Graphene-based Composite Films Research Articles

Preparation of environmentally stable graphene circuits for flexible light-emitting diodes using patterned laser direct writing

Flexible technology incorporating materials and manufacturing processes has attracted the attention of researchers and commercial entities. The study showed that using a laser to reduce graphene oxide patterns from a graphene-based composite film was an effective method for creating highly conductive flexible circuits for light-emitting diodes. The composite of graphene oxides/polyimide (GO/PI) could be a precursor for a flexible reduced graphene circuit by optimizing the ratio of GO/PI to 50 wt% GO and adjusting the focus depth to 13 % and packed density to 10 using a low-powered semiconductor laser. The laser effectively reduced GO into graphene and removed the oxygen-containing groups, resulting in a significant increase in carbon content from 72.58 % (C/O ratio of ∼ 3.20) to 83.43 % (C/O ratio of ∼ 5.96). It achieved a low resistance of the circuit at 19.76 Ω/sq while maintaining the stable flexibility of the polymer matrix, enabling a substrate-integrated circuit without any packaging in the air for flexible electronic devices. The demonstrated flexible circuit for light-emitting diodes showed good reliability and flexibility, enduring bending at 60 degrees over 150 cycles in 30 min. This versatile technique provided an innovating method for flexible graphene-based electronic circuits through digital patterned laser engraving in research and industrial applications.

Highly Thermoconductive, Strong Graphene-Based Composite Films by Eliminating Nanosheets Wrinkles

HighlightsHighly thermally conductive composite films with elimination of graphene nanosheet wrinkles prepared by a constrained drying strategy of in-plane stretching.Reveals the mechanism of graphene nanosheet wrinkle elimination to improve the thermal conductivity of composite films and demonstrates its use as a heat sink film for cooling flexible LED chips and smartphones.

Nanochannel regulation of graphene quantum dots composite membranes via electrospray assisted self-assembly method

Nanochannel construction and regulation of graphene-based composite films are critical to the efficient separation performance. We report on a novel approach to preparing porous graphene-based composite films based on electrospray assisted self-assembly method by intercalating diamine monomers between graphene quantum dots (GQDs) nanosheets. Four kinds of diamine monomers were chosen as the bridging agents to fine tune the nanochannels between GQDs nanosheets. The physicochemical structures of as-prepared GQDs composite membranes were further optimized by post-crosslinking. The results showed that the covalent reactions of GQDs nanosheets with diamine monomers were occurred simultaneously between parallel and perpendicular GQDs nanosheets in the membrane preparation process, which constructed the three-dimensional space architecture of the GQDs composite membrane. The diamine monomers with different structures and molecular weights could change the loose structures of the separation layers, which endowed the GQDs composite membranes with the adjustable pore size and better hydrophilicity, further affecting their dye desalination performance. With the increase of the molecular weight of diamine monomers, the pore size of GQDs composite membranes increased slightly from 3.4 nm (GQDs-EDA) to 3.8 nm (GQDs-PPD), while the dye rejection decreased slightly. This study provided an insight into the uniform self-assembly of GQDs into nanofilms to fine tune the nanochannel structure.

Facile construction of flexible multilayered graphene-based composite films for excellent electromagnetic interference shielding with ultralow-reflection

Precisely tailored green electromagnetic interference shielding materials with absorption-dominated ultrahigh shielding performance are highly desired, but they have been constantly challenged by the conflict between superb shielding efficiency, ultralow reflection loss, and low thickness. In this work, the compatibility of excellent shielding capability, imperceptible reflection, and low thickness is successfully achieved in a flexible graphene-based film by simply integrating out a foam-like graphene network on fabric skeleton (RGO@F) as a surface wave trapping layer of graphene film (GF). The composite films exhibit exceptional shielding performance of > 80 dB, minuscule reflection as low as 0.82 dB, and a thickness of merely 0.8 mm, which are superior to most literature reports and first achieved for film-based shields. The power coefficient of reflection (R) of RGO@F/GF is only 0.172, much lower than that of original GF (R > 0.992), manifesting the shielding mechanism of GF has been readily converted from reflection-dominated to absorption-dominated. Several proof-of-concept studies are given to demonstrate the broad generality of RGO@F to virtually any other reflection-dominated shielding material. This work represents a critical breakthrough in tailoring advanced green shielding materials and paves the way for facilely fabricating thin, absorption-dominated and ultra-strong performance shielding films from accessible common materials.

