Graphene Polymer Research Articles

Large-area preparation of defect-repaired fluorocarbon polymer coatings on graphene for long-term corrosion resistance

The corrosion-resistant hybrid films based on fluorocarbon polymer and single layer graphene were prepared. The hydrophobic fluorocarbon film covered the defect on graphene coated Cu, which inhibited the direct corrosion at the defect site, and forbade the galvanic corrosion between graphene and Cu substrate. The results confirmed that the hybrid coatings showed much better anti-corrosion performance. Electrochemical impedance spectroscopy measurements revealed that the hybrid coatings provided an effective physical barrier against the corrosive medium. The finding here is critical in designing hybrid protective coatings with the defect-repaired structure on the graphene coated Cu.

Covalently grafting of self-assembled functionalized graphene oxide multilayer films on Si substrate for solid film lubrication

Graphene-based polymer brush containing multilayer film has been fabricated on silicon wafer (SW) via self-assembled multistep approach based on covalent insertion of 3-aminopropyltrimethoxysilane as a chemical linker on graphene oxide (GO) followed by covalently anchored with polyethyleneimine (PEI). A multilayer polymer brush film was then constructed by electrostatic layer-by-layer (LBL) self-assembly technique between positively charged outer layer PEI grafted GO and anionic polyelectrolyte, poly (sodium 4-styrenesulfonate) (PSS). The LBL formation and microstructure of as prepared films were characterized by Raman spectroscopy, atomic force microscopy, field emission scanning electron microscopy and elemental electron dispersive spectroscopy analysis. The changes in wettability of films during grafting of chemical components on silicon substrate were determined by water contact angle measurement. Microtribological performances of the films were investigated using ball-on-disc contact geometry in ambient condition. The influence of contact pressure and sliding velocity were also studied under reciprocating tribo contact to evaluate the load bearing ability of the films. The multilayer films exhibited low (~0.15–0.17) and steady coefficient of friction (COF) at 1 N load (contact pressure ~ 0.54 GPa) compared to bare SW (~0.6) with remarkable wear-resistivity. With increasing contact pressure (4 N, ~0.86 GPa), the multilayer films provided minimal COF and low wear depth with improved sliding durability among the films. The improved friction and wear resistivity of the multi-layer films are attributed to densely packed polymeric graphene lamella contributing low-resistance to shear during sliding and the presence of sulphur on PSS might assists in superior adhesion of delaminated film to steel counterface ball during shearing, which was investigated by microscopic and Raman spectral analysis.

Epitaxial Grown Ferroelectric Polymers on Graphene Layer for Non-Volatile Transistor Memory with Graphene Channel

Controlling the crystal orientation is important to ferroelectric polymers to enhance ferroelectric properties. Here, we demonstrated non-volatile ferroelectric polymer memory with exfoliated monolayer graphene and epitaxial grown ferroelectric polymer. The mechanically exfoliated and transferred graphene was used as channel and epitaxial substrate for poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE). The epitaxial interaction between graphene and ferroelectric polymer results aligned chain-axis of polymer along the graphene’s 3-fold symmetry and provide improved remnant polarization and coercive field. Furthermore, the epitaxial grown ferroelectric polymer and monolayer graphene with Cr/Au source and drain electrode and few layer graphene for gate electrode demonstrated non-volatile graphene transistor memory with retention and endurance cycles more than 10,000 sec and 1,000 times, respectively.

