Evolution from graphite to graphene elastomer composites

Graphene nanoplatelets on recycled rubber: an experimental study of material properties and mechanical improvements

This study presents an experimental investigation of the mechanical behaviour of recycled rubber pads coated with graphene nanoplatelets. The investigation is part of an effort to develop a novel rubber-based composite that aims to reroute rubber from end-of-life tyres from illegal landfills and incineration back into the market in the form of a novel composite for vibration isolation. Graphene nanoplatelets were deposited on rubber pads via ultrasonic spray coating. The pads were made of a combination of recycled rubber (from tyres) and virgin rubber. A comprehensive analysis of the structural and chemical properties of the graphene coating, ensuring its integrity on the rubber substrate, was performed by combining surface topography, Raman and Fourier-transform infrared (FTIR) spectroscopy. Stacked coated pads were cured and tested dynamically in compression and shear under cyclic loading. Results showed promising improvements in the mechanical properties, in particular, in compressive stiffness and damping of the coated specimens with respect to their uncoated counterparts, laying the foundation for using graphene-enhanced recycled rubber as a novel composite.This article is part of the theme issue 'Celebrating the 15th anniversary of the Royal Society Newton International Fellowship'.

Polymer-Assisted Graphite Exfoliation: Advancing Nanostructure Preparation and Multifunctional Composites

Exfoliated graphite (ExG) embedded in a polymeric matrix represents an accessible, cost-effective, and sustainable method for generating nanosized graphite-based polymer composites with multifunctional properties. This review article analyzes diverse methods currently used to exfoliate graphite into graphite nanoplatelets, few-layer graphene, and polymer-assisted graphene. It also explores engineered methods for small-scale pilot production of polymer nanocomposites. It highlights the chemistry involved during the graphite intercalation and exfoliation process, particularly emphasizing the interfacial interactions related to steric repulsion forces, van der Waals forces, hydrogen bonds, π-π stacking, and covalent bonds. These interactions promote the dispersion and stabilization of the graphite derivative structures in polymeric matrices. Finally, it compares the enhanced properties of nanocomposites, such as increased thermal and electrical conductivity and electromagnetic interference (EMI) shielding applications, with those of neat polymer materials.

Graphene-Based Hybrid Fillers for Rubber Composites

Graphene and its derivatives have been confirmed to be among the best fillers for rubber due to their excellent properties, such as high mechanical strength, improved interface interaction, and strain-induced crystallization capabilities. Graphene rubber materials can be widely used in tires, shoes, high-barrier conductive seals, electromagnetic shielding seals, shock absorbers, etc. In order to reduce the graphene loading and endow more desirable functions to rubber materials, graphene-based hybrid fillers are extensively employed, which can effectively enhance the performance of rubber composites. This review briefly summarizes the recent research on rubber composites with graphene-based hybrid fillers consisting of carbon black, silica, carbon nanotubes, metal oxide, and one-dimensional nanowires. The preparation methods, performance improvements, and applications of different graphene-based hybrid fillers/rubber composites have been investigated. This study also focuses on methods that can ensure the effectiveness of graphene hybrid fillers in reinforcing rubber composites. Furthermore, the enhanced mechanism of graphene- and graphene derivative-based hybrid fillers in rubber composites is investigated to provide a foundation for future studies.

Electrically Conductive Natural Rubber Composite Films Reinforced with Graphite Platelets

Green natural rubber (NR) composites reinforced with synthetic graphite platelets, using alginate as a thickening and dispersing agent, were successfully developed to improve mechanical properties, chemical resistance, and electrical conductivity. The fabrication was performed using a latex aqueous microdispersion process. The research demonstrated the effective incorporation of graphite platelets into the NR matrix up to 60 parts per hundred rubbers (phr) without causing agglomeration or phase separation. Graphite incorporation significantly improved the mechanical strength of the composite films. NR with 60 phr of graphite exhibited the highest Young's modulus of 12.3 MPa, roughly 100 times that of the neat NR film. The reinforcement also strongly improved the hydrophilicity of the composite films, resulting in a higher initial water absorption rate compared to the neat NR film. Moreover, the incorporation of graphite significantly improved the chemical resistance of the composite films against nonpolar solvents, such as toluene. The composite films exhibited biodegradability at about 21% to 30% after 90 days in soil. The electrical conductivity of the composite films was considerably enhanced up to 2.18 × 10-4 S/cm at a graphite loading of 60 phr. According to the improved properties, the developed composites have potential applications in electronic substrates.