A flexible composite film electrode and supercapacitor based on combined effect between graphene oxide and graphene

Graphene film has drawn great attention in flexible supercapacitors for its large specific surface area and high conductivity, but the trade-off between capacitance (positively correlated with structural defects) and electrical conductivity (negatively correlated with structural defects) still hinder its application. Herein, a graphene-based composite film is fabricated by cooperating graphene oxide with highly conductive graphene flakes. With the combined effect, graphene flakes endow the composite films with high electrical conductivity, while graphene oxide provides extra pseudocapacitance. The composite film shows a high specific capacitance of 191.1 F g−1, which is far beyond that of pure graphene film (6.7 F g−1). The assembled flexible supercapacitor shows no capacitance decline when bent at different angles, and the capacitance retention of the supercapacitor keeps at 55.8% after 4500 bending-releasing cycles (0–180°). The excellent mechanical and electrochemical performance of reduced graphene oxide/graphene composite film makes it a promising candidate in flexible supercapacitors.

Ultrathin flexible electrospun carbon nanofibers reinforced graphene microgasbags films with three-dimensional conductive network toward synergetic enhanced electromagnetic interference shielding

In recent years, graphene-based composite films have been greatly developed in the field of electromagnetic shielding interference (EMI). However, it is still a huge challenge to prepare graphene-based composite films with excellent mechanical properties, conductivity and electromagnetic shielding properties. In this work, we adopted a facile and effective method by annealing the alkali-treated polyacrylonitrile (aPAN) nanofibers reinforced graphene oxide (GO) composite films at 2000 °C to obtain graphene-carbon nanofibers composite films (GCFs). Microscopically, carbon nanofibers (CNFs) were intercalated into the graphene sheets, and microgasbags structure was formed during the heat treatment process. The special structure makes GCFs have superior tensile strength (10.4 MPa) at 5% strain. After repeated folding over 1000 times, the films still demonstrate excellent structural integrity and flexibility performance. Interestingly, the graphene-based composite films with 10 wt% aPAN nanofibers exhibit an extremely low density of about 0.678 g/cm3 and excellent electrical conductivity of 1.72 × 105 S/m. Further, an outstanding electromagnetic shielding effectiveness (SE) of 55–57 dB was achieved, and the corresponding value of the specific SE/thickness can reach 67,601–70,059 dB·cm2/g, which is the highest among reported graphene-based shielding materials. The significant electromagnetic shielding performance is due to the synergistic enhancement effect brought by the excellent conductivity of carbon nanofibers and graphene, the formed effective conductive network and the microgasbags structure. Electromagnetism simulation further clarified that the underlying mechanism should be mainly attributed to the conduction loss and multiple reflections caused by the special structure of GCFs. This work will provide new solutions for low density, high flexibility and excellent electromagnetic shielding properties materials in the next generation of foldable and wearable electronics.

Bioproduced Polymers Self-Assemble with Graphene Oxide into Nanocomposite Films with Enhanced Mechanical Performance.

