Electrical and thermal phenomena in low-density polyethylene/carbon black composites near the percolation threshold

Advances in Monte Carlo Method for Simulating the Electrical Percolation Behavior of Conductive Polymer Composites with a Carbon-Based Filling

Conductive polymer composites (CPCs) filled with carbon-based materials are widely used in the fields of antistatic, electromagnetic interference shielding, and wearable electronic devices. The conductivity of CPCs with a carbon-based filling is reflected by their electrical percolation behavior and is the focus of research in this field. Compared to experimental methods, Monte Carlo simulations can predict the conductivity and analyze the factors affecting the conductivity from a microscopic perspective, which greatly reduces the number of experiments and provides a basis for structural design of conductive polymers. This review focuses on Monte Carlo models of CPCs with a carbon-based filling. First, the theoretical basis of the model's construction is introduced, and a Monte Carlo simulation of the electrical percolation behaviors of spherical-, rod-, disk-, and hybridfilled polymers and the analysis of the factors influencing the electrical percolation behavior from a microscopic point of view are summarized. In addition, the paper summarizes the progress of polymer piezoresistive models and polymer foaming structure models that are more relevant to practical applications; finally, we discuss the shortcomings and future research trends of existing Monte Carlo models of CPCs with carbon-based fillings.

Fabrication of novel strain sensors from green TPV nanocomposites based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/silicone rubber/silicon-modified graphene oxide

In this study, a new thermoplastic vulcanizate (TPV) blend of silicone rubber (SR) and poly (3-hydroxybutyrate-co-3-hydroxy valerate) (PHBV) including silicon-modified graphene oxide (SMGO), is used to fabricate highly flexible and sensitive strain sensors. The sensors are built with an extremely low percolation threshold of 1.3 vol%. We investigated the effect of adding SMGO nanoparticles to strain-sensing applications. The findings demonstrated that increasing the SMGO concentration enhanced the composite's mechanical, rheological, morphological, dynamic mechanical, electrical, and strain-sensing capabilities. But too many SMGO particles can reduce elasticity and cause nanoparticle aggregation. The nanocomposite's gauge factor (GF) values were discovered to be 375, 163, and 38, with nanofiller contents of 5.0 wt%, 3.0 wt%, and 1.0 wt% respectively. Cyclic strain-sensing behavior showed their ability to recognize and classify various motions. Due to its superior strain-sensing capabilities, TPV5 was chosen to assess the repeatability and stability of this material when utilized as a strain sensor. The sensor's excellent stretchability, sensitivity (GF = 375), and remarkable repeatability during cyclic tensile testing allowed them to be stretched beyond 100% of the applied strain. This study offers a new and valuable method for building conductive networks in polymer composites, with potential uses in strain sensing, especially in biomedical applications. The study also emphasizes the potential of SMGO as a conductive filler for developing extremely sensitive and flexible TPEs with enhanced, environmentally friendly features.

Thermoelectric Properties of N-Type Poly (Ether Ether Ketone)/Carbon Nanofiber Melt-Processed Composites

The thermoelectric properties, at temperatures from 30 °C to 100 °C, of melt-processed poly(ether ether ketone) (PEEK) composites prepared with 10 wt.% of carbon nanofibers (CNFs) are discussed in this work. At 30 °C, the PEEK/CNF composites show an electrical conductivity (σ) of ~27 S m^-1 and a Seebeck coefficient (S) of -3.4 μV K^-1, which means that their majority charge carriers are electrons. The origin of this negative Seebeck is deduced because of the impurities present in the as-received CNFs, which may cause sharply varying and localized states at approximately 0.086 eV above the Fermi energy level (E_F) of CNFs. Moreover, the lower S, in absolute value, found in PEEK/CNF composites, when compared with the S of as-received CNFs (-5.3 μV K^-1), is attributed to a slight electron withdrawing from the external layers of CNFs by the PEEK matrix. At temperatures from 30 °C to 100 °C, the σ (T) of PEEK/CNF composites, in contrast to the σ (T) of as-received CNFs, shows a negative temperature effect, understood through the 3D variable-range hopping (VRH) model, as a thermally activated hopping mechanism across a random network of potential wells. Moreover, their nonlinear S (T) follows the same behavior reported before for polypropylene composites melt-processed with similar CNFs at the same interval of temperatures.

