical cut carbon fibers CFs or carbon nanotubes CNTs)
or mixture of carbon nanofiller and disperse dielectric filler (boron
nitride, barium hexaferrite). Our study has shown the impact of hybrid
fillers in CMs on the percolation threshold and the value of electrical
conductivity as well as on its anisotropy at high filler content.
The electrical conductivity, complex permittivity, EMR reflection,
transmission, and absorption indexes have been determined in the
microwave range of 25.8-37.5 GHz for epoxy composites with
nanocarbon fillers. The empirical relationship between EMR shielding
efficiency SET and electrical conductivity σdc of CMs was determined.
It was demonstrated that the EMR reflection and absorption indexes for
carbon-epoxy composites can be satisfactorily described within the
classic shielding theory for continuous medium by using the effective
parameters of electrical conductivity and permittivity of composites. This
allows developing the composite materials with predicted shielding
characteristics.
Keywords: nanocarbon fillers, nanocomposite, electrical conductivity,
permittivity, electromagnetic shielding.