An Active Vibration Isolation and Compensation System for Improving Optical Image Quality: Modeling and Experiment.

Optical detection equipment (ODE) is subjected to vibrations that hamper the quality of imaging. In this paper, an active vibration isolation and compensation system (VICS) for the ODE is developed and systematically studied to improve the optical imaging quality. An active vibration isolator for cameras is designed, employing a dual-loop control strategy with position compensation and integral force feedback (IFF) control, and establishing the mapping relationship between vibration and image quality. A performance metric for evaluating images is also proposed. Finally, an experimental platform is constructed to verify its effectiveness. Based on the experimental results, it can be concluded that the proposed VICS effectively isolates vibrations, resulting in a reduction of 13.95 dB in the peak at the natural frequency and an 11.76 Hz widening of the isolation bandwidth compared with the system without it. At the same time, the experiments demonstrate that the image performance metric value increases by 46.03% near the natural frequency.

High-compact MXene-based coatings by controllable interfacial structures.

Titanium carbide (Ti3C2Tx) MXenes have been regarded as important functional fillers of organic coatings for anticorrosion. Various MXene-based composite coatings have been fabricated and investigated via a material modification strategy, enhancing the corrosion protection performance. However, the anticorrosion reliabilities of MXene-based composite coatings were thwarted by their disordered interfaces. Significantly, few reports discuss the influence of interface structures on the protection performance for the coatings. In this work, we confirm the exceptional anticorrosion performance of ordered MXene/epoxy composite (OMC) coatings via a reasonable interface strategy. The ordered interfacial structure can synergistically enhance the coating compactness while maximizing the infiltration paths of aggressive species. The obtained OMC coating is compact and shows a high impedance of 6.84 × 109 Ohm cm2, a high coating resistance of 6.08 × 109 Ohm cm2, an extremely low porosity of 0.77% and an extremely low breakpoint frequency of 0.18 Hz, at a low filler content of 0.5 wt%. Besides, the concept of specific impedance (SZ) is proposed to attest the superiority of the OMC coating. Furthermore, the galvanic corrosion effects of MXenes in epoxy coatings are systematically explored and confirmed for the first time. The highly ordered structure eliminates the corrosion promotion activity of the conductive MXene, and thus, endows the superior anticorrosion stability for the coating. This work provides an inspiration for constructing outstanding long-term MXene-based anticorrosion coatings via regulating the coating interface.

A cantilever-structure triboelectric nanogenerator for energy harvesting and defect detection via long short-term memory network.

The electric signals of cantilever energy harvesting devices with/without a crack were mainly obtained by external sensors, so detecting device damage on a large scale is difficult. To tackle the issue, a cantilever-structure freestanding triboelectric nanogenerator (CSF-TENG) device was proposed, which can scavenge ambient energy and act as a self-powered sensor. Firstly, the relation between the peak-to-peak voltage and amplitude of the CSF-TENG was established. Next, the output performance of the CSF-TENG was measured. Then, depending on electric signals output by the CSF-TENG, a cantilever defect identification model was built by using the wavelet packet and long short-term memory (LSTM) algorithms. The experimental results manifest that the accuracy of the model is about 98.6%. Thus, the CSF-TENG with a crack can be detected timely due to its self-monitoring ability, which is of great significance for the development of self-powered sensor networks.

Bio-inspired Multifunctional Graphene-Epoxy Anticorrosion Coatings by Low-Defect Engineered Graphene.

Although graphene has been regarded as the most ideal anticorrosion filler, to date, some vital problems including poor dispersion, disordered arrangement, structure defects, and galvanic corrosion remain unresolved,, thus blocking its potential application in metal protection. In this work, a bio-inspried multilayered graphene-epoxy composite coating was fabricated through a scalable spraying approach with well-dispersed low-defect engineered graphene as the functional filler. Polydopamine served as an enforcer to improve the dispersity and repair the structure defects of graphene (π-π interaction) and bridged the dense graphene layers and epoxy layers (strong adhesion) for forming "interlock" structures to ensure complete coating systems. Electrochemical tests confirmed that the bio-inspired composite coating showed elevated coating resistance from 4.2 × 106 Ω cm2 for blank coating and 2.5 × 108 Ω cm2 for blending composite coating to 3.0 × 109 Ω cm2. The highly anisotropic graphene layers endowed the bio-inspried coating with highly anisotropic thermal and electrical conductivities, with the in-plane and through-plane thermal conductivities being 0.78 and 0.21 W/mK, respectively. Besides, the good anisotropic conductivities make the bio-inspired coating achieve self-monitoring of structural safety and health. This bio-inspired strategy provides a fascinating method for constructing high-performance graphene composite coatings with functional properties.