Dielectric spectroscopy of melt-extruded polypropylene and as-grown carbon nanofiber composites

In this work, different weight contents of as-grown carbon nanofibers (CNFs), produced by chemical vapor deposition, were melt-extruded with polypropylene (PP) and their morphologic, structure and dielectric properties examined. The morphologic analysis reveals that the CNFs are randomly distributed in the form of agglomerates within the PP matrix, whereas the structural results depicted by Raman analysis suggest that the degree of disorder of the as-received CNFs was not affected in the PP/CNF composites. The AC conductivity of PP/CNF composites at room temperature evidenced an insulator-conductor transition in the vicinity of 2 wt.%, corresponding to a remarkable rise of the dielectric permittivity up to [Formula: see text] 12 at 400 Hz, with respect to the neat PP ([Formula: see text] 2.5). Accordingly, the AC conductivity and dielectric permittivity of PP/CNF 2 wt.% composites were evaluated by using power laws and discussed in the framework of the intercluster polarization model. Finally, the complex impedance and Nyquist plots of the PP/CNF composites are analyzed by using equivalent circuit models, consisting of a constant phase element (CPE). The analysis gathered in here aims at contributing to the better understanding of the enhanced dielectric properties of low-conducting polymer composites filled with carbon nanofibers.

Enhanced Functional Properties of Low-Density Polyethylene Nanocomposites Containing Hybrid Fillers of Multi-Walled Carbon Nanotubes and Nano Carbon Black

In this work, hybrid filler systems consisting of multi-walled carbon nanotubes (MWCNTs) and nano carbon black (nCB) were incorporated by melt mixing in low-density polyethylene (LDPE). To hybrid systems a mixture of MWCNTs and nCB a mass ratio of 1:1 and 3:1 were used. The purpose was to study if the synergistic effects can be achieved on tensile strength and electrical and thermal conductivity. The dispersion state of carbon nanofillers in the LDPE matrix has been evaluated with scanning electron microscopy. The melting and crystallization behavior of all nanocomposites was not significantly influenced by the nanofillers. It was found that the embedding of both types of carbon nanofillers into the LDPE matrix caused an increase in the value of Young’s modulus. The results of electrical and thermal conductivity were compared to LDPE nanocomposites containing only nCB or only MWCNTs presented in earlier work LDPE/MWCNTs. It was no synergistic effects of nCB in multi-walled CNTs and nCB hybrid nanocomposites regarding mechanical properties, electrical and thermal conductivity, and MWCNTs dispersion. Since LDPE/MWCNTs nanocomposites exhibit higher electrical conductivity than LDPE/MWCNTs + nCB or LDPE/nCB nanocomposites at the same nanofiller loading (wt.%), it confirms our earlier study that MWCNTs are a more efficient conductive nanofiller. The presence of MWCNTs and their concentration in hybrid nanocomposites was mainly responsible for the improvement of their thermal conductivity.

Magnetic and Dielectric Properties of Nano- and Micron-BiFeO3/LDPE Composites with Magnetization Treatments

