Enhanced dielectric properties of PVDF polymer nanocomposites: A study on gold-decorated, surface-modified multiwalled carbon nanotubes

The integration of surface-modified multiwalled carbon nanotubes (fMWCNTs) into polymer nanocomposites has been extensively studied for their potential to enhance dielectric properties. This study, however, pioneers the use of a novel hybrid filler comprising fMWCNTs coated with metal nanoparticles, specifically aimed at augmenting the dielectric performance of polymers. In our research, poly(vinylidene fluoride) (PVDF) nanocomposite films were synthesized using fMWCNTs with a diameter of ∼6-9 nm and a length of 5 μm, adorned with gold nanoparticles (nAu) of ∼5.4 ± 0.9 nm via an adapted Turkevich method. Comprehensive analyses were conducted on nAu-fMWCNTs hybrid powder and their nanocomposites in PVDF with varying filler concentrations, confirming the formation of nAu-fMWCNTs with a weight ratio of 1.1 : 98.9. Three-phase percolative nanocomposites were produced by dispersing the hybrid filler in N,N-dimethylformamide, facilitated by interactions between the negative charge of nAu-fMWCNTs (zeta potential of ∼ -40.43 ± 0.46 mV) and polar phases of PVDF. This was verified through zeta potential and Fourier-transform infrared spectroscopy analyses. The dielectric permittivity (ε') of the nanocomposites significantly increased from 17.8 to 524.8 (at 1 kHz) with filler loadings from 0.005 to 0.01 vol%, while the dielectric loss tangent (tanδ) showed a minor increase from 0.05 to 1.18. These enhancements are attributed to the elevated permittivity of nAu-fMWCNTs hybrid powder, PVDF's transition to the β-phase, and interfacial polarization effects. The restrained growth of nAu on fMWCNTs and the inhibition of conductive pathways in the polymer matrix contributed to the low tanδ values.

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.