Modulating the Configurations of "Gel-Type" Soft Silicone Rubber for Electro-Mechanical Energy Generation Behavior in Wearable Electronics

Electro-mechanical configurations can be piezo-electric transducers, triboelectric generators, electromagnetic induction, or hybrid systems. Our present study aims at developing energy generation through the piezoelectric principle. Gel-type soft SR with Shore A hardness below 30 was used as a versatile material for an elastomeric substrate. Also, multi-wall carbon nanotube (MWCNT), and diatomaceous earth (DE) were used as reinforcing fillers. This "gel-type" soft SR has crosslinking polymer networks with silicone encapsulated within its structure. Mechanical properties such as modulus or stretchability are of utmost importance for such devices based on "gel-type" soft. From the experiments, some of the mechanical aspect's values are summarized. For example, the stretchability was 99% (control) and changes to 127% (3 phr, MWCNT), 76% (20 phr DE), and 103% (20 phr hybrid). From electro-mechanical tests, the output voltage was 0.21 mV (control) and changed to 0.26 mV (3 phr, MWCNT), 0.19 mV (20 phr DE), and 0.29 mV (20 phr hybrid). Moreover, from real-time biomechanical human motion tests in "gel-type" soft-based composites, a relationship among output voltage from machine to human motions was established. Overall, these configurations make them promising against traditional portable devices such as batteries for small power applications such as mobile phones.

Avant-Garde Polymer and Nano-Graphite-Derived Nanocomposites—Versatility and Implications

Graphite (stacked graphene layers) has been modified in several ways to enhance its potential properties/utilities. One approach is to convert graphite into a unique ‘nano-graphite’ form. Nano-graphite consists of few-layered graphene, multi-layered graphene, graphite nanoplatelets, and other graphene aggregates. Graphite can be converted to nano-graphite using physical and chemical methods. Nano-graphite, similar to graphite, has been reinforced in conducting polymers/thermoplastics/rubbery matrices to develop high-performance nanocomposites. Nano-graphite and polymer/nano-graphite nanomaterials have characteristics that are advantageous over those of pristine graphitic materials. This review basically highlights the essential features, design versatilities, and applications of polymer/nano-graphite nanocomposites in solar cells, electromagnetic shielding, and electronic devices.

Printable Graphene-Sustainable Elastomer-Based Cross Talk Free Sensor for Point of Care Diagnostics

Developing sensors for monitoring physiological parameters such as temperature and strain for point of care (POC) diagnostics is critical for better care of the patients. Various commercial sensors are available to get the job done; however, challenges like the structural rigidity of such sensors confine their usage. As an alternative, flexible sensors have been looked upon recently. In most cases, flexible sensors cannot discriminate the signals from different stimuli. While there have been reports on the printable sensors providing cross-talk-free solutions, research related to developing sensors from a sustainable source providing discriminability between signals is not well-explored. Herein, we report the development of a stencil printable composition made of graphene and epoxidized natural rubber. The stencil printability index was vetted using rheological studies. Post usage, the developed sensor was dissolved in an organic solvent at room temperature. This, along with the choice of a sustainable elastomer, warrants the minimization of electronic waste and carbon footprint. The developed material demonstrated good conformability with the skin and could perceive and decouple the signals from temperature and strain without inducing any crosstalks. Using a representative volume element model, a comparison between experimental findings and computation studies was made. The developed sensors demonstrated gauge factors of -506 and 407 in the bending strain regimes of 0-0.04% and 0.04%-0.09%, respectively, while the temperature sensitivity was noted to be -0.96%/°C. The printed sensors demonstrated a multifunctional sensing behavior for monitoring various active physiological parameters ranging from temperature, strain, pulse, and breathing to auditory responses. Using a Bluetooth module, various parameters like temperature and strain could be monitored seamlessly in a smart-phone. The current development would be crucial to open new avenues to fabricate crosstalk-free sensors from sustainable sources for POC diagnostics.

