Chiral polyaniline with superhelical structures for enhancement in microwave absorption

Chiral polyaniline (PANI) with superhelical structure is successfully synthesized via in situ polymerization using chiral acid as dopant and self-assembly technique. The morphology and structure were characterized by scanning electron microcopy, transmission electron microscopy, fourier transform infrared spectra, circular dichroism, X-ray diffractometer and X-ray photoelectron spectra, which demonstrate polyaniline has chirality and superhelical structure. A possible formation process of the superhelical structure was also discussed. The microwave absorption properties of superhelical chiral PANI was investigated in the frequency range of 2-18 GHz. The results indicated that the superhelical chiral PANI exhibit substantially enhanced electromagnetic losses compared to conventional PANI. The minimum reflection loss (RL) of the superhelical chiral PANI can reach - 31.7 dB at 11.7 GHz, and the bandwidth less than -10 dB is 3.8 GHz with absorber thickness of 1.7 mm. The enhanced microwave absorbing property can be attributed to multi-loss mechanisms, good impedance matching and the cross-polarization effects resulting from the superhelical structure and chirality.