Formation Of Conductive Network Research Articles

Facile fabrication of three-dimensional thermal conductive composites with synergistic effect of multidimensional fillers

Thermal conductive polymer composites are promising in the application of rapidly developing modern technology. Here, a facile method to fabricate three-dimensional thermal conductive composites with multidimensional fillers was reported. One-dimensional AgNW were used to bridge the randomly dispersing two-dimensional BNNS together in poly(dimethylsiloxane) (PDMS) to form thermal conductive networks. The through-plane thermal conductivity (0.64 W m−1 K−1) of composite 2wt%AgNW/20wt%BNNS/PDMS was 237% higher than that of matrix PDMS (0.19 W m−1 K−1), while the composites still maintained good electrically insulating. A series of theoretical models were used to describe the thermal conductivity as a function of BNNS contents with or without the presence of AgNW. The synergistic effect between BNNS and AgNW was verified from the calculation of interfacial thermal resistance, which decreases from 1.06 × 10–6 m2 K W−1 for system without AgNW to 6.14 × 10–9 m2 K W−1 for system with 2 wt% AgNW. This synergistic strategy via multidimensional fillers supported the methodological possibility of returning to simplicity from various template approaches which were limited in shape and size. It was expected to extend the understanding of available theory and predict the potential formation of 3D thermal conductive networks in other systems with multidimensional fillers.

Graphene enhanced linear low-density polyethylene nanocomposites by premixing and melt compounding

In this study, linear low-density polyethylene/graphene nanoplatelets (LLDPE/GNPs) nanocomposites were prepared from conventional melt-mixing method and our new approach; two-step premix mixing technique. Indirect mixing technique (IDT) was employed to fabricate a premix of LLDPE/ GNPs in the ratio of 80:20 wt%. The effects of GNPs loadings and the processing method of nanocomposites on the mechanical strength, decomposition temperature, crystallinity, electrical impedance and morphology were investigated. Irrespective of processing methods, the prepared nanocomposites exhibited crystalline structure due to the presence of GNPs whilst the degradation temperature was recorded to be increased with GNPs loadings that signified improved thermal stability. The inclusion of GNPs provided electrical impedance ability on LLDPE matrix as a result from the formation of conductive networks of GNPs. LLDPE/GNPs nanocomposites prepared from two-step premix mixing technique showed better mechanical properties than those of melt-mixing method. Apparently, two-step premix mixing of LLDPE/GNPs nanocomposites promoted better dispersion of GNPs in matrix based on SEM images. Our findings have proved that our new, profound technique of preparing premix before mixing could result in enhanced quality of nanocomposites that are potentially useful in packaging or electronic applications.

Negative permittivity behavior in Ti3AlC2-polyimide composites and the regulation mechanism

With the rapid development of metamaterials, percolating composites with negative dielectric constant have become a research hotspot in recent years. In this work, Ti3AlC2-polyimide percolating composites were prepared by mechanical mixing and pressure forming, and their microstructure and dielectric properties were investigated in detail. By controlling the Ti3AlC2 content, an electrical percolation phenomenon appears with the formation of Ti3AlC2 conductive network. The conductive mechanism changed from hoping conduction to metal-like conduction. Above the percolation threshold (68%–72%), real permittivity changes from positive to negative and mainly due to the damped motion of the free electrons. The Drude model analysis showed that the negative permittivity resulted from the plasma-like oscillation of free electrons. The equivalent circuit analysis indicated that the generation of negative permittivity was closely related to the appearance of inductance. This work provided a simple and effective strategy for regulating negative permittivity and promoted its application.