Influence of microstructural alterations of liquid metal and its interfacial interactions with rubber on multifunctional properties of soft composite materials

Liquid metal (LM)-based polymer composites are currently new breakthrough and emerging classes of soft multifunctional materials (SMMs) having immense transformative potential for soft technological applications. Currently, room-temperature LMs, mostly eutectic gallium‑indium and Galinstan alloys are used to integrate with soft polymer due to their outstanding properties such as high conductivity, fluidity, low adhesion, high surface tension, low cytotoxicity, etc. The microstructural alterations and interfacial interactions controlling the efficient integration of LMs with rubber are the most critical aspects for successful implementation of multifunctionality in the resulting material. In this review article, a fundamental understanding of microstructural alterations of LMs to the formation of well-defined percolating networks inside an insulating rubber matrix has been established by exploiting several existing theoretical and experimental studies. Furthermore, effects of the chemical modifications of an LM surface and its interfacial interactions on the compatibility between solid rubber and fluid filler phase have been discussed. The presence of thin oxide layer on the LM surface and the effects and challenges it poses to the adequate functionalization of these materials have been discussed. Plausible applications of SMMs in different soft matter technologies, like soft robotics, flexible electronics, soft actuators, sensors, etc. have been provided. Finally, the current technical challenges and further prospective to the development of SMMs using non‑silicone rubbers have been critically discussed. This review is anticipated to infuse a new impetus to the associated research communities for the development of next generation SMMs.

Ionic liquid dispersed highly conducting polymer electrolyte for supercapacitor application: Current scenario and prospects “ICSEM 2021”

Ionic liquid (IL) is now being considered as a novel contender in the development of highly conducting polymer electrolytes rather than a solvent. It has a significant impact on the electrochemical performance of polymer electrolytes. This study emphasizes the significance of low viscosity IL dispersion within a polymer (PVA) matrix. The electrical, structural and photoelectrochemical properties of the IL-doped polymer electrolyte are discussed in detail. These highly conducting IL doped solid polymer electrolytes show promise towards the development of highly efficient Supercapacitors.

Development and Characterization of High Environmentally Friendly Composites of Bio-Based Polyamide 1010 with Enhanced Fire Retardancy Properties by Expandable Graphite

Bio-based polyamide 1010 was melt-compounded with different percentages (2.5 to 10.0 wt.%) of expandable graphite (EGr) as an environmentally friendly solution to improve the flame retardancy properties. The mechanical, morphological, thermal and fire retardancy properties (among others) are analysed. The novelty of the article lies in the use of fully removable polyamide. The effect of the incorporation of EGr in the properties of this polymer was analysed and characterised. The incorporation of EGr into the PA1010 matrix led to very promising results. Mechanically, the EGr provided increased stiffness and a tensile strength up to 7.5 wt.%, verifying good mechanical performance. The DMTA results also show how the incorporation of EGr in the PA1010 matrix clearly increases the stiffness of the composites over the entire temperature range analysed. In terms of physical properties, water absorption of PA1010 was reduced particularly in the 10% EGr, which reduces the water absorption of PA1010 by 20%. In terms of flame retardant properties, with the incorporation of EGr, a significant reduction in the heat release rate (HRR) values as the concentration of the additive increases and a reduction in the maximum peak heat release rate (pHRR) can be observed for all compounds. In particular, it goes from 934 kW/m2 for neat polyamide to a value of 374 kW/m2 with 10% EGr. Finally, an improvement in the UL-94 rating of the 7.5 and 10% EGr composites was also observed, going from V-2 in the PA to V-1 in these composites.

Infrared Linear Dichroism for the Analysis of Molecular Orientation in Polymers and in Polymer Composites

The mechanical properties of polymeric materials are strongly affected by molecular orientation occurring under processing conditions. Infrared dichroism is particularly well suited for characterizing polymer chain orientation at a molecular level. The usefulness of this technique has been demonstrated through various applications in homopolymers, semi-crystalline polymers, copolymers, polymer blends, as well as in polymer composites. Determination of molecular orientation can be carried out in the mid- and near-infrared ranges and very small dichroic effects can be detected with the use of a photoelastic modulator. Chain orientation in polymer composites is seen to increase with the filler content in the case of a strong interface between the two phases, making possible a quantification of the degree of bonding between the host polymeric matrix and the incorporated inclusions.