Correction: An ultrahigh thermal conductive graphene flexible paper.

Correction for 'An ultrahigh thermal conductive graphene flexible paper' by Jiheng Ding et al., Nanoscale, 2017, 9, 16871-16878, DOI: 10.1039/C7NR06667H.

Piezoelectric Energy Harvesting from Suspension Structures with Piezoelectric Layers.

In this paper, we propose a generator for piezoelectric energy harvesting from suspension structures. This device consists of a leaf spring and eight pairs of piezoelectric layers attached to inner and outer surfaces. We present a special type of leaf spring, which can magnify the force from the workload to allow the piezoelectric layers to achieve larger deformation. The generator is to solve the problem of vibration energy reutilization in a low-frequency vibration system. To verify the efficiency of the proposed configuration, a series of experiments are operated. The results indicate that the resonance frequency (25.2 Hz) obtained from the sweep experiment is close to the simulation result (26.1 Hz). Impedance-matching experiments show that the sum of the output power attains 1.7 mW, and the maximum single layer reaches 0.6 mW with an impedance matching of 610 KΩ, and the instantaneous peak-peak power density is 3.82 mW/cm3. The capacitor-charging performance of the generator is also excellent under the series condition. For a 4.7 µF capacitor, the voltage is charged to 25 V in 30 s and limited at 32 V in 80 s. These results demonstrate the exploitable potential of piezoelectric energy harvesting from suspension structures.

Superior to graphene: super-anticorrosive natural mica nanosheets.

Graphene has been generally considered to be the most ideal anticorrosive material based on its extraordinary impermeability, but tends in practical applications to promote metal corrosion because of its inherently high electrical conductivity. Mica nanosheets (MNSs), in contrast, display excellent electrical insulation properties, as well as excellent temperature stability and chemical durability, and show tremendous potential for protecting metals, and hence are a promising substitute for graphene. To date, however, there have been no reports about MNS-based anticorrosive coatings, since it is much more difficult to exfoliate high-quality MNSs than other layered materials. In this work, high-concentration (4.3 mg ml-1) ultrathin MNS (1-5 layers) dispersions were synthesized based on a facile and efficient hydrothermal exfoliation approach. Epoxy (EP) coatings were filled with the as-obtained MNSs to enhance the anticorrosion performance of the coatings, and their corrosion behaviors were studied systemically through a series of measurements. With the addition of only 0.4 wt% MNSs, the corrosion rate was observed to be reduced 6500 fold, and the coating impedance increased by four orders of magnitude compared with the blank EP coating. We believe that this method opens a novel avenue for developing high-performance anticorrosive coatings to replace graphene materials for metal protection.

Bioinspired Smart Anticorrosive Coatings with an Emergency-Response Closing Function.

Emergency-response closing (ERC) of diffusion pathways for aggressive species in graphene/epoxy (G/EP) coatings was achieved via terpyridine derivative (TDD)-functionalized graphene oxide (tGO). Under stimulation from corrosion produced ferrous (Fe2+) ions, tGO sheets urgently aggregated through complexation reminiscent of leaves closing on a mimosa. Consequently, the coating showed significantly decreased oxygen (ORT) and water vapor transmittance rate (WVTR) changes after immersion in ferrous solution. According to the simulation and electrochemical results, tGO sheets could self-assemble into 3D architectures with Fe2+ ions and efficiently protect metals from aggressive species attack. This tGO/EP coating provided an ERC function via self-adaptability with the Fe2+ ions to achieve long-term anticorrosion. The application of tGO/EP to the protection of metal components is therefore validated as a fascinating route for the enhancement of anticorrosion efficiency on graphene anticorrosive coatings, with great potential in durable anticorrosive coatings application.

High-Quality Boron Nitride Nanosheets and Their Bioinspired Thermally Conductive Papers.