A rational design of core-shell-satellite structured BaTiO3 fillers for epoxy-based composites with enhanced microwave dielectric constant and low loss

With the rapid progress of wireless communication technology, development of composites with high dielectric constant (high-k) and low loss at gigahertz frequency calls for novel materials design strategies. Core-shell-satellite structured BaTiO3 (BT) nanoparticles with polydopamine (PDA) layers and silver (Ag) nanoparticles were herein developed, which were incorporated into epoxy (EP) to prepare a set of composites. Physicochemical properties of modified BT nanoparticles and the dispersion and interface of corresponding modified BT/EP composites were comparatively investigated. The dielectric properties of modified BT/epoxy (EP) nanocomposites with various filler fractions were investigated at 8–12 GHz. It is found that, at the highest filler volume fraction (20 vol%), the dielectric constant of BT-PDA-Ag/EP at 10 GHz reached 8.4, and the loss tangent was also suppressed at 0.024. The polarization and loss mechanisms of the composites were then proposed based on the morphologies and the microstructures of the composites. BT-PDA-Ag promotes interfacial polarization, better dispersion and reduced mismatch, resulting in enhanced dielectric constant and low loss. More importantly, by ensuring a disconnection of the silver particles, PDA hinders the formation of conductive network thus suppressing the dielectric loss. This research provides a novel strategy to prepare high-k and suppressed loss nanocomposites potentially for 5G applications.

Constructing 3D carbon-metal hybrid conductive network in polymer for ultra-efficient electromagnetic interference shielding

In the present work, an effective and versatile strategy is adopted to fabricate ultra-efficient electromagnetic-interference (EMI) shielding composites by constructing perfect 3D carbon-metal hybrid conductive network in polyamide 6 (PA6) matrix. The surface of PA6 granules is first functionalized with expanded graphite (EG) sheets as conductive substrate and subsequently coated with very thin nickel (Ni) layer to form core-shell PA6/EG/Ni complex particles, then highly efficient PA6 shielding composites with well-connected 3D Ni-EG hybrid conductive network can be assembled by a conventional hot compression of the complex particles. The lamellar EG sheets not only serve as deposition template to induce a homogeneous and compact deposition of thin Ni plating, but also facilitate the formation of perfect 3D Ni-EG conductive network by restricting the diffusion between Ni and low-viscosity PA6 melt during hot compression. Benefit from this unique 3D carbon-metal hybrid network and a synergistic effect of the Ni-EG multilayer structure, the PA6/EG/Ni composite shows an ultra-efficient EMI shielding performance of 77.3 dB with extremely low filler content (0.9 vol%). This feasible approach of constructing 3D carbon-metal hybrid network in polymer matrix provides a new possibility for developing affordable high-performance EMI shielding composites for next-generation communication applications.

Carbon fiber skeleton/silver nanowires composites with tunable negative permittivity behavior

With the development of periodic metamaterials, more attention has been paid to negative permittivity behavior due to great potential applications. In this paper, silver nanowires (AgNWs) were introduced to the porous carbon fibers (CFS) by an impregnation process to prepare CFS/AgNWs composites with different content of AgNWs and the dielectric property was investigated. With the formation of conductive network, the Drude-like negative permittivity was observed in CFS/AgNWs composites. With the increase of AgNWs, the connectivity of conductive network became enhanced, the conductivity gradually increases, and the absolute value of the negative dielectric constant also increases to 8.9 × 104, which was ascribed to the enhancement of electron density of the composite material. Further investigation revealed that the inductive characteristic was responsible for the negative permittivity.

Tunable photocatalytic oxidation response of ZnS tethered chitosan-polyaniline composite for the removal of organic pollutants: A mechanistic perspective

Elimination of toxic organic dye pollutants from water using composite photocatalyst adsorbents are studied in detail. The composite preserves all the textures of constituent materials, and circumvents the disadvantages, including photogenerated electron’s speedy recombination, hindrance effect of the photocatalyst and low absorptivity. The present work focused attention on assessing the performance of heterogeneous ZnS tethered chitosan-polyaniline (ZCP) photocatalyst to the degradation of Methylene Blue (MB), and Malachite Green (MG) dyes, both in the visible and UV region. The ternary ZCP composite was found to be stable and the stability of the composite was attributed to the polycationic nature of the chitosan. The prepared ZCP was analysed with XRD, FTIR, SEM, and EDAX with mapping. The UV spectroscopic evaluation reaffirmed the ZCP bandgap as 3.16 eV. The reduced band gap for the ternary composite might be attributed to the formation of conductive networks throughout the chitosan matrix due to uniform dispersion of ZnS in the chitosan matrices as well as the possible grafting of PANI onto chitosan backbone. The photocatalytic result that the greatest mineralizations were 87.3%, and 91.5% for MB and MG dyes with the resultant concentration of dye was 20 mg L−1, ZCP quantity of 0.1 g L−1, under 60 min of light exposure, respectively. The photocatalyst is found to be reusable for up to five cycles. The results affirm that the ZCP matrix could be utilized as a useful photocatalyst for the mineralization of water/wastewater containing dye molecules.