Graphene oxide nanocomposites based room temperature gas sensors: A review

Over the last few decades, various volatile organic compounds (VOCs) have been widely used in the processing of building materials and this practice adversely affected the environment i.e. both indoor and outdoor air quality. A cost-effective solution for detecting a wide range of VOCs by sensing approaches includes chemiresistive, optical and electrochemical techniques. Room temperature (RT) chemiresistive gas sensors are next-generation technologies desirable for self-powered or battery-powered instruments utilized in monitoring emissions that are associated with indoor/outdoor air pollution and industrial processes. In this review, a state-of-the-art overview of chemiresistive gas sensors is provided based on their attractive analytical characteristics such as high sensitivity, selectivity, reproducibility, rapid assay time and low fabrication cost. The review mainly discusses the recent advancement and advantages of graphene oxide (GO) nanocomposites-based chemiresistive gas sensors and various factors affecting their sensing performance at RT. Besides, the sensing mechanisms of GO nanocomposites-based chemiresistive gas sensors derived using metals, transition metal oxides (TMOs) and polymers were discussed. Finally, the challenges and future perspectives of GO nanocomposites-based RT chemiresistive gas sensors are addressed.

Preparation of p-Phenylenediamine Modified Graphene Foam/Polyaniline@Epoxy Composite with Superior Thermal and EMI Shielding Performance

With the development of integrated devices, the local hot spot has become a critical problem to guarantee the working efficiency and the stability. In this work, we proposed an innovative approach to deliver graphene foam/polyaniline@epoxy composites (GF/PANI@EP) with improvement in the thermal and mechanical property performance. The graphene foam was firstly modified by the grafting strategy of p-phenylenediamine to anchor reactive sites for further in-situ polymerization of PANI resulting in a conductive network. The thermal conductivity (κ) and electromagnetic interference shielding (EMI) performance of the optimized GF/PANI4:1@EP is significantly enhanced by 238% and 1184%, respectively, compared to that of pristine EP with superior reduced modulus and hardness. Such a method to deliver GF composites can not only solve the agglomeration problem in traditional high content filler casting process, but also provides an effective way to build up conductive network with low density for thermal management of electronic devices.

Piezo-Resistive Properties of Bio-Based Sensor Yarn Made with Sisal Fibre

In this work, a sensor yarn based on a natural sisal yarn containing a non-electro-conductive core impregnated with PVA polymer and coated by PEDOT:PSS polymer as an electro-conductive sheath was investigated. The main objectives include the development of this new sensor yarn as a first step. Then, we look towards the insertion of this sensor yarn into different woven structures followed by the monitoring of the mechanical behaviour of composite materials made with these fibrous reinforcements. The combined effect of the structural geometry and the number of PEDOT:PSS coating layers on the properties of the sensor yarns was investigated. It was found that the number of PEDOT:PSS coating layers could strongly influence the electromechanical behaviours of the sensor yarns. Different methods of characterization were employed on strain-sensor yarns with two and four coating layers of PEDOT:PSS. The piezo-resistive strain-sensor properties of these selected coating layers were evaluated. Cyclic stretching-releasing tests were also performed to investigate the dynamic strain-sensing behavior. The obtained results indicated that gauge factor values can be extracted in three strain regions for two and four coating layers, respectively. Moreover, these strain-sensor yarns showed accurate and stable sensor responses under cyclic conditions. Furthers works are in progress to investigate the mechanism behind these first results of these sisal fibre-based sensors.