Graphene oxide (GO) has recently been highlighted as a promising multipurpose two-dimensional material. However, free-standing graphene oxide films suffer from poor strength and flexibility, which limits scaling-up of production and lifetime structural robustness in applications. Inspired by the relationship between the organic and inorganic components of the hierarchical structure of nacre found in mollusk shells, we have fabricated self-assembled, layered graphene-based composite films. The organic phase of our composite is produced via environmentally friendly and economical methods based on bacterial production of γ-poly(glutamic acid) (PGA). Composite films made of GO, PGA, and divalent cations (Ca2+) were prepared through a slow solvent evaporation method at ambient temperature, resulting in a nacre-like layered structure. These biobased nanocomposite films showed impressive mechanical properties, which resulted from a synergistic combination of hydrogen bonding with the bacterially produced PGA and ionic bonding with calcium ions (Ca2+). The GO/PGA/Ca2+ composite films possessed a high strength of 150 ± 51.9 MPa and a high Young’s modulus of 21.4 ± 8.7 GPa, which represents an increase of 120% and over 70% with respect to pure GO films. We provide rational design strategies for the production of graphene-based films with improved mechanical performance, which can be applied in filtration purification of wastewater in the paper, food, beverage, pigment, and pharmaceuticals industries, as well as for manufacturing of functional membranes and surface coatings.

Ultratough reduced graphene oxide composite films synergistically toughened and reinforced by polydopamine wrapped carbon nanotubes

Nacre like graphene based composite films (GCFs) have been developed over the last decade. Although the progress in ultrastrong GCFs is remarkable, fabricating GCFs with excellent integrated properties of strength, flexibility, and toughness still remains a challenge. Here, a ternary GCF of reduced graphene oxide (rGO), polydopamine (PDA) and multi-walled carbon nanotubes (MWCNTs) was developed. The MWCNTs were modified by PDA to form PDA@MWCNTs which were then compounded with GO to fabricate the rGO-PDA@MWCNT films by evaporation-induced assembly and chemical reduction. The preparation was simple, cheap and environmentally-friendly. The PDA increased the dispersion of MWCNTs in the rGO-PDA@MWCNT films, crosslinked the rGO sheets, and enhanced the entanglement of MWCNTs and the interactions between MWCNTs and rGO sheets. Benefiting from the synergistic effect of PDA and MWCNTs, the rGO-PDA@MWCNT films exhibited excellent integrated properties by increasing strength, tensile fracture strain and toughness to 579 ± 35 MPa, 12.03 ± 0.56%, and 34.03 ± 1.60 MJ/m3, which were 2.26, 2.02 and 4.94 times that of pure rGO films, respectively. The rGO-PDA@MWCNT films also exhibited a high conductivity of 612 ± 68 S/cm and excellent structural stability under extreme environments. These excellent integrated properties of the rGO-PDA@MWCNT films will promote their applications in aerospace engineering, flexible electrical devices and artificial muscle.

Assembly of carbon nanodots in graphene-based composite for flexible electro-thermal heater with ultrahigh efficiency

A high-efficiency electro-thermal heater requires simultaneously high electrical and thermal conductivities to generate and dissipate Joule heat efficiently. A low input voltage is essential to ensure the heater’s safe applications. However, the low voltage generally leads to low saturated temperature and heating rate and hence a low thermal efficiency. How to reduce the input voltage while maintaining a high electro-thermal efficiency is still a challenge. Herein, a highly electrical and thermal conductive film was constructed using a graphene-based composite which has an internal three-dimensional (3D) conductive network. In the 3D framework, cellulose nanocrystalline (CNC) phase with chiral liquid crystal manner presents in the form of aligned helix between the graphene oxide (GO) layers. Carbon nanodots (CDs) are assembled inside the composite as conductive nanofillers. Subsequent annealing and compression results in the formation of the assembled GO-CNC-CDs film. The carbonized CNC nanorods (CNR) with the helical alignment act as in-plane and through-plane connections of neighboring reduced GO (rGO) nanosheets, forming a conductive network in the composite film. The CDs with ultrafast electrons transfer rates provide additional electrons and phonons transport paths for the composite. As a result, the obtained graphene-based composite film (rGO-CNR-CDs) exhibited a high thermal conductivity of 1,978.6 W·m−1·K−1 and electrical conductivity of 2,053.4 S·cm−1, respectively. The composite film showed an outstanding electro-thermal heating efficiency with the saturated temperature of 315 °C and maximum heating rate of 44.9 °C·s−1 at a very low input voltage of 10 V. The freestanding graphene composite film with the delicate nanostructure design has a great potential to be integrated into electro-thermal devices.

