Graphene-based Polymer Composites Research Articles

Fabrication of amino and fluorine functionalized graphene-based polymer composites to enhance the electromechanical conversion efficiency of TENGs for energy-harvesting applications

The two main factors hindering the practical utilization of triboelectric nanogenerators (TENGs) are low power density and high internal impedance. To address this issue, TENGs with high electromechanical conversion efficiency must be developed. Several techniques have been investigated to improve the TENGs output performance, including surface modifications (physical or chemical) and embedded charge-trap nanomaterials (dielectric or conductive). Herein, we introduce the novel amino-functionalized reduced graphene oxide (AFGO) and graphite-fluorinated polymer (FG) pillars to enhance the tribo-positivity and tribo-negativity of polyurethane (PU) and Ecoflex (EC), respectively. The surface positive-potential of PU is increased almost 2.2 times (from 201 V to 480 V) and negative-potential of Ecoflex is increased 2.1 times (from −848 V to −1813 V) with incorporating AFGO and FG pillars. Functionalized graphene and graphite-based pillars synergistically enhance surface charges (owing to the presence of –NH2 and -F terminating groups) and minimize triboelectric loss (owing to their conductive nature). The effects of the AFGO and FG contents on the electrical performance were studied systematically. The optimized PUAFGO2/EC15FG-TENG exhibited the maximum electrical output performance with an open-circuit potential of 434 V, a short-circuit current of 11. 2 µA, a power density of 1.18 Wm−2 at a load of 40 MΩ, and a charge density of 17.5 µCm−2. The PUAFGO2/EC15FG-TENG showed a mechanical conversion efficiency of 95% and successfully operated 33 LEDs and a stopwatch. Owing to this effectivity, even under low pressures, with a high sensitivity of 9.5 VPa−1 and high mechanical stability, the proposed TENG device could be used as a biomechanical energy harvester in the near future.

Occupational Exposure during the Production and the Spray Deposition of Graphene Nanoplatelets-Based Polymeric Coatings.

Graphene-based polymer composites are innovative materials which have recently found wide application in many industrial sectors thanks to the combination of their enhanced properties. The production of such materials at the nanoscale and their handling in combination with other materials introduce growing concerns regarding workers' exposure to nano-sized materials. The present study aims to evaluate the nanomaterials emissions during the work phases required to produce an innovative graphene-based polymer coating made of a water-based polyurethane paint filled with graphene nanoplatelets (GNPs) and deposited via the spray casting technique. For this purpose, a multi-metric exposure measurement strategy was adopted in accordance with the harmonized tiered approach published by the Organization for Economic Co-operation and Development (OECD). As a result, potential GNPs release has been indicated near the operator in a restricted area not involving other workers. The ventilated hood inside the production laboratory guarantees a rapid reduction of particle number concentration levels, limiting the exposure time. Such findings allowed us to identify the work phases of the production process with a high risk of exposure by inhalation to GNPs and to define proper risk mitigation strategies.

Dynamic diffusion of water inside graphene-reinforced PU/PTFE coatings: A molecular dynamics approach

Polymers are extensively used in various applications due to their excellent properties. Recently, graphene-based polymer composites have gotten significant attention due to their superior barrier properties to corrosive media. Although there are lots of experimental studies on graphene-based composites, there are very few works available at the atomistic level using molecular dynamics. The present work investigates the role of temperature on the diffusion of water and the effect of graphene-reinforcement in the polyurethane (PU) and polytetrafluoroethylene (PTFE). The results showed an increase in the diffusion at higher temperatures due to an increase in the mobility of polymeric chains at higher temperatures and hence a smooth path for the travel of water molecules. There is a significant decrease in the diffusion of water molecules in the graphene-reinforced systems when compared with neat PU and PTFE systems. The decrement in the diffusion of water in the range of 273 K to 350 K was around 79–93% for graphene-reinforce PU systems and around 58–62% in the case of graphene-reinforced PTFE systems.

