Properties Of Graphene Oxide Paper Research Articles

Ultra-stiff graphene oxide paper prepared by directed-flow vacuum filtration

Abstract Graphene oxide (GO) paper is an attracting structural material because of its high stiffness and light-weight. In order to exploit the high strength and stiffness of individual GO nanosheet into GO paper, the fabrication process must be optimized. In this study we fabricated ultra-stiff and strong GO paper by directed-flow vacuum filtration and compared its mechanical properties under different loading conditions. We also explored the effect of cross-linking with borax, thermal annealing and sonication to further enhance mechanical properties. The stiffest GO paper reported here has a tensile modulus of 109.9 GPa and a flexural modulus of 45.7 GPa. We also found that the flexural modulus of GO paper is significantly lower than the tensile modulus because of interlayer shearing, micro-buckling and delamination during flexural deformation. The properties of GO papers therefore need to be carefully selected for mechanical structures where flexion is the major deformation. This study provides significant insights about improving mechanical properties of GO paper and selecting GO paper for different loading conditions.

Enhanced mechanical property and flame resistance of graphene oxide nanocomposite paper modified with functionalized silica nanoparticles

Graphene oxide (GO) paper with outstanding integrated multiple functionalities (good mechanical performance, thermal stability and flame resistance, etc.) is strongly needed for numerous potential applications in cutting-edge fields. In this work, we report a facile and green process to fabricate GO-based nanocomposite papers via introducing functionalized silica (f-SiO2) nanoparticles. The results reveal that addition of f-SiO2 produces simultaneous improvements in mechanical strength, stiffness and flame resistance for GO paper. With incorporation of 10 wt% f-SiO2, the tensile strength, elastic modulus and toughness of the GO/f-SiO2 nanocomposite papers can be increased by about 51%, 317%, and 69%, respectively. Various characterizations disclose that hydrogen bonds and covalent interactions between GO sheets and f-SiO2 mainly contribute to the effective load transfer and energy dissipation between them, and thus leading to the improvements of mechanical properties. Based on the structural observation and analysis, the improved flame resistance of the GO/f-SiO2 papers should be attributed to the formation of rGO/SiO2 protective char, which are derived from the decomposition and redeposition of the grafted silane molecules and inorganic SiO2 and thermal reduction of GO into rGO. Our results suggest that the mechanical and thermal properties of GO papers can be tuned by introducing inorganic/organic f-SiO2, providing a new route for the rational designing and development of mechanically flexible and flame-retardant GO-based nanocomposite paper materials.

Graphene Oxide Papers Simultaneously Doped with Mg(2+) and Cl(-) for Exceptional Mechanical, Electrical, and Dielectric Properties.

This paper reports simultaneous modification of graphene oxide (GO) papers by functionalization with MgCl2. The Mg(2+) ions enhance both the interlayer cross-links and lateral bridging between the edges of adjacent GO sheets by forming Mg-O bonds. The improved load transfer between the GO sheets gives rise to a maximum of 200 and 400% increases in Young's modulus and tensile strength of GO papers. The intercalation of chlorine between the GO layers alters the properties of GO papers in two ways by forming ionic Cl(-) and covalent C-Cl bonds. The p-doping effect arising from Cl contributes to large enhancements in electrical conductivities of GO papers, with a remarkable 2500-fold surge in the through-thickness direction. The layered structure and the anisotropic electrical conductivities of reduced GO papers naturally create numerous nanocapacitors that lead to charge accumulation based on the Maxwell-Wagner (MW) polarization. The combined effect of much promoted dipolar polarizations due to Mg-O, C-Cl, and Cl(-) species results in an exceptionally high dielectric constant greater than 60 000 and a dielectric loss of 3 at 1 kHz by doping with 2 mM MgCl2. The excellent mechanical and electrical properties along with unique dielectric performance shown by the modified GO and rGO papers open new avenues for niche applications, such as electromagnetic interference shielding materials.

