Xiu-Zhi Tang

Robust microcapsules with polyurea/silica hybrid shell for one-part self-healing anticorrosion coatings

Silica/polyurea hybrid microcapsules loaded with hexamethylene diisocyanate (HDI) as core materials were prepared via a combined strategy of interfacial polymerization and an in situ sol–gel process in an oil-in-water emulsion. They were clearly characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The resultant microcapsules have diameters of 57–328 μm, shell thicknesses of 1–8 μm, and core fractions of 51.2–65.6%. The diameter and shell thickness were linearly related to the agitation rate in the double logarithm coordinates, and the core fraction were linearly related to the agitation rate, indicating that the structure and component of the microcapsules can be controlled effectively. The resistant properties against thermal and solvent attacks were assessed by using thermogravimetric analysis and titration. The results show that the microcapsules had outstanding thermal stability with initial evaporation temperature (defined at 5% of weight loss), increased by around 58 °C compared with that of pure core material, and good resistance to xylene with less than 25.9 ± 0.7 wt% reduction of core content after immersion for 100 h. Self-healing anticorrosion coatings based on microcapsules were fabricated on a steel substrate. Preliminary results indicated significant corrosion retardancy occurred in the coatings under an accelerated corrosion process, showing the great potential of our microcapsules in the development of catalyst-free, one-part, self-healing coatings for corrosion control.

Enhanced Molecular Level Dispersion and Interface Bonding at Low Loading of Modified Graphene Oxide To Fabricate Super Nylon 12 Composites

Development of advanced graphene based polymer composites is still confronted with severe challenges due to its poor dispersion caused by restacking, weak interface bonding, and incompatibility with polymer matrices which suppress exertion of the actual potential of graphene sheets in composites. Here, we have demonstrated an efficient chemical modification process with polyethylenimine (PEI) to functionalize graphene oxide which can overcome the above-mentioned drawbacks and also can remarkably increase the overall strength of the nylon 12 composites even at very low graphene loading. Chemical modification was analyzed by various surface characterizations including X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. Addition of only 0.25 and 0.35 wt % modified GO showed 37% and 54% improvement in tensile strength and 65% and 74% in Youngs modulus, respectively, compared with that of the neat polymer. The dynamic mechanical analysis showed ∼39% and 63% increment in storage modulus of the nanocomposites. Moreover, the nanocomposites exhibited significantly high thermal stability (∼15 °C increment by only 0.35 wt %) as compared to neat polymer. Furthermore, the composites rendered outstanding resistance against various chemicals.

Mechanical, tribological and biological properties of novel 45S5 Bioglass® composites reinforced with in situ reduced graphene oxide

45S5 Bioglass® (45S5) is one of the most widely used biomaterials in ceramic-based bone graft substitutes by virtue of its excellent biocompatibility and bioactivity. However, the fracture toughness and wear resistance of 45S5 have to be improved to extend its applications in load bearing orthopedic implants. The current study reports the first use of graphene nanoplatelet (GNP) to enhance the fracture toughness and wear resistance of 45S5. Composite powders with four different loadings of graphene oxide (GO), i.e. 0, 0.1, 0.5 and 1wt%, were sintered by spark plasma sintering (SPS) at a relatively low temperature of 550°C, during which in situ thermal reduction of GO took place. It was found that by adding 0.5wt% GO to the 45S5 powder, the fracture toughness of the sintered pellets was increased by 130.2% while friction coefficient and specific wear rate were decreased by 21.3% and 62.0%, respectively. Furthermore, the viability of MG63 cells grown on the GNP-incorporated pellets was comparably high to that of the cells grown on the pure 45S5 pellets. As compared with the pure 45S5 leachates, the media conditioned by the GNP/45S5 pellets fabricated from the composite powder with 1wt% GO could enhance both the proliferation and viability of MG63 cells. It is thus envisioned that the GNP-reinforced 45S5 is a highly promising material for fabricating mechanically strong and biocompatible load-bearing bone implants.

Single-Step Process toward Achieving Superhydrophobic Reduced Graphene Oxide

We report the first use of spark plasma sintering (SPS) as a single-step process to achieve superhydrophobic reduced graphene oxide (rGO). It was found that SPS was capable of converting smooth and electrically insulating graphene oxide (GO) sheets into highly electrically conductive rGO with minimum residual oxygen and hierarchical roughness which could be well retained after prolonged ultrasonication. At a temperature of 500 °C, which is lower than the conventional critical temperature for GO exfoliation, GO was successfully exfoliated, reduced, and hierarchically roughened. rGO fabricated by only 1 min of treatment at 1050 °C was superhydrophobic with a surface roughness (Ra) 10 times as large as that of GO as well as an extraordinarily high C:O ratio of 83.03 (atom %) and water contact angle of 153°. This demonstrates that SPS is a superior GO reduction technique, which enabled superhydrophobic rGO to be quickly and effectively achieved in one single step. Moreover, the superhydrophobic rGO fabricated by SPS showed an impressive bacterial antifouling and inactivation effect against Escherichia coli in both aqueous solution and the solid state. It is envisioned that the superhydrophobic rGO obtained in this study can be potentially used for a wide range of industrial and biomedical applications, such as the fabrication of self-cleaning and antibacterial surfaces.