(Invited) Nano Carbon and Polymeric Materials for Energy Conversion and Storage

Green energy technologies have been highly demanded for a sustainable development. In this talk, our recent studies for the electricity conversion/storage using nano carbon and polymeric materials will be presented. These will include the material design, synthesis, and device fabrication, targeting for high energy efficiency and understanding the mechanism using simpler or cheap materials. Recent five references: "Polymeric Graphene Bulk Materials with a 3D Cross-Linked Monolithic Graphene Network", Wangqiao Chen, Peishuang Xiao, Honghui Chen, Hongtao Zhang, Qichun Zhang, and Yongsheng Chen*, Mater ., 2018, 1802403."Nonfullerene Tandem Organic Solar Cells with High Performance of 14.11%", Lingxian Meng, Yamin Zhang, Xiangjian Wan*, Chenxi Li, Xin Zhang, Yanbo Wang, Xin Ke, Zuo Xiao, Liming Ding*, Ruoxi Xia, Hin-Lap Yip, Yong Cao, Yongsheng Chen*, Science , 2018, 361, 1094-1098."Monolithic 3D Cross-linked Polymeric Graphene Materials and the Likes: Preparation and Their Redox Catalytic Applications",Yanhong Lu, Yanfeng Ma, Tengfei Zhang, Yang Yang, Lei Wei, and Yongsheng Chen , Am. Chem. Soc., 2018, 140 (37), pp 11538–11550."Ultra-Broadband Wide-Angle Terahertz Absorption Properties of 3D Graphene Foam",Zhiyu Huang, Honghui Chen, Yi Huang,* Zhen Ge, Ying Zhou, Yang Yang, Peishuang Xiao, Jiajie Liang, Tengfei Zhang, Qian Shi, Guanghao Li, and Yongsheng Chen, Funct. Mater. , 2017, 1704363“Macroscale light propulsion of 3D cross-linked graphene ”, Tengfei Zhang†, Huicong Chang†, Yingpeng Wu†, Peishuang Xiao, Ningbo Yi, Yanhong Lu, Yanfeng Ma, Yi Huang, Kai Zhao, Xiaoqing Yan, Zhibo Liu, Jianguo Tian and Yongsheng Chen*, Nature Photon., 2015, 9, 471-476

Elastic Modulus of Nanofiller in Polymer-Matrix Composites

The paper explores the stiffness of the nanofiller particle aggregates in polymer matrix composites, such as particulate reinforced, carbon nanotube polymer and graphene polymer composites, i.e. composites reinforced with 0D, 1D and 2D nanofillers. It is shown that independently of the nanofiller, the structure of its particle aggregates is characterized by the fractal dimension as a physically accurate parameter. The true elastic modulus of the nanofiller particle aggregates is determined by two factors, namely the aggregates structure and the stiffness of the polymer matrix. The idea about the reinforcement degree control of polymer-matrix composites by the nanofiller structure is proved in this paper.

Highly sensitive natural rubber/pristine graphene strain sensor prepared by a simple method

Uniform dispersion of pristine graphene in polymers has always been a difficulty in the research and industry. In this paper, a simple but effective method was used to uniformly disperse the pristine graphene in NR matrix to prepare an NR/pristine graphene composite. The conductivity of this composite with 5 wt% graphene loading fraction was ∼0.005 S/m, around 4 orders of magnitude higher than that prepared by other methods with a similar loading fraction. The gauge factor (GF) of the strain sensor using the as-prepared composite as the component could be as high as 46, taking a lead positon in the reported strain sensors. Owing to the high sensibility, the sensor was suitable to be used for the detection of very subtle motions such as breathing or heartbeat. In a wrist-pulse testing, premature beats, less forceful heartbeats, and the “P”“T”“D″ waves of the heartbeats could be precisely monitored and distinguished. Swallowing and vocalization could also be efficiently detected by attaching the sensor on the subject's throat.

Adsorption of CO2 gas on graphene–polymer composites

Three-dimensional graphene-polymer porous materials have been proposed recently as potential adsorbents for carbon dioxide capture. We report results from molecular dynamics simulations on the adsorption of CO2 gas by composite systems formed by six different types of polymers. All composites are characterized by a constant polymer-to-graphene mass-ratio of 1.02 and their capture capacity as a function of the gas pressure is analyzed relative to the adsorption of nitrogen and methane. The results were then compared to the performance obtained from a bare-graphene sheet. More specifically, we examined the abilities of hydrogen-bond donor groups, amines and amides, as well as aromatic rings to promote and discriminate CO2 capture. We find that bare-graphene displays the highest capacity to adsorb CO2. Nevertheless, increasing the number of amine/amide protic groups of the polymer augments the adsorption. In fact, the best performing polymer in our study, which contains three protic groups per monomer, exhibits capture of CO2 almost as good as bare-graphene. Furthermore, these protic polymers form substantial intra-polymer hydrogen bonds and consequently exhibit cohesive behavior. In these cases, the aggregation of the polymer resulted in partial exposure of the graphene sheet on which the gas can adsorb as well. In contrast aprotic polymers, such as poly(styrene) or poly(methyl-methacrylate), spread extensively on graphene and are characterized by small capacities to adsorb CO2. For all systems studied, CO2 is adsorbed preferentially relative to N2 and CH4. This preferential adsorption is almost constant as a function of the gas pressure with values ranging from 2 to 12.

