Abstract
Metamaterial behavior of polymer nanocomposites (NCs) based on isotactic polypropylene (iPP) and multi-walled carbon nanotubes (MWCNTs) was investigated based on the observation of a negative dielectric constant (ε′). It is demonstrated that as the dielectric constant switches from negative to positive, the plasma frequency (ωp) depends strongly on the ultrasound-assisted fabrication method, as well as on the melt flow index of the iPP. NCs were fabricated using ultrasound-assisted extrusion methods with 10 wt % loadings of MWCNTs in iPPs with different melt flow indices (MFI). AC electrical conductivity (σ(AC)) as a function of frequency was determined to complement the electrical classification of the NCs, which were previously designated as insulating (I), static-dissipative (SD), and conductive (C) materials. It was found that the SD and C materials can also be classified as metamaterials (M). This type of behavior emerges from the negative dielectric constant observed at low frequencies although, at certain frequencies, the dielectric constant becomes positive. Our method of fabrication allows for the preparation of metamaterials with tunable ωp. iPP pure samples show only positive dielectric constants. Electrical conductivity increases in all cases with the addition of MWCNTs with the largest increases observed for samples with the highest MFI. A relationship between MFI and the fabrication method, with respect to electrical properties, is reported.
Highlights
Isotactic polypropylene is a nonpolar polyolefin with high electrical resistivity and used in the fabrication of energy storage materials [1]
The present study showed that methods used for the ultrasound-assist extrusion fabrication influence the electrical properties of isotactic polypropylenes with different melt flow indices (MFI) and of nanocomposites (NCs) with 10 wt % loadings of multi-walled carbon nanotubes using the same polymers
It was demonstrated that the selection of the melt flow index of PP, coupled with an ultrasound-assisted extrusion method, can render metamaterial behavior
Summary
Isotactic polypropylene (iPP) is a nonpolar polyolefin with high electrical resistivity and used in the fabrication of energy storage materials [1]. Metalized biaxially-oriented polypropylene films are widely used in the capacitor. Metalized biaxially-oriented polypropylene films are widely used in the capacitor industry due its high breakdown voltage, its dielectric constant or permittivity (ε′). This behavior changes dramatically when polypropylene is mixed with nanoparticles, This behavior changes dramatically when polypropylene is mixed with nanoparticles, with multi-walled carbon nanotubes (MWCNTs), which usually increase the value of ε′.0. With multi-walled carbon nanotubes (MWCNTs), which usually increase the value of ε. Logakis et al [3] found a value close to 20 for samples when 2 wt % of MWCNT are used. Logakis et al [3] found a value close to 20 for samples containing containing 1.5 wt % of MWCNTs. On the other hand, it has been determined that upon increasing
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