Hexagonal boron nitride has displayed increased potential in heat dissipation applications due to its desirable high thermal conductivity and remarkable thermal stability. However, the large-yield and high-quality preparation of boron nitride nanosheets (BNNSs) has been still an enormous challenge. In present work, we developed a universal exfoliation strategy to synthesize few-layer and defect-free BNNSs, which involved the intercalation of hexafluorosilicates/sodium hydroxide into BN crystals followed by exfoliation through a mild stirring process. The yield and concentration of as-obtained BNNS reached up to 78.5% and 12.78 mg/mL, respectively. More importantly, this method has been proven to exfoliate other layered materials like graphene (G), MoS2, and WS2. These as-obtained BNNSs can be directly used for constructing freestanding papers with high thermal conductivities. Typically, the thermal conductivities of the BNNS-G hybrid paper were up to 63.5 W/mK along the in-plane direction and 7.4 W/mK along the through-plane direction. According to the thermal interface materials performance measures, BNNS-G hybrid paper shows great promising applications for heat transfer in integrated circuit packaging.

Ultrafast molecular sieving through functionalized graphene membranes.

Graphene shows great promise for advanced filtration membranes with high permeance and enhanced rejection. Here we demonstrate filtration membranes with a nanochannel network for superior separation performance using 100-500 nm-wide graphene nanoplatelets (GnPs) that are efficiently prepared via a green method. The resulting membranes exhibit a well packed layer structure formed by GnPs and are highly stable in water and organic solvents and even in strongly acidic and alkaline media. Moreover, the GnP membranes possess high fluxes and good selectivity in both water and organic solvents based on the small size nanoplatelets and the stable nanochannels between the GnPs. The exfoliated GnPs and the subsequent membranes show great potential for practical applications in water purification and organic solvent filtration.

Bio-based, biodegradable and amorphous polyurethanes with shape memory behavior at body temperature.

In this work, a series of bio-based, biodegradable and amorphous shape memory polyurethanes were synthesized by a two-step pre-polymerization process from polylactide (PLA) diol, polycaprolactone (PCL) diol and diphenylmethane diisocyanate-50 (MDI-50). The ratio of PLA diol to PCL diol was adjusted to investigate their thermal and mechanical properties. These bio-based shape memory polyurethanes (bio-PUs) showed a glass transition temperature (T g) value in the range of -10.7-32.5 °C, which can be adjusted to be close to body temperature. The tensile strength and elongation of the bio-PUs could be tuned in the range from 1.7 MPa to 12.9 MPa and from 767.5% to 1345.7%, respectively. Through a series of shape memory tests, these bio-PUs exhibited good shape memory behavior at body temperature. Among them, PU with 2 : 1 as the PLA/PCL ratio showed the best shape recovery behavior with a shape recovery rate higher than 98% and could fully reach the original shape state in 15 s at 37 °C. Therefore, these shape memory bio-PUs are promising for applications in smart biomedical devices.

Variation of mechanical and thermal properties in sustainable graphene oxide/epoxy composites.

In this work, the functional graphene oxide (bGO) was facilely synthesized through a grafted reaction between graphene oxide (GO) and bio-based bis-furan di-epoxide (BFDE). The structure of bGO was confirmed by FTIR spectra and Raman spectra. The properties of polymer composite materials depend on the distribution of the nanofiller in the matrix and due to the presence of polymer chains our bGO sheets exhibit a better dispersibility in solvents and polymer matrix, which provides a potential opportunity for the preparation of BFDE composites with excellent performance. Bio-based BFDE composites containing 0.05-0.5 wt.% of bGO exhibit superior mechanical and thermal properties. The addition of just 0.5 wt% such bGO to an BFDE causes 80%, 49%, 21%, 69% and 97% enhancement in tensile strength, flexural strength, flexural modulus, critical stress intensity factor and critical strain energy release rate, respectively. The thermal decomposition temperature Td of bGO/BFDE composites was increased about ~17 °C compared to blank BFDE sample. In addition, we found that introducing unmodified GO to epoxy matrix lead to an insignificant increase of the thermal property of the resulting GO/BFDE composites. The enhanced mechanical properties and thermal properties of bGO/BFDE composites could be attributed to strong interfacial interactions and high affinity between bGO and epoxy matrix.

A water-based green approach to large-scale production of aqueous compatible graphene nanoplatelets.

The unique properties of graphene are highly desired for printing electronics, coatings, energy storage, separation membranes, biomedicine, and composites. However, the high efficiency exfoliation of graphene into single- or few-layered nanoplates remains a grand challenge and becomes the bottleneck in essential studies and applications of graphene. Here, we report a scalable and green method to exfoliate graphene nanoplatelets (GNPs) from nature graphite in pure water without using any chemicals or surfactants. The essence of this strategy lies in the facile liquid exfoliation route with the assistance of vapor pretreatment for the preparation of edge hydroxylated graphene. The produced graphene consisted primarily of fewer than ten atomic layers. Such the water soluble graphene can be stored in the form of dispersion (~0.55 g L-1) or filter cake for more than 6 months without the risk of re-stacking. This method paves the way for the environmentally friendly and cost-effective production of graphene-based materials.