Poly(pyrrole-co-styrene sulfonate)-encapsulated MWCNT/Fe–Ni alloy/NiFe2O4 nanocomposites for microwave absorption

In this work, MWCNTs/Fe–Ni alloy/NiFe2O4 (M/F/N) nanocomposite was prepared via hydrothermal method and then coated with poly(pyrrole-co-styrene sulfonate) (PP@M/F/N) via using in-situ polymerization method. The molar ratios of pyrrole and 3,4-ethylenedioxythiophene co-polymers were adjusted 1:1. The morphological observations confirmed that magnetic nanoparticles were decorated with MWCNTs and finally coated by co-polymers. The microwave absorption results demonstrate that the minimum reflection loss of PP@M/F/N achieved to −85 dB at 12 GHz with effective bandwidth (less than −10 dB) in the range of X band frequency for 2 mm thickness. It was clearly observed that the minimum RL resonance peaks matched at lower frequencies with the increase of thicknesses for PP@M/F/N nanocomposite. According to the results, the formation of conductive network facilitated the electron transport and improved the impedance matching, interfacial polarization, and attenuation ability of the composite. This work illustrated a facile and efficient way to prepared magneto electric nanocomposite as a promising candidate for microwave absorption with a versatile design concept for other types of absorber.

Injectable Hypoxia-Induced Conductive Hydrogel to Promote Diabetic Wound Healing.

Injectable hydrogels with the capability to cast a hypoxic microenvironment is of great potentialities to develop novel therapies for tissue regeneration. However, the relative research still remains at the conceptual phase. Herein, we chose diabetic wound as a representative injury model to explore the actual therapeutic results of tissue injury by injectable hypoxia-induced hydrogels. To enhance recovery and widen applicability, the hypoxia-induced system was incorporated with a conductive network by an original sequentially interpenetrating technique based on the combination of a fast "click chemistry" and a slow enzymatic mediated cross-linking. Hyperbranched poly(β-amino ester)-tetraaniline (PBAE-TA) was cross-linked with thiolated hyaluronic acid (HA-SH) via a thiol-ene click reaction, contributing to the rapid formation of the first conductive network, where vanillin-grafted gelatin (Geln-Van) and laccase (Lac) with a slow cross-linking rate were employed in casting a hypoxic microenvironment. The as-prepared injectable hydrogels possessed both suitable conductivity and sustainable hypoxia-inducing capability to upregulate the hypoxia-inducible factor-1α and connexin 43 expressions of the encapsulated adipose-derived stem cells, which enhanced vascular regeneration and immunoregulation and further promoted the reconstruction of blood vessels, hair follicles, and dermal collagen matrix, eventually leading to the recovery of diabetic rat skin wounds and restoration of skin functions. This work provides a promising strategy to broaden the applicability of diverse hydrogels with a long time-consuming gelation process and to integrate different networks with various biological functions for the therapies of diabetic wounds and other complex clinical symptoms.

Piezoelectric behaviour of hybrid engineered cementitious composites containing shape-memory alloy, steel, and carbon fibres under compressive stress cycles