Graphene and water-based elastomer nanocomposites - a review

Water-based elastomers (WBEs) are polymeric elastomers in aqueous systems. WBEs have recently continued to gain wide acceptability by both academia and industry due to their remarkable environmental and occupational safety friendly nature, as a non-toxic elastomeric dispersion with low-to-zero volatile organic compound (VOC) emission. However, their inherent poor mechanical and thermal properties remain a drawback to these sets of elastomers. Hence, nano-fillers such as graphene oxide (GO), reduced graphene oxide (rGO) and graphene nanoplatelets (GNPs) are being employed for the reinforcement and enhancement of this set of elastomers. This work is geared towards a critical review and summation of the state-of-the-art developments of graphene enhanced water-based elastomer composites (G-WBEC), including graphene and composite production processes, properties, characterisation techniques and potential commercial applications. The dominant production techniques, such as emulsion mixing and in situ polymerisation processes, which include Pickering emulsion, mini-emulsion and micro-emulsion, as well as ball-milling approach, are systematically evaluated. Details of the account of mechanical properties, electrical conductivity, thermal stability and thermal conductivity enhancements, as well as multifunctional properties of G-WBEC are discussed, with further elaboration on the structure-property relationship effects (such as dispersion and filler-matrix interface) through effective and non-destructive characterisation tools like Raman and XRD, among others. The paper also evaluates details of the current application attempts and potential commercial opportunities for G-WBEC utilisation in aerospace, automotive, oil and gas, biomedicals, textiles, sensors, electronics, solar energy, and thermal management.

Enhancement of Gas Barrier Properties of Graphene Oxide/Poly (Lactic Acid) Films Using a Solvent-free Method

Graphene oxide(GO)/polylactic acid (PLA) nanocomposite, prepared using a solvent-free melt mixing processing, is investigated as a potential oxygen barrier packaging film in this work. In order to disperse GO homogeneously in PLA matrix, hydrophobic silane coupling agent, i.e., γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560), is used to modify the graphene oxide sheets. The modified GO is able to be well bonded to the PLA due to the formation of covalent bonds between the epoxy groups of KH560 and the carboxyl and hydroxyl terminal groups of PLA. Furthermore, the thermal stability of GO is enhanced due to the long alkyl side chain of KH560, which could also increase the crystallinity of PLA. As a result, the crystallinity of PLA is significantly improved because of the linear KH560 chains, which can act as nucleating agents to improve the crystallization. The KH560-GO helps to reduce the O₂ permeability of KH560-GO/PLA composite films via a dual-action mechanism: (1) providing physical barrier due to their native barrier properties, and (2) by resulting in higher degree of crystallinity. The as-prepared KH560-GO0.75/PLA is able to exhibit ca. 33% and ca. 13% decrease in the P_O2 than the neat PLA and GO0.75/PLA film, respectively. Finally, the mechanical properties and impact fractured surfaces indicate that the increase in the tensile strength and elongation at break value of KH560-GO/PLA are due to the strong interfacial adhesion and the strong bonding between the epoxy group of KH560-GO and hydroxyl and carboxyl acid terminal groups of PLA matrix.

Electromechanical Behaviors of Graphene Reinforced Polymer Composites: A Review

Graphene (including its derivatives)-reinforced polymer composites (GRPCs) have been drawing tremendous attention from academic and industrial communities for developing smart materials and structures. Such interest stems from the excellent combination of the mechanical and electrical properties of these composites while keeping the beneficial intrinsic attributes of the polymers, including flexibility, easy processability, low cost and good biological and chemical compatibility. The electromechanical performances of these GRPCs are of great importance for the design and optimization of engineering structures and components. Extensive work has been devoted to this topic. This paper reviews the recent studies on the electromechanical behaviors of GRPCs. First the methods and techniques to manufacture graphene and GRPCs are introduced, in which the pros and cons of each method are discussed. Then the experimental examination and theoretical modeling on the electromechanical behaviors of the nanocomposites are presented and discussed.

Friction, Abrasion and Crack Growth Behavior of In-Situ and Ex-Situ Silica Filled Rubber Composites

The article focuses on comparing the friction, abrasion, and crack growth behavior of two different kinds of silica-filled tire tread compounds loaded with (a) in-situ generated alkoxide silica and (b) commercial precipitated silica-filled compounds. The rubber matrix consists of solution styrene butadiene rubber polymers (SSBR). The in-situ generated particles are entirely different in filler morphology, i.e., in terms of size and physical structure, when compared to the precipitated silica. However, both types of the silicas were identified as amorphous in nature. Influence of filler morphology and surface modification of silica on the end performances of the rubbers like dynamic friction, abrasion index, and fatigue crack propagation were investigated. Compared to precipitated silica composites, in-situ derived silica composites offer better abrasion behavior and improved crack propagation with and without admixture of silane coupling agents. Silane modification, particle morphology, and crosslink density were identified as further vital parameters influencing the investigated rubber properties.