By means of magnetization treatments at ambient temperature and elevated temperatures, the nano- and micron-bismuth ferrate/low density polyethylene (BiFeO₃/LDPE) dielectric composites are developed to explore the material processing method to modify the crystalline morphology, magnetic and dielectric properties. The magnetic field treatment can induce the dipole in the LDPE macromolecular chain which leads to preferred orientation of polyethylene crystal grains to the direction of the magnetization field. The surface morphology of the materials measured by atomic force microscope (AFM) implies that the LDPE macromolecular chains in BiFeO₃/LDPE composites have been orderly arranged and form thicker lamellae accumulated with a larger spacing after high temperature magnetization, resulting in the increased dimension and orientation of spherulites. The residual magnetization intensities of BiFeO₃/LDPE composites have been significantly improved by magnetization treatments at ambient temperature. After this magnetization at ambient temperature, the M_R of nano- and micron-BiFeO₃/LDPE composites approach to 4.415 × 10⁻³ and 0.690 × 10⁻³ emu/g, respectively. The magnetic moments of BiFeO₃ fillers are arranged parallel to the magnetic field direction, leading to appreciable enhancement of the magnetic interactions between BiFeO₃ fillers, which will inhibit the polarization of the electric dipole moments at the interface between BiFeO₃ fillers and the LDPE matrix. Therefore, magnetization treatment results in the lower dielectric constant and higher dielectric loss of BiFeO₃/LDPE composites. It is proven that the magnetic and dielectric properties of polymer dielectric composites can be effectively modified by the magnetization treatment in the melt blending process of preparing composites, which is expected to provide a technical strategy for developing magnetic polymer dielectrics.

The Role of Multiwalled Carbon Nanotubes in the Mechanical, Thermal, Rheological, and Electrical Properties of PP/PLA/MWCNTs Nanocomposites

Polypropylene/polylactic acid (PP/PLA) blend (10–40% of PLA) and PP/PLA/MWCNTs nanocomposites (0.5, 1, and 2 wt% of MWCNTs) were prepared via melt compounding. Scanning electron microscopy revealed a co-continuous PLA phase in the PP/PLA blends with high PLA content. Moreover, the addition of 2 wt% multi-walled carbon nanotubes (MWCNTs) increased the tensile modulus and tensile strength of the PP/PLA40% by 60% and 95%, respectively. A conductive network was found with the addition of 2 wt% MWCNTs, where the electrical conductivity of the PP/PLA increased by nine orders of magnitude. At 2 wt% MWCNTs, a solid network within the composite was characterized by rheological assessment, where the composite turned from nonterminal to terminal behavior. Soil burial testing of the PP/PLA blend within 30 days in natural humus compost soil featured suitable biodegradation, which indicates the PP/PLA blend is as an appropriate candidate for food packing applications.

Antibacterial Activity of TiO2- and ZnO-Decorated with Silver Nanoparticles

This work emphasizes the use of the silver decorative method to enhance the antibacterial activity of TiO2 and ZnO nanoparticles. These silver-decorated nanoparticles (hybrid nanoparticles) were synthesized using sodium borohydride as a reducing agent, with the weight ratio of Ag precursors/oxide nanoparticles = 1:30. The morphology and optical properties of these hybrid nanoparticles were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD) patterns, and UV-Vis spectroscopy. The agar-well diffusion method was used to evaluate their antibacterial activity against both Staphylococcus aureus and Escherichia coli bacteria, with or without light irradiation. The TEM images indicated clearly that silver nanoparticles (AgNPs, 5–10 nm) were well deposited on the surface of nano-TiO2 particles (30–60 nm). In addition to this, bigger AgNPs (<20 nm) were dispersed on the surface of nano-ZnO particles (30–50 nm). XRD patterns confirmed the presence of AgNPs in both Ag-decorated TiO2 and Ag-decorated ZnO nanoparticles. UV-Vis spectra confirmed that the hybridization of Ag and oxide nanoparticles led to a shift in the absorption edge of oxide nanoparticles to the lower energy region (visible region). The antibacterial tests indicated that both oxide pure nanoparticles did not exhibit inhibitory effects against bacteria, with or without light irradiation. However, the presence of AgNPs in their hybrids, even at low content (<40 mg/mL), leads to a good antibacterial activity, and higher inhibition zones under light irradiation as compared to those in dark were observed.

