Comparative Analysis of Dielectric and Optoelectronic Properties in Multifunctional Nanocomposites

Polymer Chemistry Nanoscience Electrical Engineering Chemistry Materials Science Engineering Optics Materials Chemistry Physics
nanocomposite PVDF α-phase β-phase optical properties dielectric properties

Research Background

In recent years, multiferroic nanocomposites have garnered significant attention due to their wide-ranging applications in sensors, energy storage systems, transducers, and actuators. These materials combine the advantages of polymers and ceramic matrices, such as being lightweight, easy to process, corrosion-resistant, having high mechanical strength, as well as exhibiting piezoelectric and magnetoelectric behavior. Polyvinylidene fluoride (PVDF), as an important polymer, has become an ideal choice for preparing multiferroic nanocomposites due to its excellent dielectric constant, low reactivity, high thermoplasticity, flexibility, and transparency.

However, PVDF has multiple crystalline phases (α, β, γ, and δ), where the α-phase is non-polar, while the β-phase exhibits significant piezoelectric, ferroelectric, and pyroelectric properties due to the highly ordered arrangement of negative fluorine atoms and positive hydrogen ions on either side of the polymer chain. Therefore, optimizing the concentration of the β-phase in PVDF is crucial for enhancing its performance. Additionally, magnetic nanoparticles (such as nickel ferrite and manganese ferrite) have attracted widespread attention due to their unique magnetic and dielectric properties. Introducing these magnetic nanoparticles into the PVDF matrix can not only enhance the optical and dielectric properties of the material but may also impart new functional characteristics.

This study aims to improve the optical, dielectric, and electrical properties of PVDF nanocomposites by incorporating Ni₀.₂Mn₀.₈Fe₂O₄ ferrite nanoparticles and explore their potential application value.

Source of the Paper

This paper was written by Sarah A. Alshehri et al., with authors from Princess Nourah Bint Abdulrahman University in Saudi Arabia, Sinai University, and Tanta University in Egypt. The paper was accepted on December 25, 2024, and published in the journal Optical and Quantum Electronics, Volume 57, Article Number 159. The DOI is 10.1007/s11082-024-08017-8.

Research Process and Methods

a) Research Process and Experimental Design

This study is mainly divided into the following steps:

1. Sample Preparation

The research team used the solution casting method to prepare PVDF/Ni₀.₂Mn₀.₈Fe₂O₄ nanocomposite films. The specific steps are as follows: - Dissolve 1.5 g of PVDF in 25 mL of dimethylformamide (DMF) at 50°C with continuous stirring to ensure complete dissolution. - Add Ni₀.₂Mn₀.₈Fe₂O₄ nanoparticles according to different weight ratios (x = 0, 0.2, 0.4, 0.6, 0.8 g) and continue stirring for 90 minutes to achieve uniform dispersion. - Pour the mixture into clean glass petri dishes and dry it in an oven at 50°C for 24 hours to evaporate the solvent and form the film.

2. Sample Characterization

To comprehensively evaluate the structural, optical, and dielectric properties of the nanocomposites, the research team employed the following characterization techniques: - X-ray Diffraction (XRD): Used to analyze the crystal structure and grain size of the samples. - Scanning Electron Microscopy (SEM): To observe the surface morphology and particle distribution of the samples. - Fourier Transform Infrared Spectroscopy (FTIR): To identify different crystalline phases of PVDF (α, β, and γ). - UV-Visible Spectrophotometry: To measure the optical absorption coefficient and bandgap energy. - Broadband Dielectric Spectroscopy (BDS): To measure dielectric constant, AC conductivity, and impedance over a frequency range of 10 Hz to 10 MHz.

3. Data Analysis

The research team used various algorithms and formulas to analyze the data, including: - Debye-Scherrer formula: To calculate grain size. - Williamson-Hall analysis: To distinguish grain size and microstrain. - Tauc plot: To determine indirect bandgap energy. - Urbach energy analysis: To assess the degree of internal disorder in the material.

b) Main Results

1. Structural Analysis

  • XRD analysis showed that as the content of Ni₀.₂Mn₀.₈Fe₂O₄ increased, the crystallinity of PVDF decreased, and the amorphous phase increased. The intensity of the α-phase gradually weakened, while the intensity of the β-phase remained relatively stable.
  • SEM images indicated that Ni₀.₂Mn₀.₈Fe₂O₄ nanoparticles were uniformly distributed in the PVDF matrix, but as the doping amount increased, particle aggregation became more pronounced.
  • FTIR spectra further confirmed the transition from the α-phase to the β-phase, which might be due to the interaction between magnetic nanoparticles and PVDF chains.

2. Optical Properties

  • Optical absorption spectra showed that as the content of Ni₀.₂Mn₀.₈Fe₂O₄ increased, the absorption coefficient (α) significantly improved, and the absorption edge exhibited a redshift.
  • Bandgap energy decreased from 5.59 eV for pure PVDF to 4.90 eV after doping, indicating enhanced conductivity of the material.
  • Refractive index (n) increased with the increase in Ni₀.₂Mn₀.₈Fe₂O₄ content, ranging from 1.92 to 2.02.

3. Dielectric Properties

  • In the low-frequency range, the dielectric constant (ε’) decreased with increasing frequency but stabilized in the high-frequency range.
  • As the content of Ni₀.₂Mn₀.₈Fe₂O₄ increased, the maximum value of ε’ reached 15 (at x = 0.6), which might be attributed to the enhancement of interfacial polarization effects.
  • AC conductivity (σ’) was independent of frequency in the low-frequency range but followed Jonscher’s universal power law in the high-frequency range.

c) Research Conclusions

This study shows that incorporating Ni₀.₂Mn₀.₈Fe₂O₄ nanoparticles into the PVDF matrix can significantly improve the optical and dielectric properties of nanocomposites. Specifically: - The increase in the β-phase enhanced the piezoelectric and ferroelectric properties of the material. - The reduction in bandgap energy and the increase in refractive index enhanced the optical response of the material. - Improvements in dielectric constant and AC conductivity make it potentially valuable for sensors and energy storage devices.

d) Research Highlights

  1. Innovative Method: This is the first systematic study of the impact of Ni₀.₂Mn₀.₈Fe₂O₄ on the properties of PVDF nanocomposites.
  2. Important Findings: Revealed how magnetic nanoparticles promote the transition from the α-phase to the β-phase in PVDF.
  3. Potential for Multi-field Applications: The material has broad application prospects in flexible electronic devices, sensors, and energy storage systems.

Research Significance and Value

This study not only deepens the understanding of PVDF/ferrite nanocomposites but also provides new ideas for developing high-performance multifunctional materials. By optimizing the doping ratio of nanoparticles, the optical and dielectric properties of the material can be further tuned to meet the needs of specific application scenarios. Additionally, the methods and conclusions of this study provide important references for the design and development of other similar materials.