Fibre hybridisation can improve the performance of Engineered cementitious composites (ECCs). This study examines piezoresistivity, fresh properties, and mechanical behaviour of hybrid ECCs developed through the combination of polyvinyl alcohol (PVA) with shape memory alloy fibres (SMAFs), steel fibres (SFs), and carbon fibres (CFs) individually. The distribution of CFs and the formation of conductive networks within hybrid ECCs containing CFs were also analysed using scanningelectron microscopy. Compared to other composites containing CFs, the hybrid ECC with 0.6% CFs exhibited the best piezoresistive behaviour under compressive stress cycles since it showed the highest correlation coefficient between fractional change in resistivity (FCR) and strain, a narrower 98% prediction interval, and less noisy electrical signals. SEM images of this composite revealed that CFs were in contact in large scale and formed cross-linked clusters, indicating that the CF dosage was above the percolation threshold. In contrast to the composites containing CFs, hybrid ECCs with SMAFs and SFs exhibited an irreversible increase in resistivity, especially in wet condition, due to the polarisation effect. However, the hybrid usage of SMAFs or SFs with PVA significantly enhanced the flexural performance of ECC, whereas its impact on the first-cracking strength of ECCs was insignificant. In contrast, CFs enhanced the first-cracking strength at all CFs contents studied here and increased the flexural strength of composites at CFs content of 0.1% and 0.2%., beyond which the ultimate flexural strength decreased.

Analytical modeling and experimentally optimizing synergistic effect on thermal conductivity enhancement of polyurethane nanocomposites with hybrid carbon nanofillers

AbstractCombining various carbon nanofillers with different dimensions can lead to a synergistic effect through the formation of an efficient conductive network. Hybrid polyurethane (PU) nanocomposites containing multi‐walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) were fabricated to study experimental and theoretical aspects of thermal conductivity (TC) enhancement. The optimization of hybrid nanofillers combinations was done to synergically enhance the TC using various types of graphene, nanofillers concentrations and ratios. A synergistic thermal conductivity improvement with MWCNTs and GNPs was confirmed at low nanofillers contents. The TC of hybrid nanocomposite at 0.25 wt% is approximately equivalent to the TC of individual nanofillers at 0.75 wt%. An analytical model for the effective thermal conductivity of single and hybrid nanocomposites was considered with variables of volume fraction, interfacial thermal resistance, straightness of the nanofillers and the percolation effect, in which the predictions of the modified models agreed with the experimental results.

Electrical properties of anisotropic graphene/PDMS composites induced by aligned ferromagnetic particles

Graphene nanoplate (GNP) is a two-dimensional plate-like carbon material with high aspect ratio and excellent electrical conductivity. It is one of the most commonly used fillers for conductive polymer composites (CPCs), which have potential applications in flexible electrodes and sensors. The electrical properties of the CPCs particularly depend on the microstructure of GNP networks. The electrical conductivity of the CPCs leaps in several magnitude levels when the graphene concentration reaches a critical value, which is defined as the percolation threshold. For ordinary isotropic CPCs, the percolation threshold is relatively high, which leads to inferior performance with poor mechanical and electrical properties. Aligning the graphene plates is an effective method to reduce the percolation threshold of the CPCs. Carbonyl iron particles (CIPs) are easily aligned to form chain-like structures when a magnetic field is applied. In this work, CIPs and GNPs are mixed with polydimethylsiloxane (PDMS), and the hybrid is cured under a magnetic field of 0.5 T. The alignment of CIPs induces the GNPs in the PDMS to orientate in a certain direction under the applied magnetic field generating anisotropic structures. Both isotropic and anisotropic structured GNPs/PDMS composites are prepared with various GNP concentrations. The microstructure and electrical conductivity of the GNPs/PDMS composites are investigated by experimental methods. It is found that anisotropic graphene networks are formed and the percolation threshold of the anisotropic composites is 0.15 vol%, compared to that of the isotropic composites which is 0.85 vol%. The alignment of GNPs significantly reduces the percolation threshold. Furthermore, a plate lattice model is proposed to reveal the effect of the alignment of GNPs on the formation of conductive networks. With the increase of the alignment degree of GNPs, the percolation threshold decreases significantly, which is consistent with the experimental results.

