In this work, we demonstrate that a graphene oxide (GO) hydrogel with unique rheological properties, such as high storage modulus, shear-thinning nature and fast viscosity recovery, is highly suitable as an ink for three dimensional (3D) printing. The results show that the GO ink has the characteristics of both gel and viscous liquid, where the gel-liquid transition depends on the shear rate and shear strain amplitude. In the extrusion and printing process, the ink shows significant shear thinning and rapid viscosity recovery after cessation of shearing, which are desirable for 3D printing through direct ink writing (DIW). A suitable scanning speed and extrusion speed were determined to construct a precise 3D structure. After the reduction, the RGO electrode with hierarchical porous structures is stable, of higher precision, and loaded with more of the effective materials per unit area. The 3D printed micro-supercapacitors (MSCs) with interdigitated architecture exhibit a high areal specific capacitance of 101 mF cm À2 at a current density of 0.5 mA cm À2 and 111 mF cm À2 at a scan rate of 10 mV s À1 , which are superior compared with most of the reported MSCs of carbon-based materials. Fig. 1 (a) Schematic illustration of the fabrication process of 3DHG-MSCs, (b) structural decomposition diagram of 3DHG-MSCs, (c) optical image of the 3D interdigitated architecture composed of three-pair fingers with 5 printed layers, (d) optical microscopic image of 3DHG electrode.This journal is

Properly controlling the rheological properties of nanoparticle inks is crucial to their printability. Here, it is reported that colloidal gels containing a dynamic network of graphene oxide (GO) sheets can display unusual rheological properties after high‐rate shearing. When mixed with polyaniline nanofiber dispersions, the GO network not only facilitates the gelation process but also serves as an effective energy‐transmission network to allow fast structural recovery after the gel is deformed by high‐rate shearing. This extraordinary fast recovery phenomenon has made it possible to use the conventional air‐brush spray technique to print the gel with high‐throughput and high fidelity on nonplanar flexible surfaces. The as‐printed micro‐supercapacitors exhibit an areal capacitance 4–6 times higher than traditionally spray‐printed ones. This work highlights the hidden potential of 2D materials as functional yet highly efficient rheological enhancers to facilitate industrial processing of nanomaterial‐based devices.

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In this work, reduced graphene oxide was used as a material to fabricate a superhydrophobic lotus-leaf-like surface through soft-lithographic duplication.

In this work, formation of graphene oxide (GO) nanoscrolls in organic solvents was investigated upon dispersing GO nanosheets in organic solvents by sonication. It was found that, in some of the organic solvents, the single-layer GO sheets can effectively curl onto themselves to form the nanoscrolls that then sediment under gravity from the dispersion media. The sedimentation was monitored by UV−vis spectroscopy when the GO suspensions were left aside for different time periods after the sonication. The nanoscrolls were separated and characterized by transmission electron microscopy (TEM) and electron diffraction (ED). A typical solvent with such scroll-forming function is pyridine, where 82% of the GO sheets form the GO nanoscrolls and undergo the sedimentation. Scroll formation is also observed for N,N-dimethylformamide (DMF), methanol, ethanol, isopropyl alcohol, acetic acid, and isobutyric acid, but the yields vary with the solvents. The scrolls formed in pyridine suspension show the average length over 20 μm, interlayer spacing of 0.6 nm, and average diameters of 186 and 192 nm for the two types of the GO samples used here. The scrolls formed in the other solvents show different average lengths and diameters governed by the properties of the solvents. The average lengths of the formed scrolls reflect the tendency of the GO sheets to curl into scrolls in the solvents, while the average number of the included sheets per scroll depends on the sedimentation rate in the suspensions. The scrolling behavior and mechanism are rationalized and elucidated by considering dipole moment, ζ potential, and Hansen solubility parameters of the solvents. Based on the above understanding, the GO scrolls with controllable lengths and diameters can be efficiently fabricated by selecting a suitable solvent, and are expected for applications in hydrogen storage, gas sensing devices, actuators, lubrication materials, and others.