Graphene oxide/waterborne polyurethane nanocoatings: effects of graphene oxide content on performance properties

Graphene oxide (GO) is a good nanofiller candidate for waterborne coatings because of its outstanding physical and mechanical properties, good dispersibility in water, and low cost relative to graphene. Here, we report on the performance of a one-part, waterborne polyurethane (WPU) nanocoating formulated with four different GO loadings ([0.4% to 2.0%] by mass). The degree of GO dispersion/adhesion was evaluated using scanning electron microscopy, laser scanning confocal microscopy, and Raman microscopy. Nanocoating performance was evaluated using a dynamic mechanical thermal analyzer for mechanical properties, a customized coulometric permeation apparatus for oxygen barrier properties, a combustion microcalorimeter for flammability, a hot disk analyzer for thermal conductivity, thermogravimetric analysis for thermal stability, and a moisture sorption analyzer for water uptake. The results show that GO sheets were well dispersed in, and have good adhesion to, WPU. At the higher mass loadings ([1.2% or 2%] by mass), GO increased the modulus and yield strength of WPU by 300% and 200%, respectively, increased the thermal conductivity by 38%, reduced the burning heat release rate (flammability) by 43%, and reduced the oxygen permeability by up to sevenfold. The presence of GO, however, increased water vapor uptake at high humidity; the moisture content of 2% mass loading GO/WPU nanocoatings at 90% RH was almost twice that of the moisture content for unfilled WPU. Overall, with the exception of water uptake at very high humidity (> 70% RH), the observed improvements in physical and mechanical properties combined with the ease of processing suggest that GO is a viable nanofiller for WPU coatings.

Graphene quantum dot based materials for sensing, bio-imaging and energy storage applications: a review

Graphene quantum dots (GQDs) are an attractive nanomaterial consisting of a monolayer or a few layers of graphene having excellent and unique properties. GQDs are endowed with the properties of both carbon dots (CDs) and graphene. This review addresses applications of GQD based materials in sensing, bioimaging and energy storage. In the first part of the review, different approaches of GQD synthesis such as top-down and bottom-up synthesis methods have been discussed. The prime focus of this review is on green synthesis methods that have also been applied to the synthesis of GQDs. The GQDs have been discussed thoroughly for all the aspects along with their potential applications in sensors, biomedicine, and energy storage systems. In particular, emphasis is given to popular applications such as electrochemical and photoluminescence (PL) sensors, electrochemiluminescence (ECL) sensors, humidity and gas sensors, bioimaging, lithium-ion (Li-ion) batteries, supercapacitors and dye-sensitized solar cells. Finally, the challenges and the future perspectives of GQDs in the aforementioned application fields have been discussed.

Graphene quantum dots (GQDs) are an attractive nanomaterial consisting of a monolayer or a few layers of graphene having excellent and unique properties.

Highly Sensitive Piezoresistive Graphene-Based Stretchable Composites for Sensing Applications

Nanocarbonaceous materials with specific geometries and physicochemical properties allow the development of high-performance polymer-based smart composite materials. Among them, chemical treatments of graphene allow tailoring its electrical conductivity and, therefore, tuning functional response of materials for sensing applications. Polymer-based nanocomposites have been developed from styrene-ethylene-butylene-styrene (SEBS), a high deformation thermoplastic elastomer, and different graphene-based fillers, including graphene oxide (GO), reduced graphene oxide (rGO), and graphene nanoplatelets (G-NPLs). It is shown that the electrical conductivity shows a percolation threshold around 2 wt % for GO and rGO, remaining nearly independent of the filler content for G-NPL filler contents up to 6 wt %. Furthermore, GO/SEBS and rGO/SEBS composites show high piezoresistive sensibility with gauge factors ranging from 15 up to 120 for strains up to 10%. Thus, GO/SEBS and rGO/SEBS composites can represent a new generation of materials for strain sensor applications, as demonstrated in their implementation in a hand glove prototype with finger movement monitoring.