Facile synthesis of Vulcan XC-72 nanoparticles-decorated halloysite nanotubes for the highly sensitive electrochemical determination of niclosamide

We report a scalable and controllable ultrasound-assisted strategy for the preparation of Vulcan XC-72 nanoparticles-decorated halloysite nanotubes (HNTs@VXC-72), which was applied to modify glassy carbon electrode (GCE) for the highly sensitive electrochemical determination of niclosamide (NA). For the HNTs@VXC-72 nanocomposite, VXC-72 nanoparticles with excellent electrical conductivity and good dispersing property contributed to the formation of the interconnected conductive network; HNTs possessed good adsorption performance and promoted the electrochemical redox reaction. The research results showed that the combination of VXC-72 nanoparticles and HNTs produced the effect of synergistic enhancement. The HNTs@VXC-72/GCE sensor could show a relatively low detection limit of 3.28 nM in the great linear NA concentration range of 0.01–1 µM. When used for the NA determination in food samples, the HNTs@VXC-72/GCE sensor exhibited good practical feasibility with low RSD and acceptable recoveries, which provided a promising NA determination approach to ensure food safety.

Proton mobility in metallic copper hydride from high-pressure nuclear magnetic resonance

Atomic and electronic structures of Cu2H and CuH have been investigated by high pressure NMR spectroscopy, X-ray diffraction and ab-initio calculations. Metallic Cu2H was synthesized at a pressure of 40 GPa, and semi-metallic CuH at 90 GPa, found stable up to 160 GPa. Experiments and computations suggest the formation of a metallic 1H-sublattice as well as a high 1H mobility of ~10-7 cm2/s in Cu2H. Comparison of Cu2H and FeH data suggests that deviations from Fermi gas behavior, formation of conductive hydrogen networks, and high 1H mobility could be common features of metal hydrides.

Targeted design and analysis of microwave absorbing properties in iron-doped SiCN/Si3N4 composite ceramics

The SiCN(Fe)/Si3N4 composite ceramics containing C, β-SiC and α-Fe were designed by impregnating polysilazane followed by pyrolysis at 1–5 times with porous silicon nitride matrix. After the heat treatment, these new phases gradually formed and filled in the pores of the matrix to form a large whole. They bond together to facilitate the formation of conductive networks, which can improve the storage and transport capacity of the charge, thus improving the dielectric properties of the material. In this way, the highest dielectric and magnetic loss tangent values were achieved as 0.49 and 0.29 after third and fourth cycles, respectively. The electromagnetic wave can be absorbed ~80–90% in the range of 8–18 GHz with the thickness of 2 mm. The minimum reflectivity was −12.5 dB at 16 GHz with the thickness of 5 mm, showing >90% electromagnetic wave absorption at this frequency.

Highly orientated graphene/epoxy coating with exceptional anti-corrosion performance for harsh oxygen environments

Herein, we designed a spin coating method and fabricated highly orientated graphene/epoxy (OG/EP) coating with long-term anti-corrosion performance. Surprisingly, the impedance at 0.01 Hz of OG/EP coating still remained at a relatively high value after 7 days of immersion in 3 MPa pure O2 and 3.5 wt% NaCl coupling environment, which was about 103 and 8 × 105 times higher than pure epoxy (Spin-EP and Spray-EP) and randomly arranged graphene/epoxy coatings’, respectively. The protection mechanism of OG/EP coating is interpreted as the orientation of graphene, maximizing the barrier effect of graphene and avoiding the formation of graphene conductive network.

Electrical properties of carbon nanotube/liquid metal/rubber nanocomposites

Carbon nanotube (CNT)/rubber nanocomposites have wide applications in wearable devices and robotics, as stretchable conductors or sensitive/flexible piezoresistive sensors. However, the modification and optimization of the electrical properties of these nanocomposites are highly dependent on the dispersion quality of CNTs, and more severally, the high dosage of CNTs could inevitably increase the modulus of rubber, which limits their interaction with soft materials, such as human tissue. A liquid metal (LM), such as eutectic gallium indium, can be considered as a soft and conductive additive to increase the conductivity of rubber. Here, we investigate the modification of the electrical and mechanical properties of CNT/rubber nanocomposites by LMs. We found that LMs are well dispersed in the rubber matrix with the average size increasing with its loading. Wrinkles formed on LM droplets, indicating that the oxide layer was subjected to compressive stress during the polymerization of rubber. Although the conductivity of the CNT/rubber nanocomposites can be improved by about 328% at 10 vol. % of LMs with negligible loss of mechanical properties, further increasing the loading of LMs would decrease the conductivity, suggesting their limited contribution for the conductive network formation in the rubber matrix.