Terahertz tunable photonic crystal optical filter containing graphene and nonlinear electro-optic polymer

In this paper, new photonic crystal optical filters with very unique optical characteristics are presented. The designed structures are composed of stacked SiO2 isotropic dielectric slabs separated by monolayer graphene sheets. Defect layers of nonlinear electro-optical polymer materials are also inserted to behave as the resonant areas. Results obtained by using the transfer matrix method approach clearly reflect the possibility of the wide photonic band gap generation in the absorption spectra of the proposed crystals in the terahertz frequency range. Furthermore, a very strong relation is seen between the defect layer(s) induced resonant modes and the location/number of the defect(s) inside the crystal. To widen the scope of our findings, in addition to studying the dependencies on the structural characteristics, the tunability of the optical features using the external parameters is investigated systematically. It is shown that the number and central frequencies of the resonant modes are controllable in the far-infrared range by adjusting the temperature and wave incident angle. Thus, the proposed crystals might have remarkable applications in the fabrication of multi-channel tunable filters used in optical integrated circuits.

Wrapping Liquids, Solids, and Gases in Thin Sheets

Many objects in nature and industry are wrapped in a thin sheet to enhance their chemical, mechanical, or optical properties. Similarly, there are a variety of methods for wrapping, from pressing a film onto a hard substrate to inflating a closed membrane, to spontaneously wrapping droplets using capillary forces. Each of these settings raises challenging nonlinear problems involving the geometry and mechanics of a thin sheet, often in the context of resolving a geometric incompatibility between two surfaces. Here, we review recent progress in this area, focusing on highly bendable films that are nonetheless hard to stretch, a class of materials that includes polymer films, metal foils, textiles, and graphene, as well as some biological materials. Significant attention is paid to two recent advances: a novel isometry that arises in the doubly-asymptotic limit of high flexibility and weak tensile forcing, and a simple geometric model for predicting the overall shape of an interfacial film while ignoring small-scale wrinkles, crumples, and folds.

Thermal bridging of graphene nanosheets via covalent molecular junctions: A non-equilibrium Green’s functions–density functional tight-binding study

Despite the uniquely high thermal conductivity of graphene is well known, the exploitation of graphene into thermally conductive nanomaterials and devices is limited by the inefficiency of thermal contacts between the individual nanosheets. A fascinating yet experimentally challenging route to enhance thermal conductance at contacts between graphene nanosheets is through molecular junctions, allowing covalently connecting nanosheets otherwise interacting only via weak Van der Waals forces. Beside the bare existence of covalent connections, the choice of molecular structures to be used as thermal junctions should be guided by their vibrational properties, in terms of phonon transfer through the molecular junction. In this paper, density functional tight-binding combined with Green functions formalism was applied for the calculation of thermal conductance and phonon spectra of several different aliphatic and aromatic molecular junctions between graphene nanosheets. Effect of molecular junction length, conformation, and aromaticity were studied in detail and correlated with phonon tunnelling spectra. The theoretical insight provided by this work can guide future experimental studies to select suitable molecular junctions in order to enhance the thermal transport by suppressing the interfacial thermal resistances, particularly attractive for various systems, including graphene nanopapers and graphene polymer nanocomposites, as well as related devices. In a broader view, the possibility to design molecular junctions to control phonon transport currently appears as an efficient way to produce phononic devices and controlling heat management in nanostructures.

