Microwave absorption properties of polyaniline/poly(vinyl alcohol)/multi-walled carbon nanotube composites in thin film and nanofiber layer structures

Electrospinning of conductive polymer blends offers high potential to prepare novel materials for electronical applications. The main aim of this work is to fabricate poly(vinyl alcohol) (PVA), polyaniline (PANI), and multi walled carbon nanotubes (MWNT) composites in thin film and nanofiber layer structures and then compare their microwave absorption behavior. First, optimum ratios for blending PVA, PANI, Camphorsulfonic acid (CSA) and MWNT were obtained. Then under optimized ratios, composite solutions of PVA: PANI-CSA, and PVA/PANI-CSA/MWNT were fabricated to nanofiber layer and thin film structures. Based on scanning electron microscope (SEM) micrographs, the PVA/PANI-CSA nanofiber samples at low content of PANI-CSA presented a very uniform surface and without any beads but some beads started to develop at higher PANI-CSA content. However, the SEM analysis of the PVA/PANI-CSA/MWNT films revealed the uniform appearance for all composites. But, some aggregation and local irregularities on the surface were observed due to the presence of MWNT in the composite structure. Microwave absorption behavior was evaluated using vector network analyzers in the frequency range of 8-12 GHz (X-band) for all samples. It was observed that absorption microwave properties of PVA/PANI-CSA nanofibers improved with increasing in the loading levels of PANI-CSA in the mixture. Microwave absorption properties of the PVA/PANI-CSA/MWNT composite nanofiber absorbers have been compared with thin films at various thicknesses by measuring the relative maximum reflection loss (dB/mm) of samples. The PVA/PANI-CSA/MWNT composite nanofibers with the layer thickness of 0.1 mm presented two remarkable absorbing peaks versus one absorbing peak in nanocomposite films with similar thickness. The relative maximum reflection loss in PVA/PANI-CSA/MWNT composite nanofiber has reached -230 dB/mm at frequency of 8.6 GHz which is nearly 8 times higher than -28 dB/mm at frequency of 8.4 GHz for PVA/PANI-CSA/MWNT film samples.