Efficient exfoliation of layered materials by waste liquor.

Based on their unique material properties, two-dimensional (2D) nanomaterials such as graphene, molybdenum disulfide (MoS2), and boron nitride (BN) have been attracting increased research interest. The potential of 2D materials, in the form of nanoplatelets that are used as new materials, will be important to both nanomaterials and advanced materials. Water is usually considered to be the ideal dispersed medium, and the essential hydrophobicity and limitations to mass production of 2D nanoplatelets have become quite serious obstacles to their usage in various fields. In this paper, pulping black liquor was used as dispersant, with high concentration of lignin to get single- and few-layered nanoplatelets. The whole process required only the high-shear mixing of 2D layered materials and pulping waste liquor. This method was not only simple and efficient but also environmentally friendly and resource-recycling. Moreover, the fabricated single- or few-layered nanoplatelets possessed good solubility in aqueous solution due to their edge functionalization, and could be well dispersed in water at concentrations (10 mg ml-1 for graphene, 6.3 mg ml-1 for MoS2, and 6.0 mg ml-1 for BN) which were much higher than that of other methods. The dispersions of graphene, MoS2, and BN nanosheets were highly stable over several months, which allowed us to easily prepare graphene, MoS2, and BN films through simple vacuum filtration or spraying. These results indicated that pulping black liquor can be used as a material or reagent, and the mass production of 2D material is possible in a simple and fast method.

An ultrahigh thermal conductive graphene flexible paper.

Graphene nanosheets (GNSs) possess outstanding conductivity, good thermal and chemical stabilities and desirable mechanical strengths. However, the unfunctionalized GNSs are hydrophobic and insoluble in water, which limits their application in many technological areas. Herein, we report a design strategy to exfoliate few-layered aqueous dispersible graphene by a simple ball-milling technique. The modifier of sodium lignosulfonate (LS) enables to synthesize LS-decorated GNSs from natural graphite based on the strong π-π interaction, greatly improving GNSs dispersion in water. The resultant GNSs exhibit a high production yield (∼100%), high dispersion concentration and excellent film formation ability. The electrical and thermal conductivities of the as-prepared graphene paper were up to 2385 S cm-1 and 1324 W m-1 K-1, respectively, superior to those of most previously reported graphene materials. This graphene paper with the superb electrical and thermal conduction properties also exhibits excellent mechanical flexibility and structure intensity during bending, which has potential usages in electronic packaging and high power thermal management.

Ultrahigh performance heat spreader based on gas-liquid exfoliation boron nitride nanosheets.

Due to their high thermal conductivity and insulation performance, boron nitride nanosheets (BNNS) have great promise to fabricate thermal management equipment for application in power electronics. The liquid-phase exfoliation route has been regarded as the most commonly used approach to produce single and few-layered BNNS for many research fields. However, this process takes a long time, and the production yield is extremely low. In this work, an efficient technique to obtain few-layered (mostly < 5 layers), high-yield (∼33%), and plane-defect-free BNNS by the combination of liquid N2 (L-N2) gasification and liquid exfoliation was developed. The as-obtained BNNS suspensions could be vacuum filtered to make a thermal conductive film named a BNNS heat spreader which possessed a superior thermal conductivity of 61.2 W m-1 K-1 at room temperature. In addition, we also proved that the thermal conductivity of the BNNS heat spreader increased with the increase of density, creating an approach for fine tuning the thermal property of this heat spreader.

Hydroxylated graphene-based flexible carbon film with ultrahigh electrical and thermal conductivity.

Graphene-based films are widely used in the electronics industry. Here, surface hydroxylated graphene sheets (HGS) have been synthesized from natural graphite (NG) by a rapid and efficient molten hydroxide-assisted exfoliation technique. This method enables preparation of aqueous dispersible graphene sheets with a high dispersed concentration (∼10.0 mg ml-1) and an extraordinary production yield (∼100%). The HGS dispersion was processed into graphene flexible film (HGCF) through fast filtration, annealing treatment and mechanical compression. The HGS endows graphene flexible film with a high electrical conductivity of 11.5 × 104 S m-1 and a superior thermal conductivity of 1842 W m-1 K-1. Simultaneously, the superflexible HGCF could endure 3000 repeated cycles of bending or folding. As a result, this graphene flexible film is expected to be integrated into electronic packaging and high-power electronics applications.