Tailoring MWCNT Dispersion, Blend Morphology and EMI Shielding Properties by Sequential Mixing Strategy in Immiscible PS/PVDF Blends

In this study, we achieved almost 99% (i.e., 19 dB) electromagnetic interference shielding effectiveness (EMI SE), at a much lower cost than poly(vinylidene fluoride) (PVDF)/multi-walled carbon nanotube (MWCNT) nanocomposite, by selectively localizing MWCNT in the polystyrene (PS) phase of PS/PVDF (70:30) blend nanocomposite. This study demonstrates that we can tune MWCNT dispersion, nano localization, electrical conductivity, EMI SE and rheological properties of PS/PVDF/MWCNT nanocomposites by manipulating the mixing order of blend components. Premixing MWCNT with PS phase of PS/PVDF (50:50) blend reduces the agglomeration of MWCNT by 6% (via optical micrograph analysis), compared to the one-step mixing technique. Transmission electron microscope images of PS/PVDF blend nanocomposite show that MWCNT is located in the phase with which MWCNT is premixed. However, for the one-step mixing technique, the MWCNT mostly locates in PVDF with some agglomerates in PS phase. Scanning electron microscope images demonstrate the alteration of blend morphology (e.g., from droplet to co-continuous) depending upon the mixing technique and blend composition. In this context, the PVDF/MWCNT nanocomposite depicts higher EMI SE (19 dB) than PS/MWCNT nanocomposite (12 dB). However, using a specific sequential mixing approach, equal EMI SE to PVDF/MWCNT is achieved in PS/PVDF (70:30) immiscible blend nanocomposite through multiple scattering at significantly low cost. Another key finding is the complex permittivity of hetero-dielectric media demonstrates a linear relation with EMI SE of the blend nanocomposite. Taken together, this study provides a method to design a high-performance microwave absorber by sequential addition of microwave active fillers in the immiscible polymer blends.