Progressing of a power model for electrical conductivity of graphene-based composites

This work presents a power equation for the conductivity of graphene-based polymer composites by the tunneling length, interphase deepness and filler size. The impressions of these factors on the effective concentration and percolation beginning of graphene nano-sheets in nanocomposites are also expressed. The developed equations for percolation beginning and conductivity are examined by the experimented data of some examples, which can guesstimate the interphase depth, tunneling size and percolation exponent. Besides, the impacts of numerous factors on the percolation beginning and conductivity are designed. The developed equation for percolation beginning shows the formation of thick interphase and large tunnels in the reported samples. So, disregarding of tunneling and interphase spaces in polymer graphene nanocomposites overpredicts the percolation beginning. Additionally, the developed model presents the acceptable calculations for the conductivity of samples. Among the mentioned parameters, the concentration and graphene conductivity in addition to the interphase depth induce the strongest effects on the conductivity of composites.

Crystallization and melting of polymer chains on graphene and graphene oxide.

This study employs all-atomistic (AA) molecular dynamics (MD) simulations to investigate the crystallization and melting behavior of polar and nonpolar polymer chains on monolayers of graphene and graphene oxide (GO). Polyvinyl alcohol (PVA) and polyethylene (PE) are used as representative polar and nonpolar polymers, respectively. A modified order parameter is introduced to quantify the degree of two-dimensional (2D) crystallization of polymer chains. Our results show that PVA and PE chains exhibit significantly different crystallization behavior. PVA chains tend to form a more rounded, denser, and folded-stemmed lamellar structure, while PE chains tend to form an elongated straight pattern. The presence of oxidation groups on the GO substrate reduces the crystallinity of both PVA and PE chains, which is derived from the analysis of modified order parameter. Meanwhile, the crystallization patterns of polymer chains are influenced by the percentage, chemical components, and distribution of the oxidation groups. In addition, our study reveals that 2D crystalized polymer chains exhibit different melting behavior depending on their polarity. PVA chains exhibit a more molecular weight-dependent melting temperature than PE chains, which have a lower melting temperature and are relatively insensitive to molecular weight. These findings highlight the critical role of substrate and chain polarity in the crystallization and melting of polymer chains. Overall, our study provides valuable insights into the design of graphene-based polymer heterostructures and composites with tailored properties.

Highly dispersed graphene nanoplatelets in polypropylene composites by employing high-shear stress for enhanced dielectric properties and frequency-selective electromagnetic interference shielding capability

Although graphene nanoplatelets (GNPs) are currently receiving significant interest as a filler for polymer composites, the issue of agglomeration is yet to be overcome for their wide applications. Herein, the high-shear extrusion technique was thoroughly investigated to effectively disperse GNPs in a polypropylene (PP) matrix with a content of 3 wt%. The screw rotation speed was controlled in the range of 1000–3000 rpm, which is extremely high corresponding to the shear rate of 733–2199 s−1 that should be compared with 200 rpm and 99 s−1 of a conventional extruder, respectively. As the shear rate increased, the size of GNP agglomerates decreased from several microns to ca. 250 nm. This size reduction resulted in the significant enhancement of dielectric loss, owing to the strong interfacial polarization at the interfaces between the GNPs and PP matrix. Furthermore, frequency-selective characteristics in electromagnetic interference shielding could be controlled in the wide frequency spectrum covering the X- and Ka-bands by adjusting the shear rates providing different aperture sizes specified by the interstitial distances of GNPs. Altogether, the developed GNP/PP nanocomposites and their methodology have remarkable potential as promising solutions for graphene-based polymer composites.

A fundamental study of improving thermal interface connection by using silane modified, in-situ formed silver-graphene fillers in epoxy polymers for future semiconductor device packaging

