[Show abstract][Hide abstract] ABSTRACT: Graphene decorated with well-dispersed cubic fluorite ceria (CeO2) nanoparticles was prepared through a simple hydrothermal method. The as-prepared CeO2/graphene composites (COGNCs) were further used as lubricant additives in the base oil of liquid paraffin to investigate their tribological properties by the Optimol SRV-1 oscillating reciprocating friction and wear tests in air (relative humidity, 17%). The results indicated that the introduction of a small amount of COGNCs into the base oil could reduce friction and wear drastically under a high load condition, which was better than the testing results of graphene or CeO2 nanoparticles. Specifically, when 0.06 wt% COGNCs was added into the base oil, the average friction coefficient could be reduced from 0.21 to 0.10, and the wear rate could be decreased to 1.5% of that of base oil. The excellent tribological properties of COGNCs can be explained by the synergistic friction reduction and antiwear effects of graphene and CeO2 nanoparticles.
[Show abstract][Hide abstract] ABSTRACT: A novel multi-layered nanocomposite film, abridged as ZrO2/GO (zirconia/graphene oxide), was constructed by a simple layer-by-layer (LBL) self-assembly process. It is expected that the key factor for constructing such a film is the high surface activity of GO nanosheets with various oxygen-containing groups, which ensures the strong bonding with substrate and facilitates the deposition of ZrO2 thin film thereon. The as-constructed film after fifteen cycle deposition with a thickness of 170-260 nm shows outperformed tribological performances (with the friction coefficient of 0.13 ~ 0.17 and anti-wear life of longer than 6000 s) and mechanical property (with a hardness of 12.74 GPa) even without annealing. These outperformed properties are probably ascribed to the multi-layered nanostructures and the synergistic effect of the excellent tribological/mechanical properties of GO nanosheets as well as ZrO2 nanoparticles. Furthermore, after being annealed at 500 °C or 900 °C, the film still presents lower friction coefficient (0.11 ~ 0.14) under the same test conditions. It is expected that this ZrO2/GO multi-layered nanocomposite film can be wildly used as protecting or/and lubricating coating for micro- and nano-electromechanical systems (MEMS/NEMS) not only for its excellent tribological/mechanical properties but also for its simplicity and feasibility of such a construction process.
[Show abstract][Hide abstract] ABSTRACT: The composite of polytetrafluoroethylene (PTFE) has been generally applied to dynamic seals in Stirling power systems due to its excellent self-lubrication and resilience. In this article, the tribological behavior of polyphenylene sulfide (PPS)-PTFE blends filled with nano-Al2O3 are investigated under different contact loads, sliding speed, and operating temperatures using a block-on-ring friction and wear tester. The results indicate that the addition of nano-Al2O3 could significantly improve the antiwear performance of the PPS-PTFE blend. Nano-Al2O3-filled PPS-PTFE composites have good tribological performance under high-temperature environments. When the content of nano-Al2O3 is 5 wt%, the wear rate of the composite is 276 times better than that of virgin PTFE and more than 150 times better than that of unfilled PPS-PTFE. Dynamic mechanical analysis (DMA) shows that the block of the movement of molecular chains of PTFE with the addition of nano-Al2O3 particles may be responsible for the significant decrease in the wear rate. The greatest impact on the antiwear performance of the composite for Stirling engines is load, followed by temperature, and the minimum effect is due to sliding velocity.
[Show abstract][Hide abstract] ABSTRACT: Tunable control over the functionalization of graphene is significantly important to manipulate its structure and optoelectronic properties. Yet the chemical inertness of this noble carbon material poses a particular challenge for its decoration without forcing reaction conditions. Here, a mild, operationally simple and controllable protocol is developed to synthesize hydroxylated graphene (HOG) from fluorinated graphene (FG). We successfully demonstrate that under designed alkali environment, fluorine atoms on graphene framework are programmably replaced by hydroxyl groups via a straightforward substitution reaction pathway. Element constituent analyses confirm that homogeneous C-O bonds are successfully grafted on graphene. Rather different from graphene oxide, the photoluminescence (PL) emission spectrum of the obtained HOG becomes split when excited with UV radiation. More interestingly, such transformation from FG facilitates highly tunable PL emission ranging from greenish white (0.343, 0.392) to deep blue (0.156, 0.094). Additionally, both experimental data and density function theory calculation indicate that the chemical functionalization induced structural rearrangement is more important than the chemical decoration itself in tuning the PL emission band tail and splitting energy gaps. This work not only presents a new way to effectively fabricate graphene derivatives with tunable PL performance, but also provides an enlightening insight into the PL origin of graphene related materials.
