Investigation of electromagnetic characteristics of polyaniline composites

With the increase of electromagnetic pollution and the wide use of commercial and military products, there is an increasing interest in electromagnetic interference (EMI) shielding. This article mainly aims at the effect of high magnetic field (HMF) on the grain shape and electrical conductivity of HCI-doped polyaniline (Pani-HCl), and the electrical conductivity and EMI shielding effectiveness (SE) of the conducting composites made from silicone rubber (SR) with different loading levels of Pani-HCl (without HMF) in the low frequency range from 3 to 1500 MHz. The result indicates that SE of the composites containing Pani-HCl (without HMF) increases and the volume resistivity decreases with increasing mass ratio loading of Pani-HCl in the SR. The measured SE of the composites are from 16 to 19.3 dB at 100 mass ratio loading of Pani-HCl and the volume resistivity decreases nine orders of magnitude compared with that of the emeraldine base form of Pani (Pani-EB) composites. The influence of HMF on electrical conductivity and grain shape of Pani-HCl is great. The grain shape of the in situ polymerization of PAN in 10T is an open-ramified rod-like pattern with a diameter of 50 nm and that of secondary doped PAN in 10T change to spherical structures of diameter of about 20-30nm, which are obviously different from the irregular reef-like particle shape of doped PAN in 0T. It is thought that the reason for the different grain shape is anisotropic diamagnetic susceptibility of doped PAN and orientations of the HMF.