Over the past half-century, the increase of on-chip power and on-chip integration density has created new thermal management challenges for 2.5D/3D semiconductor packaging. High-performance thermal management materials in electronic encapsulation are very important to ensure the performance and reliability of the electronic devices. Graphene-based polymer composites have attracted much attention due to the ultrahigh thermal conductivity and large surface area of graphene. However, graphene nanosheets easily aggregate and lack functional groups on their surfaces, leading to phonon scattering within the interfaces. In this work, silver nanoparticles are in-situ formed on the graphene surface by a facile method, then the graphene-silver nanofillers are modified by (3-Mercaptopropyl)trimethoxysilane (MPTS). MPTS reacts with silver nanoparticles to connect them with epoxy. Also, silver nanoparticles on the surface of graphene can fuse together to form metallurgical joints that connect graphene nanosheets.With the fundamental understanding of sintering mechanisms and reducing two types of thermal interfacial resistances (filler-filler and filler-epoxy interface resistances) simultaneously, the resultant epoxy nanocomposites achieve a high through-plane thermal conductivity of 0.99 W/mK at 8 wt% loading. This corresponds to a 465.7% increase in thermal conductivity as compared to that of neat epoxy. Also, the nanocomposites present a low CTE and high thermal stability. They show strong cooling capability and heat dissipation as thermal interface materials (TIMs) through both experimentation and simulation, providing a promising new insight into thermal management materials to meet the demands of next generation high-power and high-density semiconductor packaging.

Graphene-reinforced epoxy powder coating to achieve high performance wear and corrosion resistance

The corrosion and wear resistance of organic coatings are the key factors to maintain their good function. Graphene-based polymer composites have attracted incredible attention owing to their superior physicochemical properties than polymers. In this study, the effect of graphene nanosheet (G) additives on the microstructure, adhesion behaviors, anti-wear performance and corrosion resistant of epoxy powder coatings (EP) were systematically investigated. Field emission scanning electron microscope (FESEM) results verified that the mild addition of G could enhance the compactness of EP and reduced microstructure defects such as cracks, cavities, and voids. The adhesion and tribological results confirmed that the graphene-contained epoxy powder composite coatings (G/EP) could demonstrate significant improvement compared to the EP, which potentially attributed to the high mechanical and self-lubrication properties of G nanoflakes. In particular, the electrochemical and salt spray evaluation revealed that the enhanced physical barrier protection performance and outstanding anti-corrosion capacity of the G/EP composite coating containing 0.4 wt% G. The current study provides a promising metal protection strategy for the development of graphene-enhanced organic powder coatings applied in mechanical-corrosion coupling environments. This article reveals for the first time that graphene nanosheets enhance the interfacial adhesion strength of organic powder coatings, as well as the effect on wear and electrochemical performance.

Electronic Structure and External Electric Field Modulation of Polyethylene/Graphene Interface

Polymer nanocomposites can serve as promising electrostatic shielding materials; however, the underlying physical mechanisms governing the carrier transport properties between nanofillers and polymers remain unclear. Herein, the structural and electronic properties of two polyethylene/graphene (PE/G) interfaces, i.e., type-H and type-A, have been systematically investigated under different electric fields using first principle calculations. The results testify that the bandgaps of 128.6 and 67.8 meV are opened at the Dirac point for type-H and type-A PE/G interfaces, respectively, accompanied by an electron-rich area around the graphene layer, and a hole-rich area around the PE layer. Moreover, the Fermi level shifts towards the valence band maximum (VBM) of the PE layer, forming a p-type Schottky contact at the interface. Upon application of an electric field perpendicular to the PE/G interface, the Schottky contact can be transformed into an Ohmic contact via the tuning of the Schottky barrier height (SBH) of the PE/G interface. Compared with the A-type PE/G interfaces, the H-type requires a lower electric field to induce an Ohmic contact. All these results can provide deeper insights into the conduction mechanism of graphene-based polymer composites as field-shielding materials.

Graphene-Based Polymer Composites for Flexible Electronic Applications.

Graphene-based nanomaterials have gained a lot of interest over the last years in flexible electronics due to their exceptional electrical, mechanical, and optoelectronic properties, as well as their potential of surface modification. Their flexibility and processability make them suitable for electronic devices that require bending, folding, and stretching, which cannot be fulfilled by conventional electronics. These nanomaterials can be assembled with various types of organic materials, including polymers, and biomolecules, to generate a variety of nanocomposites with greater stretchability and healability, higher stiffness, electrical conductivity, and exceptional thermal stability for flexible lighting and display technologies. This article summarizes the main characteristics and synthesis methods of graphene, its oxidized form graphene oxide (GO), and reduced GO derivative, as well as their corresponding polymeric composites, and provides a brief overview about some recent examples of these nanocomposites in flexible electronic applications, including electrodes for solar cells and supercapacitors, electronic textiles, and transistors.

