PVDF/poly(3-methylthiophene)/MWCNT nanocomposites for EMI shielding in the microwave range

This work presents a new approach to enhance EMI shielding efficiency of nanocomposites of dielectric polymers, multiwalled carbon nanotubes (MWCNTs) and intrinsically conducting polymers for account of using core-shell morphology for conducting components. To realize this approach new ternary nanocomposites of poly(vinylidene fluoride) (PVDF), MWCNTs and poly(3-methylthiophene) doped by Cl^- anions (P3MT) were prepared through synthesis of thermally stable core/shell nanocomposites PVDF/P3MT and MWCNT/P3MT. These binary nanocomposites were mixed with pure MWCNTs or PVDF followed by compression molding to prepare the ternary nanocomposites of different morphology to discriminate their EMI shielding properties in a wide frequency range (1-67 GHz). Values of the tangent of dielectric loss angle, the efficiency of transmission, reflection and absorption of microwave radiation, and shielding efficiency (SE) of the specified materials were found from analysis of spectral dependences of their complex dielectric constants. It was shown that while the melt mixing of the binary PVDF/P3MT nanocomposite with MWCNTs both in a pure state and in the binary nanocomposite (MWCNT/P3MT) expectedly strongly enhances SE of the former, this effect is non-linear and depends on presence/absence of the P3MT shell on the MWCNT core. The ternary nanocomposite PVDF/P3MT/MWCNT made of the binary polymer-polymer nanocomposite PVDF/P3MT and pure MWCNTs showed highest SE values at the frequencies above 4.5 GHz up to 68.4 dB at 67 GHz in the case of the 1 mm thickness sample. However, below 4.5 GHz the SE was higher in the case of the ternary nanocomposites containing core/shell MWCNT/P3MT nanocomposite instead of pure MWCNT.