Pulsed laser deposition of monolayer and bilayer graphene

The properties of graphene vary with the number of layers, thus determining its usefulness in different applications. Consequently, it is important to develop a method for precisely controlling the number of layers for various application demands. In this study, high quality monolayer graphene was successfully prepared using pulsed laser deposition. Meanwhile, the growth of monolayer and bilayer graphene can be controlled by adjusting the laser energy density. Raman spectra show that high quality monolayer films grew at a laser energy density of 5.66 J/cm2 and bilayer graphene films grew at a laser energy density of 8.49 J/cm2. X-ray photoelectron spectroscopy indicate that the main chemical state of carbon is the sp2 hybrid state, and the maximum atomic ratio of sp2 and sp3 results from the sample with laser energy density of 5.66 J/cm2. Scanning electron microscope images show that monolayer graphene is connected by small sheets with different sizes, and the largest graphene sheet reaches 20 μm. High resolution transmission electron microscope images and selected area electron diffraction patterns show that graphene samples are highly crystalline and yield significant layer information. UV–Vis spectra indicate that the transmittance through monolayer and bilayer graphene at 550 nm are 96.93% and 95.05%, respectively. Ultraviolet photoelectron spectroscopic measurements show that the work function of graphene ranges from 3.72 eV to 4.76 eV; the variation in the work function is related to growth defects. Finally, the relationship between the structure of the graphene films and laser energy density are investigated in detail, and these results indicate that the controllable growth of graphene can be achieved by adjusting the laser energy density. This means that a suitable laser energy density is conducive to defining an equilibrium between diffusion and condensation of carbon atoms, which is crucial to the growth of high-quality monolayer and bilayer graphene. It is expected that this study might be facilitate the preparation of graphene-based composite films and devices.

Synthesis and characterizations of graphene-based composite film for thermal dissipation

In this study, we develop a series of graphene nanosheets(GNs)/carbon nanotubes(CNTs)/copper(Cu) composite film for heat dissipation. Scanning electronic microscopy (SEM), Raman spectroscopy, X-ray photo spectroscopy (XPS), Laser flash and infrared thermal images of composite film are carried out in this study. We discovered that the content of CNTs in composite film plays an important role on heat dissipation performance. Optimized ratio of GNs to CNTs were found to be 6:4. Raman spectra showed that ID/IG ratio of GNs was 0.23, and the ID/IG ratio would increase to 0.84 by adding CNTs with the ratio of 6:4. Laser flash analysis shows that the thermal conductivity (K) could be enhanced from 520 W/m⋅K of GNs film to 687 W/m⋅K of GNs/CNTs composite film. Infrared thermal images also relative the relationship between the microstructure of composite film and heat dissipation performance. These data indicate that as-synthesized graphene nanosheets/CNTs/Cu composite film is a potential candidate for heat dissipation applications.

Coupled Chiral Structure in Graphene-Based Film for Ultrahigh Thermal Conductivity in Both In-Plane and Through-Plane Directions.

The development of high-performance thermal management materials to dissipate excessive heat both in plane and through plane is of special interest to maintain efficient operation and prolong the life of electronic devices. Herein, we designed and constructed a graphene-based composite film, which contains chiral liquid crystals (cellulose nanocrystals, CNCs) inside graphene oxide (GO). The composite film was prepared by annealing and compacting of self-assembled GO-CNC, which contains chiral smectic liquid crystal structures. The helical arranged nanorods of carbonized CNC act as in-plane connections, which bridge neighboring graphene sheets. More interestingly, the chiral structures also act as through-plane connections, which bridge the upper and lower graphene layers. As a result, the graphene-based composite film shows extraordinary thermal conductivity, in both in-plane (1820.4 W m-1 K-1) and through-plane (4.596 W m-1 K-1) directions. As a thermal management material, the heat dissipation and transportation behaviors of the composite film were investigated using a self-heating system and the results showed that the real-time temperature of the heater covered with the film was 44.5 °C lower than a naked heater. The prepared film shows a much higher efficiency of heat transportation than the commonly used thermal conductive Cu foil. Additionally, this graphene-based composite film exhibits excellent mechanical strength of 31.6 MPa and an electrical conductivity of 667.4 S cm-1. The strategy reported here may open a new avenue to the development of high-performance thermal management films.