Synthesis of Graphene-based Polymer Nanocomposites and comparison of properties

Biodegradable polymers promise a more sustainable future. Among a wide range of biopolymers utilized, Poly Lactic Acid (PLA) possess better biomechanical and functional characteristics and is used in various level of applications. However, to have better suitability for biomedical applications, it is necessary to enhance the overall performance of PLA such as biodegradability, porosity, and mechanical properties. Reinforcement of the matrix material with nanofiller is a commonly used method to achieve this. Graphene is the most versatile material with exotic mechanical, electrical, and thermal properties. Its combination with polymers can create wonders. Graphene-based polymer composites exhibit potential use in various fields that include energy storage, biomedical use, and environmental applications. In this work, nanocomposites of PLA with graphene derivatives like Graphene Oxide (GO) and reduced Graphene Oxide (rGO) were fabricated by the solvent casting method. The composites' biological and mechanical properties were investigated and compared. Results demonstrate that the incorporation of GO and rGO enhanced the properties of PLA. The mechanical parameters of the composites with rGO were higher than those of the composites with GO in terms of tensile strength and Young's modulus. A reduction in elongation at break was observed for composites reinforced with rGO. PLA/rGO composites exhibit higher mechanical and biological properties than PLA/GO composites. The developed nanocomposite will be a promising competitor in the research arena with potential applications.

Prospect of DFT Utilization in Polymer-Graphene Composites for Electromagnetic Interference Shielding Application: A Review.

The improvement in current materials science has prompted a developing need to capture the peculiarities that determine the properties of materials and how they are processed on an atomistic level. Quantum mechanics laws control the interface among atoms and electrons; thus, exact and proficient techniques for fixing the major quantum-mechanical conditions for complex many-particle, many-electron frameworks should be created. Density functional theory (DFT) marks an unequivocal advance in these endeavours. DFT has had a rapid influence on quintessential and industrial research during the last decade. The DFT system describes periodic structural systems of 2D or 3D electronics with the utilization of Bloch’s theorem in the direction of Kohn–Sham wavefunctions for the significant facilitation of these schemes. This article introduces and discusses the infinite systems modelling approach required for graphene-based polymer composites or their hybrids. Aiming to understand electronic structure computations as per physics, the impressions of band structures and atomic structure envisioned along with orbital predicted density states are beneficial. Convergence facets coupled with the basic functions number and the k-points number are necessary to explain for every physicochemical characteristic in these materials. Proper utilization of DFT in graphene-based polymer composites for materials in EMI SE presents the potential of taking this niche to unprecedented heights within the next decades. The application of this system in graphene-based composites by researchers, along with their performance, is reviewed.

A Comprehensive Review on Oxygen Reduction Reaction in Microbial Fuel Cells

The focus of microbial fuel cell research in recent years has been on the development of materials, microbes, and transfer of charges in the system, resulting in a substantial improvement in current density and improved power generation. The cathode is generally recognized as the limiting factor due to its high-distance proton transfer, slow oxygen reduction reaction (ORR), and expensive materials. The heterogeneous reaction determines power generation in MFC. This comprehensive review describes-recent advancements in the development of cathode materials and catalysts associated with ORR. The recent studies indicated the utilization of different metal oxides, the ferrite-based catalyst to overcome this bottleneck. These studies conclude that some cathode materials, in particular, graphene-based conductive polymer composites with non-precious metal catalysts provide substantial benefits for sustainable development in the field of MFCs. Furthermore, it also highlights the potentiality to replace the conventional platinum air cathode for the large-scale production of the next generation of MFCs. It was evident from the experiments that cathode catalyst needs to be blended with conductive carbon materials to make cathode conductive and efficient for ORR. This review discusses various antifouling strategies for cathode biofouling and its effect on the MFC performance. Moreover, it also depicts cost estimations of various catalysts essential for further scale-up of MFC technology.