Effect of reduction methods and functionalization on the dispersion of graphene in epoxy

Poor dispersion between graphene nanofiller and polymer matrix would limit the development and application of the polymeric composites. In our study, three reduction methods, chemical reduction using hydrazine hydrate (N2H4·H2O), high temperature, and solvothermal methods were used to reduce graphene oxide; then reduced graphene oxide (RGO) were further functionalized by sodium dodecyl benzene sulfonate (SDBS) and cetylpyridinium chloride (CPC). The functionalized RGO (FRGO) was characterized with Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, respectively. Subsequently, the studied RGO was incorporated into epoxy resin to fabricate composites. Hansen solubility parameters (HSPs) theory was used to predict dispersion of studied RGO in epoxy resin. The compatibility of different RGO with epoxy was calculated by HSPs and compared with the real dispersion of RGO and FRGO in epoxy resin, which was explored through light optional microscopy (LOM). The results indicated that the dispersion of studied RGO in epoxy predicted by HSPs theory is in a good agreement with the experimental results.

Electrospinning of Polystyrene/Polyhydroxybutyrate Nanofibers Doped with Porphyrin and Graphene for Chemiresistor Gas Sensors.

Structural and functional properties of polymer composites based on carbon nanomaterials are so attractive that they have become a big challenge in chemical sensors investigation. In the present study, a thin nanofibrous layer, comprising two insulating polymers (polystyrene (PS) and polyhydroxibutyrate (PHB)), a known percentage of nanofillers of mesoporous graphitized carbon (MGC) and a free-base tetraphenylporphyrin, was deposited onto an Interdigitated Electrode (IDE) by electrospinning technology. The potentials of the working temperature to drive both the sensitivity and the selectivity of the chemical sensor were studied and described. The effects of the porphyrin combination with the composite graphene–polymer system appeared evident when nanofibrous layers, with and without porphyrin, were compared for their morphology and electrical and sensing parameters. Porphyrin fibers appeared smoother and thinner and were more resistive at lower temperature, but became much more conductive when temperature increased to 60–70 °C. Both adsorption and diffusion of chemicals seemed ruled by porphyrin according its combination inside the composite fiber, since the response rates dramatically increased (toluene and acetic acid). Finally, the opposite effect of the working temperature on the sensitivity of the porphyrin-doped fibers (i.e., increasing) and the porphyrin-free fibers (i.e., decreasing) seemed further confirmation of the key role of such a macromolecule in the VOC (volatile organic compound) adsorption.

Electrical and rheological percolation threshold of graphene pastes for screen-printing

Purpose A comparison of electric and viscosity percolation threshold is crucial from the scientific and technical points of view to understand the features and capabilities of heterogeneous graphene composite materials and properly select the functional phase volume. Therefore, the purpose of this paper is to present the analysis of the electrical and rheological percolation thresholds in the polymer–graphene screen printing pastes and the analysis of the relation between these two parameters. Design/methodology/approach In the paper, the properties of polymer-based pastes with graphene nanoplatelets were tested: paste viscosity and printed layers conductivity. The tests of pastes with different filler content allowed to determine both the electrical and rheological percolation thresholds using power law, according to Kirkpatrick’s percolation model. Findings The electrical percolation threshold for graphene nanoplatelets (GNPs) in the composite was 0.74 Vol.% when the rheological percolation threshold is observed to be at 1.00 Vol.% of nanoplatelets. The percolation threshold values calculated using the Kirkpatrick’s percolation model were 0.87 and 0.5 Vol.% of GNPs in the paste for electrical and rheological percolation thresholds, respectively. Originality/value Recently, GNPs are becoming more popular as the material of the functional phase in screen printing heterophase materials, because of their unique mechanical and electrical properties. However, till date no research presented in the literature is related to the direct comparison of both the electrical and rheological percolation thresholds. Such analysis is important for the optimization of the printing process toward the highest quality of printed conductive paths, and finally the best electrical properties.

