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In the current era of the flourishing development of materials science, polymer nanocomposites have become the focus of research in numerous fields due to their unique and excellent properties. Among them, polyvinylidene fluoride (PVDF)-based nanocomposites have attracted significant attention from researchers because of their great application potential in fields such as electronics and energy storage. Recently, the article "Thermal and electrical properties of PVDF modified Co₃O₄ functionalized MWCNTs" published in RSC Advances delved into the PVDF-modified Co₃O₄-functionalized multi-walled carbon nanotube (MWCNTs) nanocomposites, bringing new ideas for the development of high-performance materials.
Polymer nanocomposites are prepared by adding organic or inorganic nanofillers to polymers, which can significantly enhance the physical properties of polymers. PVDF, a prominent polymer material, is widely used in the piezoelectric and thermoelectric fields and is commonly employed in devices such as capacitors and sensors. However, the poor thermal and electrical properties of pure PVDF limit its further application. To improve these properties, researchers have attempted to add nanofillers, among which 1D nanostructures and carbon nanotubes have received considerable attention. 1D Co₃O₄ performs excellently in fields such as catalysis and battery electrodes, while MWCNTs possess a high specific surface area, good chemical stability, and unique electrical and thermal properties. Combining the two with PVDF is expected to yield nanocomposites with excellent performance.
(1) Experimental Preparation
The experiment selected materials such as powdered PVDF, polyvinylpyrrolidone (PVP), tetrahydrofuran (THF), nitric acid, sulfuric acid, cobalt nitrate hexahydrate, and MWCNTs. The MWCNTs were purified by calcination to remove impurities before use.
1.Preparation of 1D Co₃O₄ Nanostructures: Using an electrospinning machine, cobalt nitrate hexahydrate and PVP were dissolved in THF, stirred evenly, and then electrospun. The nanofibers obtained from electrospinning were collected and calcined to remove PVP, resulting in 1D Co₃O₄ nanostructures.
2.Functionalization of MWCNTs: The MWCNTs were functionalized according to standard protocols to enhance their interaction with PVDF.
3.Preparation of Co₃O₄-MWCNTs/PVDF Nanocomposite Films: Co₃O₄-MWCNTs solutions and PVDF dispersions were prepared separately, mixed, ultrasonicated, and refluxed to promote the integration of the nanostructures with the polymer. Finally, the nanocomposite films were obtained by casting and drying. A total of 10 types of nanocomposite films with different Co₃O₄ and MWCNTs contents were prepared in the experiment.
(2) Characterization Techniques
Multiple techniques, including transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential thermal analysis (TDA), differential scanning calorimetry (DSC), and direct current (DC) conductivity testing, were employed to comprehensively characterize the structure, thermal properties, and electrical properties of the Co₃O₄ nanostructures and PVDF nanocomposite films.
(1) Analysis of Crystal Structure and Phase Transition
As clearly shown in the XDR image in Figure 1, pure PVDF has two absorption bands at 2θ of 20.5° (100) and 39.45° (211), corresponding to the α-phase and γ-phase, respectively. After adding different weight percentages of Co₃O₄-MWCNTs nanostructures, the diffraction patterns of the nanocomposites changed significantly. For example, the XRD pattern of the PC1CNT1 nanocomposite has only one peak at 20.2° (110), showing a slight deviation from the 20.5° (100) peak of pure PVDF. In the PC1CNT1.5 nanocomposite, the main peak of pure PVDF at 2θ of 20.5° decreased significantly, and new peaks at 7.60° and 16.45° appeared. The appearance of these new peaks and the changes in the intensity of the original peaks clearly indicate that after adding the nanofillers, PVDF underwent a transformation from the non - polar α-phase to the polar β-phase, thus confirming the crystal structure changes and phase transition of the nanocomposites.
Figure 1. XRD patterns of PVDF and its nanocomposites with Co₃O₄ nanowires and multi - wall carbon nanotubes (MWCNTs).