A review on the electrical and electrochemical behavior of composites based on carbon nanotube, graphene and their derivatives

Today, we stand at the edge of exploring carbon nanotube (CNT) and graphene based polymer composites and supercapacitors as next generation multifunctional materials. Supercapacitor materials have been alternative energy source in modern electronics era. Due to their excellent electrical, mechanical and thermal properties, CNTs, graphene and their derivatives have been most promising nanofillers in different fieldsof applications. Inthis review, we have focused electrical conductivity of the polymer composites as well as supercapacitor behavior of composites based on CNTs, graphene and their derivatives. To enhance the electrical and supercapacitor properties of the composites, nanofillers are functionalized or chemically modified through different techniques. Here, we have discussed the structure, preparation,electrical and supercapacitor properties of different composites based on CNTs, graphene and their derivatives along with detailed reported scientific literature.Copyright © 2018VBRI Press

3D structured graphene fluoride-based epoxy composites with high thermal conductivity and electrical insulation

Graphene-based polymer composites possess high thermal conductivity, unfortunately, the high electrical conductivity of these composites limits their application in electronic devices. To address this issue, we report on the thermally conducting yet electrically insulating graphene fluoride (GF) based epoxy composites. GF was coated on cell walls of polyurethane foam (PUF) by a cyclic assembly deposition process, and the PUF@GF foam was subsequently compressed and infiltrated with epoxy resin. The resultant PUF@GF/epoxy composite exhibited a thermal conductivity of 9.68 W·m−1·K−1 at 8.04 vol% of GF loading which was 51-folds higher than that of neat epoxy. The significant enhancement in thermal conductivity is attributed to the effective formation of 3D thermoconductive pathways of GF in epoxy matrix. Additionally, the PUF@GF/epoxy composites possess an electrical insulating property (10−9 S·m−1). This approach exhibits a cost-effective method to fabricate the thermoconductive composites with electrical insulation that could be applied for thermal management in electronic applications.

3D percolation modeling for predicting the thermal conductivity of graphene-polymer composites

Graphene-based polymer composites exhibit a microstructure formed by aggregates within a matrix with enhanced thermal conductivity. We develop a percolation-based computational method, based on the multiple runnings of the shortest path iteratively for ellipsoidal particles to predict the thermal conductivity of such composites across stochastically-developed channels. We analyze the role of the shape and the aspect ratio of the flakes and we predict the onset of percolation based on the density and particle dimensions. Consequently, we complement and verify the conductivity trends via our experiments by inclusion of graphene aggregates and fabrication of graphene-polymer composites. The analytical development and the numerical simulations are successfully verified with the experiments, where the prediction could explain the role of larger set of particle geometry and density. Such percolation-based quantification is very useful for the effective utilization and optimization of the equivalent shape of the graphene flakes and their distribution across the composite during the preparation process and application.

Lightweight, few-layer graphene composites with improved electro-thermal properties as efficient heating devices for de-icing applications

Conductive polymer-based composites with electro-thermal properties are gaining great interest in several challenging technological applications. They are more and more employed as integrated heating devices within smart buildings or de-icing materials for application spanning from the aerospace sector to that of civil engineering. Their lightweight character along with high thermal efficiency and moderate production costs, make them highly attractive alternative to the use of classical electrothermal systems based on costly and heavier metals. Here we describe a convenient approach to the preparation of few-layer graphene-based (FLG) polymer composites obtained from the surface coating of selected polymer matrices with an electrically conductive and thin FLG “skin”. We demonstrated that low FLG concentrations at the outmost polymer surface, together with an excellent and homogeneous surface adhesion, allowed to get fast-responsive and lightweight heatable devices while keeping unchanged the properties of the underlying polymers. A controlled low-temperature post-treatment of the composites ensured an extremely high adhesion of FLG sheets to the hosting polymer substrate. The as-prepared composites have shown fast on/off heating response and exceptional performance once employed as lightweight and low-power heating devices with de-icing properties.