Tailoring graphene reinforced thermoset and biothermoset composites

Abstract The surge of knowledge among researchers pertaining to the excellent properties of graphene has led to the utilisation of graphene as a reinforced filler in polymer composites. Different methods of graphene preparation, either bottom-up or top-down methods, are important requirements of starting materials in producing reinforced properties in the composites. The starting graphene material produced is either further functionalised or directly used as a filler in thermoset polymer matrixes. An effective interaction between graphene and polymer matrixes is important and can be achieved by incorporating graphene into a thermoset polymer matrix through melt mixing, solution mixing or in situ polymerisation processes. In addition, by taking into consideration the importance of green and sustainable composites, the details of previous work on graphene reinforced bio-thermoset polymer matrixes is discussed. The resultant mechanical and thermal properties of the composites were associated to the chemical interaction between the graphene filler and a thermoset matrix. Exploration for further variations of graphene polymer composites are discussed by taking the reinforcement properties in graphene composite as a starting point.

Enhanced thermal properties of PDMS composites containing vertically aligned graphene tubes

The development of high-power electronics, such as Li-ion batteries for electric cars, demands effective thermal management, because the temperature rise beyond the normal operating range is detrimental to the electronic performance. Due to its high thermal conductivity, graphene would be one of the ideal candidates for thermal management. But in graphene/polymer composites, thermal energy takes far more time to transfer through polymer chains than through graphene due to the vibration of polymer chains and phonon scattering. In this work, vertically aligned graphene tubes /polydimethylsiloxane (PDMS) composites were prepared and their thermal properties were characterized. Graphene loadings were controlled from 1.09 wt% to 4.5 wt% in the composites. The ordered-orientation of graphene in polymer facilitates the heat transfer. The results show that the thermal conductivity reaches 1.7 W m-1 K−1, which is 10.8 times higher than that of pure PDMS. Incorporation of structured graphene can reduce the thermal expansion. It is forecasted that the prepared composites have considerable prospects in encapsulation and heat dissipation of electronic devices.

Study on dispersion of reduced graphene oxide on physical performance of Polyvinylidene fluoride composites by Hansen solubility parameters

Poor dispersion of graphene in solvents and polymers remains a critical obstacle in practical application of poly(vinylidene fluoride) (PVDF) composite which loading graphene as filler. In order to inhibit the aggregation of reduced graphene oxide (RGO), two dispersants, polyimide (PI) and polyaniline (PANI), were used to modify RGO via in situ polymerization. The functionalization of reduced graphene oxide was characterized by Fourier transform infrared (FT-IR) and X-ray diffraction (XRD). Hansen solubility parameters (HSPs) theory was an effective way to investigate the compatibility of reduced graphene oxide in various solvents and polymers. Light optical microscope was employed to evaluate actual dispersion of functionalized RGO within the PVDF matrix. From the practical consideration, the dielectric and dynamic mechanical properties of PVDF and the composites were tested by dielectric impedance spectrometer and dynamic mechanical analysis (DMA), which illustrated the dispersion of reduced graphene oxide in poly(vinylidene fluoride) was closely related to physical performance of composites.

Graphene-Augmented Polymer Stabilization: Drastically Reduced and Temperature-Independent Threshold and Improved Contrast Liquid Crystal Device.

Polymers reinforced with nanofillers, especially graphene in recent times, have continued to attract attention to realize novel materials that are cheap and also have better properties. At a different level, encapsulating liquid crystals (LCs) in polymer networks not only adds mechanical strength, but could also result in device-based refractive index mismatch. Here, we describe a novel strategy combining the best of both these concepts to create graphene-incorporated polymer-stabilized LC (PSLC) devices. The presence of graphene associated with the virtual surface of the polymer network besides introducing distinct morphological changes to the polymer architecture as seen by electron microscopy brings out several advantages for the PSLC characteristics, which include 7-fold lowered critical voltage, its temperature invariance, and enhanced contrast ratio between field-off scattering/field-on transparent states. The results bring to fore the importance of working at very-dilute-concentration limits of the filler nanoparticles in augmenting the desired properties. These observations open up a new vista for polymer–graphene composites in the area of device engineering, including substrate-free smart windows.