Molecular dynamics study of natural rubber-fullerene composites: connecting microscopic properties to macroscopic behavior

Macroscopic and microscopic properties of fullerene (C₆₀)-cis-polyisoprene (cis-PI) composites at varying fullerene concentrations were investigated using atomistic molecular dynamics (MD) simulations over microsecond time scales. Results show that the introduction of fullerenes into a polymer matrix increases density, bulk modulus and heat capacity while thermal expansivity decreases. The presence of fullerenes slowed the diffusion of both C₆₀ and cis-PI. Moreover, increasing fullerene concentration results in ordering of the cis-PI chains at the cis-PI-fullerene interfaces and shrinking of bulk PI regions. Free energy calculations of fullerene dimerization suggest that fullerenes disperse at low and aggregate at high fullerene concentrations. Our multi-scaled analysis approach demonstrates the role of 'ordered' regions adjacent to the interface between cis-PI and fullerene in controlling the level of order and mobility of the cis-PI chains. The relationship between the microscopic behavior and the changes in mechanical and thermal properties are discussed. Our study is beneficial for further studies and development of advanced rubber technology for novel, cost-effective, material with very high stiffness and thermal endurance with optimizing conditions of filler contents.

Synergistic Effect of Aligned Graphene Nanosheets in Graphene Foam for High-Performance Thermally Conductive Composites

Graphene shows a great potential for high-performance thermally conductive composite applications because of its extremely high thermal conductivity. However, the graphene-based polymer composites reported so far only have a limited thermal conductivity, with the highest thermal conductivity enhancement (TCE) per 1 vol% graphene less than 900%. Here, a continuous network of graphene foam (GF), filled with aligned graphene nanosheets (GNs), is shown to be an ideal filler structure for thermally conductive composite materials. Compared to previous reports, a clear thermal percolation is observed at a low graphene loading fraction. The GNs/GF/natural rubber composite shows the highest TCE of 8100% (6.2 vol% graphene loading) ever reported at room temperature, which gives a record-high TCE per 1 vol% graphene of 1300%. Further analyses reveal a significant synergistic effect between the aligned GNs and 3D interconnected GF, which plays a key role in the formation of a thermal percolation network to remarkably improve the thermal conductivity of the composites. Additionally, the use of this composite for efficient heat dissipation of light-emitting diode (LED) lamps is demonstrated. These findings provide valuable guidance to design high-performance graphene-based thermally conductive materials, and open up the possibility for the use of graphene in high-power electronic devices.

Carbonaceous Filler Type and Content Dependence of the Physical-Chemical and Electromechanical Properties of Thermoplastic Elastomer Polymer Composites

Graphene, carbon nanotubes (CNT), and carbon nanofibers (CNF) are the most studied nanocarbonaceous fillers for polymer-based composite fabrication due to their excellent overall properties. The combination of thermoplastic elastomers with excellent mechanical properties (e.g., styrene-b-(ethylene-co-butylene)-b-styrene (SEBS)) and conductive nanofillers such as those mentioned previously opens the way to the preparation of multifunctional materials for large-strain (up to 10% or even above) sensor applications. This work reports on the influence of different nanofillers (CNT, CNF, and graphene) on the properties of a SEBS matrix. It is shown that the overall properties of the composites depend on filler type and content, with special influence on the electrical properties. CNT/SEBS composites presented a percolation threshold near 1 wt.% filler content, whereas CNF and graphene-based composites showed a percolation threshold above 5 wt.%. Maximum strain remained similar for most filler types and contents, except for the largest filler contents (1 wt.% or more) in graphene (G)/SEBS composites, showing a reduction from 600% for SEBS to 150% for 5G/SEBS. Electromechanical properties of CNT/SEBS composite for strains up to 10% showed a gauge factor (GF) varying from 2 to 2.5 for different applied strains. The electrical conductivity of the G and CNF composites at up to 5 wt.% filler content was not suitable for the development of piezoresistive sensing materials. We performed thermal ageing at 120 °C for 1, 24, and 72 h for SEBS and its composites with 5 wt.% nanofiller content in order to evaluate the stability of the material properties for high-temperature applications. The mechanical, thermal, and chemical properties of SEBS and the composites were identical to those of pristine composites, but the electrical conductivity decreased by near one order of magnitude and the GF decreased to values between 0.5 and 1 in aged CNT/SEBS composites. Thus, the materials can still be used as large-deformation sensors, but the reduction of both electrical and electromechanical response has to be considered.