Enhancing sensitivity of QCM for dengue type 1 virus detection using graphene-based polymer composites

Graphene oxide-molecularly imprinted polymer composites (GO-MIP) have attracted significant attention as recognition materials in sensing due to their outstanding properties in terms of electrical and thermal conductivity, high mechanical modulus, and the comparably straightforward way to functionalize them. The aim of this study was to design a MIP-based sensor recognition material and enhance its sensitivity by blending it with GO for sensing a harmful dengue hemorrhagic fever pathogen, namely the dengue type 1 virus (DENV-1). Polymer composites comprising GO incorporated to an acrylamide (AAM)/methacrylic acid (MAA)/methyl methacrylate (MMA)/N-vinylpyrrolidone (VP) copolymer were synthesized and compared to the “pure” MIP, i.e., the copolymer without GO. The pure polymer revealed a zeta potential of + 9.9 ± 0.5 mV, whereas GO sheets prepared have a zeta potential of − 60.3 ± 2.7 mV. This results in an overall zeta potential of − 11.2 ± 0.2 mV of the composite. Such polymer composites seem appropriate to bind the positively charged DENV-1 particle (+ 42.2 ± 2.8 mV). GO-MIP coated onto 10-MHz quartz crystal microbalance (QCM) sensors indeed revealed two times sensitivity compared to sensors based on the pure MIP. Furthermore, GO-polymer composites revealed imprinting factors of up to 21, compared to 3 of the pure MIP. When plotting the sensor characteristic in a semilogarithmic way, the composite sensor shows the linear response to DENV-1 in the concentration range from 100 to 103 pfu mL−1. The corresponding limits of detection (S/N = 3) and quantification (S/N = 10) are 0.58 and 1.94 pfu mL−1, respectively. Furthermore, imprinted polymer composites selectively bind DENV-1 without significant interference: DENV-2, DENV-3, DENV-4, respectively, yield 13–16% of DENV-1 signal. The sensor requires only about 15–20 min to obtain a result.Graphical abstract

Advancement in Graphene-Based Materials and Their Nacre Inspired Composites for Armour Applications-A Review.

The development of armour systems with higher ballistic resistance and light weight has gained considerable attention as an increasing number of countries are recognising the need to build up advanced self-defence system to deter potential military conflicts and threats. Graphene is a two dimensional one-atom thick nanomaterial which possesses excellent tensile strength (130 GPa) and specific penetration energy (10 times higher than steel). It is also lightweight, tough and stiff and is expected to replace the current aramid fibre-based polymer composites. Currently, insights derived from the study of the nacre (natural armour system) are finding applications on the development of artificial nacre structures using graphene-based materials that can achieve high toughness and energy dissipation. The aim of this review is to discuss the potential of graphene-based nanomaterials with regard to the penetration energy, toughness and ballistic limit for personal body armour applications. This review addresses the cutting-edge research in the ballistic performance of graphene-based materials through theoretical, experimentation as well as simulations. The influence of fabrication techniques and interfacial interactions of graphene-based bioinspired polymer composites for ballistic application are also discussed. This review also covers the artificial nacre which is shown to exhibit superior mechanical and toughness behaviours.

GO based PVA nanocomposites: tailoring of optical and structural properties of PVA with low percentage of GO nanofillers

Graphene-based polymer composites are gaining interest as a modish class of substance that holds promising angles on diverse applications. In this work, Graphene Oxide (GO) based Polyvinyl Alcohol (PVA) nanocomposites (PVA-GO) have been prepared by employing a facile solution casting method. Low concentrations of GO nanofiller (0.25%, 0.50%, 0.75%, and 1.0%) were used and the result of the use of them over the distinct substantial characteristics of the nanocomposites was evaluated. The different features of the as-synthesized nanocomposites such as optical, structural, chemical, and thermal properties were identified by UV-Vis spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), and Thermo-gravimetric analysis (TGA), respectively. From the structural analysis of the crystallinity of the nanocomposite it is evident that a reduction in crystallinity caused by the amalgamation of the GO nanofiller. FTIR study shows improved interaction between the GO nanofiller and PVA matrix. The incorporation of GO was found to reduce the optical band gap of the nanocomposite both for the direct and indirect transition. The Urbach energy of the nanocomposite increases with the increase of the GO concentration suggests the formation of localized states causing a reduction in the optical band gap. PVA-GO nanocomposites with improved and tunable physical properties synthesized from a simple and economic route may pave a new horizon for polymer-based optoelectronic devices.