We investigated the draw ratio (DR) dependence of the anisotropic dielectric function and conductivity of styrene butadiene rubbers (SBRs) with different carbon black (CB) concentrations by polarization-sensitive terahertz time-domain spectroscopy. From the frequency dependence of the conductivity in the unstretched SBRs ranging from direct current to terahertz frequencies, it is found that the SBR with a CB concentration above 30 wt. % exhibits percolation conductivity. We investigated the spectral shape of the dielectric function and conductivity of the SBR samples below and above the percolation threshold for two representative DRs in the terahertz frequency region. We found that the DR dependence of the spectral shape is well explained by the effective medium approximation, except for the sample with the CB concentration above 30 wt. % under the unstretched condition. The conductivity in that sample remarkably changes in the low terahertz frequency region, which suggests a change in the CB network by deformation. The investigation of the dielectric anisotropy and percolation conductivity using our polarization technique can be applied to a wide range of elastomer composites.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)