Designing surface-enhanced Raman scattering (SERS) platforms beyond hotspot engineering: emerging opportunities in analyte manipulations and hybrid materials.

Surface-enhanced Raman scattering (SERS) is a molecule-specific spectroscopic technique with diverse applications in (bio)chemistry, clinical diagnosis and toxin sensing. While hotspot engineering has expedited SERS development, it is still challenging to detect molecules with no specific affinity to plasmonic surfaces. With the aim of improving detection performances, we venture beyond hotspot engineering in this tutorial review and focus on emerging material design strategies to capture and confine analytes near SERS-active surfaces as well as various promising hybrid SERS platforms. We outline five major approaches to enhance SERS performance: (1) enlarging Raman scattering cross-sections of non-resonant molecules via chemical coupling reactions; (2) targeted chemical capturing of analytes through surface-grafted agents to localize them on plasmonic surfaces; (3) physically confining liquid analytes on non-wetting SERS-active surfaces and (4) confining gaseous analytes using porous materials over SERS hotspots; (5) synergizing conventional metal-based SERS platforms with functional materials such as graphene, semiconducting materials, and piezoelectric polymers. These approaches can be integrated with engineered hotspots as a multifaceted strategy to further boost SERS sensitivities that are unachievable using hotspot engineering alone. Finally, we highlight current challenges in this research area and suggest new research directions towards efficient SERS designs critical for real-world applications.

Fluorescent polymer dots and graphene oxide based nanocomplexes for "off-on" detection of metalloproteinase-9.

Numerous studies have demonstrated that cancer-related matrix metalloproteinase-9 (MMP-9) is an ideal biomarker for cancer diagnosis. However, most MMP-9 detection methods are expensive and time-consuming, and more convenient and specific MMP-9 detection methods are needed both clinically and in research. In the present study, peptide-linked polymer dots were assembled onto a graphene oxide surface to construct a graphene oxide-peptide-polymer dot (GO-Pep-Pdot) nanocomplex for sensitive, rapid, and accurate detection of MMP-9. In the absence of MMP-9, the nanocomplex was in an "off" state, whereas in the presence of MMP-9, the nanocomplex was turned "on", resulting in the emission of a fluorescence signal that is linearly correlated with the MMP-9 concentration. The limit of detection of the nanocomplex was 3.75 ng mL-1, lower than most methods. This method was successfully verified by detecting MMP-9 in clinical serum samples of prostate cancer. The results suggest that this protease nanocomplex is generic and can be adopted to respond to other proteases by selecting specific peptides with suitable cleavage sites in clinics.

Chemically Binding Scaffolded Anodes with 3D Graphene Architectures Realizing Fast and Stable Lithium Storage.

Three-dimensional (3D) graphene has emerged as an ideal platform to hybridize with electrochemically active materials for improved performances. However, for lithium storage, current anodic guests often exist in the form of nanoparticles, physically attached to graphene hosts, and therefore tend to detach from graphene matrices and aggregate into large congeries, causing considerable capacity fading upon repeated cycling. Herein, we develop a facile double-network hydrogel-enabled methodology for chemically binding anodic scaffolds with 3D graphene architectures. Taking tin-based alloy anodes as an example, the double-network hydrogel, containing interpenetrated cyano-bridged coordination polymer hydrogel and graphene oxide hydrogel, is directly converted to a physical-intertwined and chemical-bonded Sn−Ni alloy scaffold and graphene architecture (Sn−Ni/G) dual framework. The unique dual framework structure, with remarkable structural stability and charge-transport capability, enables the Sn−Ni/G anode to exhibit long-term cyclic life (701 mA h g−1 after 200 cycles at 0.1 A g−1) and high rate performance (497 and 390 mA h g−1 at 1 and 2 A g−1, respectively). This work provides a new perspective towards chemically binding scaffolded low-cost electrode and electrocatalyst materials with 3D graphene architectures for boosting energy storage and conversion.