Functional Anodic and Cathodic Transition of Graphene Oxide using Lead Electrodes and Its Electrochemistry

The transition in the composition, electrical and fracture properties of graphene oxide paper (GO) in at the anode (aGO) and cathode (cGO) of lead /sulphuric acid boundary have been studied. Higher thermal stability and lower weight loss of aGO (34wt% at 800 °C) with XRD peak at 2ϴ = 10.5° showed the reduction of the ordinary GO paper (95wt% at 800 °C). The fractographs from the SEM showed that the cGO failed by ductile rupture of a higher degree than the ordinary GO paper, while that of the aGO was brittle cleavage. UV-Vis, Fourier Transform Infrared and X-ray Photoelectron Spectroscopies showed the changes in functional groups, via the interaction of graphene oxide functional groups with protons, adsorbed oxygen containing ions. Graphene/lead oxide based composite was achieved by covalent interactions. Non-covalent complexation of metal ions with slight reduction gave rise to stronger graphene oxide paper at the cathode. The electrical conductivity of aGO are 1.61 x 106 S/m and those of the cGO are 4.27 X 105 S/m. This foremost work is useful for further study of graphene oxide electrochemical reduction and metallic oxide functionalization for electrode materials in advanced lead-carbon batteries.

Thickness Dependence of the Mechanical Properties of Free‐Standing Graphene Oxide Papers

Graphene oxide (GO) papers are candidates for structural materials in modern technology due to their high specific strength and stiffness. The relationship between their mechanical properties and structure needs to be systematically investigated before they can be applied to the broad range fields where they have potential. Herein, the mechanical properties of GO papers with various thicknesses (0.5–100 μm) are investigated using bulge and tensile test methods; this includes the Young's modulus, fracture strength, fracture strain, and toughness. The Young's modulus, fracture strength, and toughness are found to decrease with increasing thickness, with the first two exhibiting differences by a factor of four. In contrast, the fracture strain slightly increases with thickness. Transmission electron, scanning electron, and atomic force microscopy indicate that the mechanical properties vary with thickness due to variations in the inner structure and surface morphology, such as crack formation and surface roughness. Thicker GO papers are weaker because they contain more voids that are produced during the fabrication process. Surface wrinkles and residual stress are found to result in increased fracture strain. Determination of this structure–property relationship provide improved guidelines for the use of GO‐based thin‐film materials in mechanical structures.

Tensile and tearing fracture properties of graphene oxide papers intercalated with carbon nanotubes

The fracture behaviors of graphene oxide (GO) and GO/multi-walled carbon nanotube (MWCNT) hybrid papers are studied in both quasi-static mode-I opening and mode-III tearing fracture. Large GO papers give rise to a higher energy release rate and tearing toughness than those made from small GO sheets: about 36% and 70% enhancements are shown for the large GO papers due to a more compact structure and better GO sheet alignment. Hybridization of GO papers with MWCNTs also improves these properties when up to 5 wt.% of MWCNTs is incorporated, attributed to the stronger GO interlayer bonds through π–π interactions with intercalated MWCNTs. Fracture surface examination indicates that cleavage failure prevails in mode-I fracture depending on the size of GO sheets: the unsorted and large GO papers fail mainly by brittle cleavage of GO sheets whereas small GO papers fail by combined brittle cleavage and minor pullout following debonding of GO bundles. In contrast, combination of cleavage and debonding failures is dominant in mode-III fracture of GO papers, regardless of GO size. The torn edges present typical characteristics of a saw-tooth wave with disordered oscillation where the large GO papers exhibit generally higher amplitude peaks than the small GO papers.

Simultaneous enhancement of mechanical, electrical and thermal properties of graphene oxide paper by embedding dopamine

Reduced graphene oxide paper was fabricated by incorporating dopamine. By using adhesive property, reducing ability, high thermal stability, and high carbon-yielding characteristic of dopamine, the dopamine-embedded graphene oxide paper can be mechanically stronger, thermally more stable, and electrically more conductive compared to conventional graphene oxide paper. Herein, in order to preserve a planar structure of graphene sheets and obtain free-standing paper, a simple one-step fabrication method was introduced, in which vacuum-assisted filtration of a graphene oxide suspension and polymerization of dopamine proceed at the same time. The manufactured paper had sequentially layer-stacked and planar structure of graphene sheets and polydopamine. The paper showed increased tensile strength and elongation, and higher thermal stability. Electrical conductivity was recovered, which was not measurable in conventional graphene oxide paper. To investigate enhancement of reduction, thermal annealing was further carried out. As a result, a critical reduction temperature was lowered and higher electrical conductivity was recorded at all annealing temperatures.

Hierarchical Structure and Properties of Graphene Oxide Papers

The mechanical properties of graphene oxide papers have attracted significant attention in recent years due to their high stiffness and tough behavior. While the structural feature most commonly characterized is the nanosheet spacing, there is a hierarchical structure, which is likely responsible for the impressive mechanical properties. In this paper, we examine the structure of graphene oxide papers on several length scales using novel techniques to distinguish between lamellae and a newly defined feature, termed “super-lamellae.” The differentiation between these intermediate features provides context to the previously observed mechanical response and fracture surfaces of graphene oxide papers, particularly under uniaxial tension.