Short Carbon Fiber-Reinforced Epoxy Tribomaterials Self-Lubricated by Wax Containing Microcapsules

The effects of wax lubricant filled microcapsule content on the tribological properties of epoxy composites without or with 8wt.% short carbon fibers (SCFs) were systematically investigated. The core percentage of the microcapsules used in this study was about 70wt.%. The tribological results clearly showed that the friction and wear of the epoxy composites without or with SCFs tested against a 6mm steel ball significantly decreased with increased microcapsule content from 2.5 to 10wt.% as a result of the increased amount of released wax lubricant to lubricate rubbing surfaces. The epoxy composites with 8wt.% SCFs exhibited the lower friction and wear than the ones without SCFs due to the combined lubricating effects of SCFs and released wax lubricant and the improved mechanical strength of the composites. It can be concluded that the higher microcapsule content gives rise to the lower friction and wear of the epoxy composites as the epoxy composites with 8wt.% SCFs have the better tribological performance than the ones without SCFs. [DOI: 10.1115/1.4028752]

Polydopamine decoration on 3D graphene foam and its electromagnetic interference shielding properties

3D graphene foam was recently demonstrated to exhibit excellent electromagnetic interference (EMI) shielding performance. In this work, we prepared 3D graphene foams by incorporating a surface modification process of graphene via self-polymerization of dopamine with a subsequent foaming process. The multiple roles played by polydopamine (PDA), including as nitrogen doping source and as an enhancement tool to achieve higher extent of reduction of the graphene through providing wider pathways and larger accessible surface areas were discussed in detail. Despite the presence of the PDA which acted as barriers among the graphene layers that hindered the electrons movement, the enhanced reduction of graphene sheets and the polarization effects introduced by PDA decoration compensated the negative effect of the barrier on EMI shielding effectiveness (SE). As a result, the PDA decorated 3D graphene foams showed improved EMI shielding effectiveness (SE) compared to PDA-free graphene foam (from 23.1 to 26.5dB). More significantly, the EMI shielding performance of the PDA decorated graphene foam was much superior to all existing carbon-based porous materials when the thickness of the specimen was considered.

Improved chemical stability of silver by selective distribution of silver particles on reduced graphene oxide nanosheets

The chemical stability of particles on reduced graphene oxide (RGO) nanosheets is an important issue for the RGO/particles hybrid materials. Here we report that the chemical stability of environmentally sensitive silver can be significantly improved by controlling the distribution of silver particles on RGO nanosheets. By switching the sequence of “deoxygenation” and “deposition”, two kinds of RGO/silver hybrids are prepared. The structure and chemical state of silver particles on RGO are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, ultraviolet-visible spectroscopy, Raman spectra, transmission electron microscopy and scanning electron microscope. It is found that the graphene/Ag hybrid prepared by “deposition” and then “deoxygenation” can still exhibit obvious surface enhanced Raman scattering (SERS) signals after 10-month storage, compared with the hybrid material fabricated in inverse order. The selective distribution of silver particles and non-uniform dispersion of electrons on RGO nanosheets are responsible for the different performances. This study provides a new insight into preparing chemically stable RGO/particle hybrid materials.

Controlled thermal functionalization for dispersion enhancement of multi-wall carbon nanotube in organic solvents

AbstractDespite extensive study on carbon nanotube (CNT), the proliferation of its real applications has been hindered by its dispersibility in various organic or inorganic media. Very often complex surface functionalization processes are required to endow CNTs with enhanced dispersibility. Hence, facile, high-yield, and scalable functionalization methods for CNT for better dispersion are highly desirable. Thermal annealing is sometimes adopted for purification of CNT; however, limited discussion has been devoted to its functionalization effect and surface chemistry, which directly determine CNT dispersibility. In this work, via controlled mild thermal annealing, enhanced dispersion of functionalized CNTs was achieved in different organic solvents, including ethanol, dimethyl formamide, chloroform and acetone. Such enhancement had been studied through qualitative (dispersion and sedimentation, TEM) and quantitative analyses (XPS, Raman) of morphological structures and chemical states of thermally functionalized CNTs. The analyses reveal that under mild thermal annealing conditions, the surface oxidative reactions of the CNT can be well controlled, with minimal damage to the graphitic structure of the CNT. A plausible functionalization mechanism involving ether and quinone functional groups is proposed. The advantages of thermal annealing toward enhanced dispersion are further demonstrated by employing the functionalized CNT in poly (vinylidene fluoride) composite and drop-cast conductive CNT pattern.

Reduced graphene oxide/silver hybrid with N,N-dimethyl formamide for oxygen reduction reactions and surface enhanced Raman scattering

A reduced graphene oxide (RGO)/Ag hybrid for oxygen reduction reaction and surface enhanced Raman scattering was prepared and a reasonable reaction path towards the reduction of graphene oxide (GO) was investigated. The structures and properties of RGO and RGO/Ag were characterized by various methods, such as Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and thermal gravity analysis. The results indicated that the reduction time for GO treated by N,N-dimethyl formamide (DMF) only had slight effect on the reduction degree of RGO; however, the hydrophobicity of RGO increased dramatically with the increasing reaction time, owing to the introduction of hierarchical structures. Instead of the traditional opinion on the DMF involved hydrolysis, we proposed a new possible reaction path rendering the chemical structure of the obtained RGO more reasonable. Furthermore, the obtained RGO/Ag demonstrated to be useful for surface enhanced Raman scattering and an effective catalyst for oxygen reduction reaction. This work was expected to provide inspiration for promoting the synthesis and applications of inorganic particles-decorated RGO hybrids.