Flexible Graphene-Based Composite Films for Supercapacitors with Tunable Areal Capacitance

Flexible supercapacitors based on paper-like electrodes have attracted significant interest because of the increasing demands in the energy storage, and they are recently claimed to be minimized and portable for meeting practical applications. As promising binder-free electrode materials in the supercapacitors, graphene-based films have been developed for enhancing their performance in energy storage by insetting “spacers” in-between nanosheets to prevent inevitable aggregations. In this study, a facile and versatile strategy is presented for fabricating graphene-based composite films by introducing activated carbonized cotton fibers to regulate the chemical composition, surface area and pore size distribution. The obtained composite films permit to present substantially increased energy storage capability (capacitance of 310Fg−1 and 150Fg−1 at 0.1Ag−1 and 10Ag−1 in 6molL−1 KOH electrolyte, respectively). Furthermore, tunable areal capacitance is realized by altering the stacked film layers without loss of mass specific capacitance. The devices based on composite films with excellent power density (up to 156.5mWcm−2) and energy density (240μWhcm−2) highlight a controllable, mini-sized and high-efficiency stage for energy storage. Such unique strategy suggests great potential in the commercialization of portable electronic devices, which require greater capacitance in a limited area.

Large-scale graphene-based composite films for flexible transparent electrodes fabricated by electrospray deposition

Large-scale transparent conducting electrodes were fabricated using the electrospray method on a glass wafer and polyethylene terephthalate film using chemically reduced graphene oxide and poly (3,4-ethylenedioxythiophene) (PEDOT). Graphene oxide (GO) is prepared by the modified Hummers method, and reduced GO (RG) is prepared at low temperature. By varying the concentration of RG and PEDOT of the composite material on the substrate, the electrical conductivity and transmittance of the electrode was controlled. The optical transmittance values of the graphene-based electrode at a wavelength of 550 nm were between 81 and 95% and had sheet resistances from 370 to 5400 Ω sq−1. After 1000 cycles of a bending test, the sheet resistances of the graphene-based composite films were unchanged. Different types of graphene and graphene-based electrodes were characterized by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, high-resolution Raman spectroscopy, x-ray photoelectron spectroscopy, x-ray diffraction, transmittance, and electrical conductivity measurements.

Flexible graphene/polymer composite films in sandwich structures for effective electromagnetic interference shielding

Multilayer graphene/polymer composite films with good mechanical flexibility were fabricated into paraffin-based sandwich structures to evaluate electromagnetic interference (EMI) shielding. Experimental results showed the relationship between electrical properties and shielding performance, demonstrating that electrical properties are significant factors in EMI shielding. Calculation based on electrical conductivity of the composite films was carried out to investigate the fundamental mechanisms of absorption, reflection and multiple-reflections for the polymeric graphene composite films. Both experimental and calculated results indicate that reflection is the dominating shielding mechanism for the as-fabricated polymeric graphene films. The optimization of thickness, skin depth and electrical conductivity in the shielding materials could be highly significant in achieving enhanced EMI shielding. Further improvement in absorption shielding has been achieved by increasing the shielding thickness in order to enhance the overall shielding performance. The optimized shielding effectiveness up to 27dB suggested effective shielding of the composite films. The implication of the mechanisms for optimizing shielding performance demonstrates significant fundamental basis for designing high-performance EMI shielding composites. The results and techniques also promise a simple and effective approach to achieve light-weight graphene-based composite films for application potentials in EMI shielding coatings.