Temperature-dependent electrical property transition of graphene oxide paper

Reduction of graphene oxide is primarily important because different reduction methods may result in graphene with totally different properties. For systematically exploring the reduction of graphene oxide, studies of the temperature-dependent electrical properties of graphene oxide (GO) are urgently required. In this work, for the first time, broadband dielectric spectroscopy was used to carry out an in situ investigation on the transition of the electrical properties of GO paper from −40 to 150 °C. The results clearly reveal a very interesting four-stage transition of electrical properties of GO paper with increasing temperature: insulator below 10 °C (stage 1), semiconductor at between 10 and 90 °C (stage 2), insulator at between 90 and 100 °C (stage 3), and semiconductor again at above 100 °C (stage 4). Subsequently, the transition mechanism was discussed in combination with detailed dielectric properties, microstructure and thermogravimetric analyses. It is suggested that the temperature-dependent transition of electronic properties of GO is closely associated with the ion mobility, water molecules removal and the reduction of GO in the GO paper. Most importantly, the present work clearly demonstrates the reduction of GO paper starts at above 100 °C.

Tuning the Mechanical Properties of Graphene Oxide Paper and Its Associated Polymer Nanocomposites by Controlling Cooperative Intersheet Hydrogen Bonding

The mechanical properties of pristine graphene oxide paper and paper-like films of polyvinyl alcohol (PVA)-graphene oxide nanocomposite are investigated in a joint experimental-theoretical and computational study. In combination, these studies reveal a delicate relationship between the stiffness of these papers and the water content in their lamellar structures. ReaxFF-based molecular dynamics (MD) simulations elucidate the role of water molecules in modifying the mechanical properties of both pristine and nanocomposite graphene oxide papers, as bridge-forming water molecules between adjacent layers in the paper structure enhance stress transfer by means of a cooperative hydrogen-bonding network. For graphene oxide paper at an optimal concentration of ~5 wt % water, the degree of cooperative hydrogen bonding within the network comprising adjacent nanosheets and water molecules was found to optimally enhance the modulus of the paper without saturating the gallery space. Introducing PVA chains into the gallery space further enhances the cooperativity of this hydrogen-bonding network, in a manner similar to that found in natural biomaterials, resulting in increased stiffness of the composite. No optimal water concentration could be found for the PVA-graphene oxide nanocomposite papers, as dehydration of these structures continually enhances stiffness until a final water content of ~7 wt % (additional water cannot be removed from the system even after 12 h of annealing).

Exceptional negative thermal expansion and viscoelastic properties of graphene oxide paper

We report unusual negative thermal expansion and viscoelastic properties in graphene oxide paper. The paper was prepared from aqueous GO dispersions using a simple vacuum evaporation technique. From room temperature to 150°C, this paper-like graphene oxide sheet exhibits a constant negative thermal expansion coefficient of −67×10−6/°C along the in-plane direction. Peculiar hysteresis loops of thermal expansion-temperature curves are observed, which are affected by the cooling rate and starting temperature of cooling. The tensile tests on GO paper show clear hysteresis loops, revealing the viscoelastic property of the paper. The viscoelastic properties show excellent frequency-stability in the range of 1.0–60Hz. In the low temperature range −150 to 25°C, however, they show a strong temperature dependence. The storage modulus of the graphene oxide paper continuously increases with decreasing temperature.

Bioinspired approaches for optimizing the strength and toughness of graphene-based polymer nanocomposites

The exceptional mechanical properties of graphene have revealed appealing potential in developing lightweight, mechanically robust polymer materials. However, how to effectively balance their strength and toughness remains a challenge so far. Although only weak or brittle constituents can be utilized, nature exhibits a miraculous capacity for creating biological composites that can meet a variety of functional needs, which has stimulated one's strong interest in the design and manufacture of novel polymer nanocomposites. This highlight article briefly describes the advances of bioinspired approaches in improving the mechanical properties of graphene-based nanocomposites, involving three selected aspects, i.e., structure and mechanical properties of graphene oxide papers, construction of novel graphene–polymer interphases and synergistic mechanical improvements in graphene-based nanocomposites. It is emphasized that the hierarchical structure and interplay between different toughening mechanisms play crucial roles in the development of strong, tough graphene–polymer nanocomposites.