Thermoplastic Polyurethane/Lead Zirconate Titanate/Carbon Nanotube Composites with Very High Dielectric Permittivity and Low Dielectric Loss

Ternary composites of flexible thermoplastic polyurethane (TPU), lead zirconate titanate (PZT), and multiwalled carbon nanotubes (MWCNTs) with very high dielectric permittivity (εr) and low dielectric loss (tan δ) are reported. To assess the evolution of dielectric properties with the interactions between conductive and dielectric fillers, composites were designed with a range of content for PZT (0–30 vol%) and MWCNT (0–1 vol%). The microstructure was composed of PZT-rich and segregated MWCNT-rich regions, which could effectively prevent the formation of macroscopic MWCNT conductive networks and thus reduce the high ohmic loss. Therefore, εr increased by a maximum of tenfold, reaching up to 166 by the addition of up to 1 vol% MWCNT to TPU/PZT. More importantly, tan δ remained relatively unchanged at 0.06–0.08, a similar range to that of pure TPU. εr/tan δ ratio reached 2870 at TPU/30 vol% PZT/0.5 vol% MWCNT, exceeding most of the reported values. This work demonstrates the potential of three-phase polymer/conductive filler/dielectric filler composites for efficient charge storage applications.

Effect of direct–current biasing on the adjustable radio-frequency negative permittivity characteristics of Bi2SiO5/multiwall carbon nanotube metacomposites

Multiwall carbon nanotube (MWCNT) based metacomposites with negative permittivity have received significant interest over the past decade due to their unique electromagnetic properties. Here, markedly percolating Bi2SiO5 (BSO)/MWCNT metacomposites with adjustable negative permittivity were prepared by the facile hydrothermal method. Three-dimensional conductive networks formed by interconnected MWCNT are present in BSO/MWCNT metacomposites with 10 and 20 wt% of MWCNT. The detailed microstructure and resistivity studies of the metacomposites led to realize that the adjustable negative permittivity of the BSO/MWCNT metacomposites attributes to the low-frequency plasmon resonance of free Drude carriers. In this work, the effect of the direct-current biasing voltage in the radio frequency region is investigated on the negative permittivity characteristics. For below percolation threshold (fc) metacomposites, the Maxwell-Wagner polarization effects increase in low-frequency region immediately after dc bias is applied. In case of above percolation threshold (fc) metacomposites, the Drude free carrier concentration increases due to the formation of conductive network among MWCNT led to the rise of negative permittivity values in the low frequency region. This work provides a novel strategy for the adjustment of the negative permittivity value, which can expand the potential application in the field of sensors based on the changes in permittivity properties.

Tuning the Electrically Conductive Network of Grafted Nanoparticles in Polymer Nanocomposites by the Shear Field

Controlling the formation of the conductive network in the polymer nanocomposites (PNCs) is very meaningful to enhance their electrical property. In this work, we investigated the effect of grafted nanoparticles (NPs) on the conductive probability of PNCs in the quiescent state as well as under the shear field via a coarse-grained molecular dynamics simulation. It is found that the smallest percolation threshold is realized at the moderate grafting density, the moderate length of grafted chains or the moderate interaction between grafted chains and free chains. Corresponding to it, the dispersion state of NPs varies from the contact aggregation to the uniform dispersion. By analyzing the connection mode among NPs, the probability of NPs which connect three other ones reaches the maximum value at their moderate dispersion state which is responsible for the optimal conductive probability. In addition, the main cluster size is characterized to better understand the conductive network which is consistent with the percolation threshold. It is interesting to find that the percolation threshold is smaller under the shear field than under the quiescent state. The shear field induces more NPs which connect three other ones. This benefits the formation of the new conductive network. Meanwhile, the anisotropy of the conductive probability is reduced with increasing the grafting density. In summary, this work provides a clear picture on how the conductive network of grafted NPs evolves under the shear field.