Synthesis, optimization and applications of ZnO/polymer nanocomposites

Polymer composites have established an excellent position among the technologically essential materials because of their wide range of applications. An enormous research interest has been devoted to zinc oxide (ZnO) based polymer nanocomposites, due to their exceptional electrical, optical, thermal, mechanical, catalytic, and biomedical properties. This article provides a review of various polymer composites consisting of ZnO nanoparticles (NPs) as reinforcements, exhibiting excellent properties for applications such as the dielectric, sensing, piezoelectric, electromagnetic shielding, thermal conductivity and energy storage. The preparation methods of such composites including solution blending, in situ polymerization, and melt intercalation are also explained. The current challenges and potential applications of these composites are provided in order to guide future progress on the development of more promising materials. Finally, a detailed summary of the current trends in the field is presented to progressively show the future prospects for the development of ZnO containing polymer nanocomposite materials.

Synergistic Effect on the Thermomechanical and Electrical Properties of Epoxy Composites with the Enhancement of Carbon Nanotubes and Graphene Nano Platelets

The synergetic effect of adding multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) on the thermomechanical properties and electric resistance of epoxy polymers were experimentally analyzed in this study. The total content of two employed carbon fillers were kept constant at 0.4 wt %, and seven filler ratios between two fillers (MWCNTs:GNPs), i.e., 10:0, 1:9, 3:7, 5:5, 7:3, 9:1, and 0:10, were considered in the experimental program to investigate the influences of employed nano-filler ratios on the viscoelastic and electrical properties of the studied nanocomposites. The thermomechanical properties and the sheet resistance of the nanocomposites were analyzed using a dynamic mechanical analyzer and four-point probe, respectively. Moreover, the thermogravimetric analyzer was utilized to measure the pyrolysis temperature of the nanocomposites. Experimental results show that the synergistic effect of adding two nano-fillers were clear for the improvement of the storage moduli, glass transition temperatures, and electric conductivity. Oppositely, the employment of two fillers has a slight effect on the pyrolysis temperatures of the studied nanocomposites. The composites with the MWCNT:GNP ratio of 1:9 display the most apparent enhancement of the thermomechanical properties. The improvement results from the uniform distribution and the high aspect ratio of GNPs. The addition of a small amount of MWCNTs provides more linkage in the matrix. Moreover, the specimens with the MWCNT:GNP ratio of 1:9 shows remarkable electrical properties, which result from the large contact surface areas of GNPs with each other. The employment of few MWCNTs plays an important bridging role between the layered GNPs.

Natural Rubber Nanocomposites: A Review

This paper reviews studies carried out on natural rubber filled with nanofillers such as spherical silica particles (generated by the sol gel reaction), clays and carbon nanostructures. It is shown that the mechanical response of NR is influenced by several parameters including the processing conditions, the state of filler dispersion, the polymer-filler interactions and the filler morphological aspects. Even if the sol gel process conducted in vulcanized rubber yields almost ideal dispersions, rod-shaped particles such as clay, carbon fibers or carbon nanotubes are by far more efficient in terms of mechanical reinforcement on account of their anisotropic character and their ability to orientate in the direction of stretch. The efficiency of layered fillers such as clays or graphitic structures clearly depends on the way they are dispersed (exfoliated) in the rubber. Complete exfoliation still remains difficult to achieve which limits the tremendous nanoreinforcement expected from a single layer of clay or graphite. In all cases, the onset of crystallization is observed at a lower strain value than that of the unfilled matrix due to strain amplification effects.