Synthesis and investigation of the electrical and dielectric properties of Co3O4/(CMC+PVA) nanocomposite films

Tuning the band gap, optical, mechanical, and electrical features of a bio-blend by Cr2O3/V2O5 nanofillers for optoelectronics and energy applications

This work presents a facile approach for controlling the optical and electrical parameters of a biopolymeric matrix for optoelectronics. Vanadium oxide (V2O5) and chromium oxide (Cr2O3) nanoparticles (NPs) were prepared and incorporated into the carboxymethylcellulose/polyethylene glycol (CMC/PEG) blend by simple chemical techniques. Transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD) data showed that V2O5 and Cr2O3 exhibited spherical shapes with sizes in the range of 40-50 nm and 10-20 nm, respectively. In addition, the blend's degree of crystallinity was sensitive to the V2O5 and Cr2O3 doping ratios. The scanning electron microscopy (FE-SEM) and the elemental chemical analysis (EDAX) used to study the filler distribution inside the blend, and confirmed the existence of both V and Cr in the matrix. Fourier transform infrared (FTIR) spectroscopy showed that the dopants significantly affected the blend reactive (C-O-C, OH, and C=O) groups. The stress-strain curves illustrated the reinforcing effect of the dopants up to 1.0 wt\% Cr2O3/V. The transmittance and absorption index spectra in the visible-IR wavelengths decreased with increasing filler content. Utilizing Tauc's relation and (optical) dielectric loss, the direct (indirect) band gap narrowed from 5.6 (4.5) eV to 4.7 (3.05) eV at 1.0   wt\% Cr2O3/V. All films have an index of refraction in the range of 1.93-2.17. AC conductivity was improved with increasing filler content and temperature. The energy density at 50 °C is in the range of 1-3 J/m3. The influence of V2O5 and Cr2O3 content on the optical conductivity, dielectric constant, loss, and dielectric modulus of CMC/PEG was reported. These enhancements in electrical and optical properties, along with the potential for band gap engineering, offer promising prospects for advanced applications in optoelectronics and energy-related fields.

Enhancement of physico-chemical, optical, dielectric and antimicrobial properties of polyvinyl alcohol/carboxymethyl cellulose blend films by addition of silver doped hydroxyapatite nanoparticles

Hydroxyapatite nanoparticles doped with silver AgHA-NPs were synthesized successfully then added with various mass fractions to a mixed solution of polyvinyl alcohol (PVA)/ carboxymethyl cellulose (CMC) using the casting technique. Experimentally, the influence of silver doped hydroxyapatite nanoparticles on the structural, optical, dielectric and antimicrobial properties of nanocomposite films was investigated. X-ray diffraction and Fourier transformation infrared spectroscopy were used to explore the structural features of these films. The XRD analysis revealed the amorphous nature of PVA/CMC blend and the intensity of the characteristic peak of the virgin polymers in the nanocomposite spectrum being much reduced as the doping level was increased. The FT-IR spectra indicated that the blend components were miscible by revealing the functional groups of two polymers that interacted through the formation of a hydrogen bond while, the FT-IR spectra of nanocomposite confirmed the good interaction between the blend chains and AgHA-NPs. The morphological graphs of the prepared blend were formed as hexagonal grains with size distribution around 18.36–24.11 μm. The addition of AgHA-NPs changed the surface morphology of the blend significantly. The optical properties of PVA/ CMC blend and nanocomposites films were measured in the 200–800 nm wavelength range. Optical measurements showed that the optical transmittance for pure blend was nearly 90% while it decreased to 50% with increasing AgHA-NPs contents up to 40 wt.%. The energy gap values calculated by Tauc's model and those determined by ASF model are consistent, where their values reduced by AgHA-NPs incorporation. The dielectric constant of all samples were studied in range of temperatures (303–405 K) and from100 kHz to 1.0 MHz, range of frequencies. The Correlated Barrier Hopping (CBH) is the most appropriate conduction mechanism based on the frequency dependence of the ac conductivity. Silver ion release was examined showed that he film loaded with 10 wt.% AgHA-NPs has a small release of silver ion, while the amount of the Ag+ released from the samples increased slowly with increasing the content of AgHA-NPs. PVA/CMC/AgHA films were tested for antibacterial activity against both (Bacillus subtilis) and (Escherichia coli) as well as the anti-fungal activity against (Candida albicans),their results showing an increase in the activity index as the filling level of AgHA-NPs increases. The study confirmed that doping of AgHA-NPs into PVA/CMC improves both electrical conductivity and antimicrobial efficiency and these nanocomposites might be recommended for further work in biomedical applications such as wound dressing and infection control.

High dielectric thin films based on barium titanate and cellulose nanofibrils

A series of composite films based on tetragonal barium titanate (BTO) and cellulose nanofibrils (CNF) with high dielectric constant are prepared using a casting method in aqueous solution. No organic solvent is involved during the preparation, which demonstrates the environmental friendliness of the novel material. With less than 30 wt% of filler loading, the excellent distribution of BTO nanoparticles within the CNF matrix is revealed by the FE-SEM images. The dielectric constant of the CNF/BTO (30 wt%) composite film reaches up to 188.03, which is about seven times higher than that of pure CNF (25.24), while the loss tangent only rises slightly from 0.70 to 1.21 (at 1 kHz). The thin films kept their dielectric properties on an acceptable level after repeatedly twisting or rolling 10 times. The improvement of thermal stability is observed with the presence of BTO. The outstanding dielectric properties of the CNF/BTO composite film indicates its great potential to be utilized in energy storage applications.

The high dielectric thin films based on cellulose fibrils and tetragonal barium titanate exhibit excellent dielectric properties, flexibility and durability.

Frequency and temperature-dependent impedance spectroscopy of PVA/PEG polymer blend film

In this work, polymer blend films based on polyvinyl alcohol (PVA)/poly(ethylene glycol) (PEG) were prepared by solution casting technique. X-ray diffraction (XRD) analysis was performed to investigate the structural details of the polymer blend. XRD pattern confirms the polycrystalline nature of the films. Sandwich structures of the type Ag-PVA/PEG-Ag were formed to study the dielectric and conduction properties in the frequency range 300 Hz–3 MHz and at different temperatures varying from 298 K to 420 K. Experimental results show that both dielectric constant ( ε′) and dielectric loss ( ε″) values were strong functions of frequency and temperature. The AC conductivity ( σAC) was found to obey the power law Aωs and correlated barrier hopping as the conduction mechanism. The imaginary part of electric modulus shows peak shifting corresponding to relaxation mechanisms. Electric modulus study was also found to support the dielectric permittivity data.