(2) Analysis of PVDF Phase State
FTIR analysis further revealed the phase state of PVDF. As shown in Figure 2, pure PVDF has different absorption bands at 479 cm⁻¹, 515 cm⁻¹, 600 cm⁻¹, 840 cm⁻¹, 876 cm⁻¹, 1166 cm⁻¹, and 1400 cm⁻¹. When loaded with Co₃O₄-MWCNTs nanostructures, the peaks of the non - polar α-phase and the weakly polar γ-phase weakened or disappeared, and new peaks corresponding to the β-phase appeared at 563 cm⁻¹, 660 cm⁻¹, and 1275 cm⁻¹. Moreover, the intensity of the β-phase peaks increased with the increase in the nanofiller concentration. This result not only verified the existence of the α-phase and β-phase in PVDF but also corroborated the XRD results, indicating that the addition of nanofillers promoted the formation of the β-phase and further demonstrated the phase state changes of the nanocomposites.
Figure 2. FTIR curves of blank PVDF and PVDF nanocomposites with different wt% of Co₃O₄ and functionalized MWCNTs nanostructures.
(3) Analysis of Thermal Performance Improvement
The results of TGA, TDA, and DSC tests fully demonstrated the significant improvement in the thermal stability of the nanocomposites. As shown in Figure 3, pure PVDF began to degrade after 340 °C, with a total weight loss of 66%. After adding Co₃O₄-MWCNTs, the initial degradation temperature (Tonset) and the end degradation temperature (Tend) of the nanocomposites were significantly higher than those of pure PVDF and increased with the increase in the nanofiller concentration. For example, the Tonset of PC1CNT1 increased to 401 °C, and the Tonset of PC5CNT3 reached 452 °C. This is due to the strong interaction between the nanofillers and the PVDF chains, which restricts the degradation of PVDF.
Figure 3. TGA patterns of pure PVDF against its nanocomposite films loaded with different wt% of Co₃O₄ and functionalized MWCNTs nanostructures. (a) PVDF, PC1CNT1, PC1CNT1.5, PC1CNT3 (b) PVDF, PC3CNT1, PC3CNT1.5, PC3CNT3 (c) PVDF, PC5CNT1, PC5CNT1.5, and PC5CNT3.
It can also be seen from Figure 4 that the peak temperature (Tp) of the nanocomposite films increased with the increase in the filler concentration, further indicating the improvement in the thermal stability of the nanocomposites. DSC analysis also showed that after adding Co₃O₄-MWCNTs, the melting point (Tm) of the PVDF nanocomposites increased slightly, which reflects the influence of the nanofillers on the phase transition of PVDF and shows the potential of the nanocomposites in high - temperature applications.
Figure 4. TDA patterns of pure PVDF against its nanocomposite films loaded with different wt% of Co₃O₄ and functionalized MWCNTs nanostructures. (a) PVDF, PC1CNT1, PC1CNT1.5, PC1CNT3 (b) PVDF, PC3CNT1, PC3CNT1.5, PC3CNT3 (c) PVDF, PC5CNT1, PC5CNT1.5, and PC5CNT3.
(4) Analysis of Dielectric and Conductive Properties
The study found that when the Co₃O₄ content was 0.5 wt% and the MWCNTs content was 0.3 wt%, the dielectric properties of the nanocomposites were significantly improved. In terms of conductivity, the conductivity of the nanocomposites increased with the increase in the nanofiller content. As shown in the DC conductivity test results in Figure 5, the DC conductivity of pure PVDF was very low. After adding Co₃O₄-MWCNTs, the DC conductivity of the nanocomposites increased significantly. In samples with high filler content, Co₃O₄ and MWCNTs formed a conductive network, which promoted electron migration and improved the conductivity. In samples with low filler content, the distance between the conductive fillers was large, making it difficult to form a continuous conductive path, resulting in low conductivity. This is fully attributed to the strong interaction between the PVDF polymer and the nanofillers, which facilitates charge transfer and thus improves the conductivity.
Figure 5. DC conductance (a) and dielectric loss (b) of blank PVDF and its nanocomposites loaded with different wt% of Co₃O₄ and functionalized MWCNTs nanostructures.
This study successfully prepared Co₃O₄-MWCNTs/PVDF nanocomposites using electrospinning machine and comprehensively characterized the structure and properties of the materials using multiple techniques such as XRD, FTIR, TGA, TDA, DSC, and conductivity testing. The results showed that the nanocomposites achieved the transformation of PVDF from the non - polar α-phase to the polar β-phase, significantly improving the thermal stability, dielectric properties, and conductivity. This provides important insights for the development of advanced nanocomposites with excellent thermal and electrical properties, and these materials have broad application prospects in fields such as electronics and energy storage devices.
Article Source: https://doi.org/10.1039/D4RA07239A