Molecular Dynamics Simulation of Improving the Physical Properties of Polytetrafluoroethylene Cable Insulation Materials by Boron Nitride Nanoparticle under Moisture-Temperature-Electric Fields Conditions

The physical properties in amorphous regions are important for the insulation aging assessment of polytetrafluoroethylene (PTFE) cable insulation materials. In order to study the effect of boron nitride (BN) nanoparticles on the physical properties of PTFE materials under moisture, temperature, and electric fields conditions at the molecular level, the amorphous region models of PTFE, BN/PTFE, water/PTFE, and water/BN/PTFE were respectively constructed by molecular dynamics (MD) simulation. The mechanical properties including Young's modulus, Poisson's ratio, bulk modulus, and shear modulus, along with glass transition temperature, thermal conductivity, relative dielectric constant, and breakdown strength of the four models have been simulated and calculated. The results show that the mechanical properties and the glass transition temperature of PTFE are reduced by the injection of water molecules, whereas the same, along with the thermal conductivity, are improved by incorporating BN nanoparticles. Moreover, thermal conductivity is further improved by the surface grafting of BN nanoparticles. With the increase of temperature, the mechanical properties and the breakdown strength of PTFE decrease gradually, whereas the thermal conductivity increases linearly. The injection of water molecules increases the water content in the PTFE materials, which causes a gradual increase in its relative dielectric constant. This work has shown that this effect is significantly reduced by incorporation of BN nanoparticles. The variation of physical properties for PTFE and its composites under the action of moisture, temperature, and electric fields is of great significance to the study of wet, thermal, and electrical aging tests as well as the life prediction of PTFE cable insulation materials.

Butyl Rubber-Based Composite: Thermal Degradation and Prediction of Service Lifetime

Butyl rubber-based composite (BRC) is one of the most popular materials for the fabrication of protective gloves against chemical and mechanical risks. However, in many workplaces, such as metal manufacturing or automotive mechanical services, its mechanical hazards usually appear together with metalworking fluids (MWFs). The presence of these contaminants, particularly at high temperatures, could modify its properties due to the scission, the plasticization and the crosslinking of the polymer network and thus lead to severe modification of the mechanical and physicochemical properties of material. This work aims to determine the effect of temperature and a metalworking fluid on the mechanical behavior of butyl rubber composite, dealing with crosslinking density, cohesion forces and the elastic constant of BRC, based on Mooney–Rivlin’s theory. The effect of temperature with and without MWFs on the thermo-dynamical properties and morphology of butyl membranes was also investigated. The prediction of service lifetime was then evaluated from the extrapolation of the Arrhenius plot at different temperatures.

Biological Activity and Nanostructuration of Fe3O4-Ag/High Density Polyethylene Nanocomposites

We report here the synthesis of uniform nanospheres-like silver nanoparticles (Ag NPs, 5–10 nm) and the dumbbell-like Fe3O4-Ag hybrid nanoparticles (FeAg NPs, 8–16 nm) by the use of a seeding growth method in the presence of oleic acid (OA)/oleylamine (OLA) as surfactants. The antibacterial activity of pure nanoparticles and nanocomposites by monitoring the bacterial lag–log growth has been investigated. The electron transfer from Ag NPs to Fe3O4 NPs which enhances the biological of silver nanoparticles has been proven by nanoscale Raman spectroscopy. The lamellae structure in the spherulite of FeAg NPs/High Density Polyethylene (HDPE) nanocomposites seems to play the key role in the antibacterial activity of nanocomposites, which has been proven by nanoscale AFM-IR. An atomic force microscopy coupled with nanoscale infrared microscopy (AFM-IR) is used to highlight the distribution of nanoparticles on the surface of nanocomposite at the nanoscale. The presence of FeAg NPs in PE nanocomposites has a better antibacterial activity than that reinforced by Ag NPs due to the faster Ag+ release rate from the Fe3O4-Ag hybrid nanoparticles and the ionization of Ag NPs in hybrid nanostructure.