[Show abstract][Hide abstract] ABSTRACT: We have explored a novel photochemical route to synthesize fluorinated graphene via simultaneously fluorinating and reducing graphene oxide (GO) in HF solution at room temperature. This method avoids special equipment, employs simple UV irradiation and utilizes readily available GO as the carbon source.
[Show abstract][Hide abstract] ABSTRACT: Casein phosphopeptides (CPPs) with abundant phosphoserine clusters can mediate hydroxyapatite (HA) nucleation and growth. In this work, a new type of CPPs-biofuctionalized graphene composite was synthesized by amidation reaction between CPPs and carboxyalated graphene (CGO). When immersed in stimulated body fluid (1.5 × SBF) at 37 °C for different periods, the CPPs layer on the composite facilitated efficient interaction between the CGO surface and mineral ions, which promoted HA nanoparticle formation and shortened mineralization time in comparison with pristine CGO. The synthesis of the composite mimicked the natural biomineralization of bone, demonstrating that CPPs can effectively improve the bioactivity of graphene and be useful for HA formation. The presented biocomposite may have potential biomedical applications in different areas.
The Journal of Physical Chemistry C. 01/2013; 117(20):10375-10382.
[Show abstract][Hide abstract] ABSTRACT: An easy, low-cost and effective synthesis of fluorinated graphene with tunable C/F atomic ratio (RC/F) has been realized by the reaction between dispersed graphene oxide and hydrofluoric acid. The results show that fluorine is grafted onto the basal plane of graphene, and the RC/F can be easily adjusted by controlling the reaction conditions. The as-synthesized fluorinated graphene exhibits a sheet-like morphology with 1–2 layered thickness and tunable bandgap energy from 1.82 to 2.99 eV, which has potential applications in optoelectronic and photonic devices.
[Show abstract][Hide abstract] ABSTRACT: We report a novel and effective method to prepare fluorinated graphene sheets (FGS) by the cooperative exfoliation of graphite fluoride using cetyl-trimethyl-ammonium bromide and dopamine. This facile, scalable preparation route results in wide (about 2 μm in width), long (at least 3 μm in length) and ultrathin (1–2 layers) FGS with uniform morphology. The chemical composition of FGS was characterized by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The obtained FGS exhibits full-color emission when excited by near ultraviolet (NUV) rays, suggesting its potential applications in luminescence devices, such as NUV-pumped FGS-based flexible light-emitting diodes.
[Show abstract][Hide abstract] ABSTRACT: Fluorographene (FG), which inherits the properties of graphene and fluorographite (FGi), holds great promise for applications in high-performance materials and devices, including lubricants, nanocomposites, batteries, and nanoelectronics. However, challenges for realizing large-scale preparation and little knowledge concerning FG's physicochemical properties hinder its practical applications. Here, a novel and feasible method is developed to prepare FG through a simple sonochemical exfoliation process in N-methyl-2-pyrrolidone (NMP). Interestingly, FG at a high concentration in NMP displays dramatic stability without any additional stabilizer or modifier, and the C/F ratio of FG can be facilely tuned just by adjusting the sonochemical time. Furthermore, the electrochemical and thermal properties of the prepared FG have been systematically investigated and exhibited regularity with variation of fluorine coverage. On the other hand, based on the solubility of FG in various solvents, a possible dispersion mechanism is proposed to guide FG's further applications in films or polymer-based composites as a mechanical reinforcement.
Journal of Materials Chemistry 07/2012; 22(33):16950-16956. · 5.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work, we present a simple and feasible method with broad applicability for the in-situ reduction and assembly of graphene lubricant films on various substrates. We adopt graphene oxide hydrosol as the precursor solution and creatively introduce an adherent coating of polydopamine that can be firmly bonded onto a wide range of substrates and acts as an active transition layer and in-situ reducing agent, aiming at obtaining the reduced graphene oxide (rGO) films thereon without addition of exogenous reducing agent. Experimental results prove that rGO nanosheets have been successfully assembled onto the substrates and the in-situ synthesized rGO film presents excellent morphology, outstanding friction reduction and wear resistance properties.
Journal of Materials Chemistry 03/2012; 22(16):8036-8042. · 5.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Reduced graphene oxide (RGO) sheets were covalently assembled onto silicon wafers via a multistep route based on the chemical adsorption and thermal reduction of graphene oxide (GO). The formation and microstructure of RGO were analyzed by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, Raman spectroscopy, and water contact angle (WCA) measurements. Characterization by atomic force microscopy (AFM) was performed to evaluate the morphology and microtribological behaviors of the samples. Macrotribological performance was tested on a ball-on-plate tribometer. Results show that the assembled RGO possesses good friction reduction and antiwear ability, properties ascribed to its intrinsic structure, that is, the covalent bonding to the substrate and self-lubricating property of RGO.
[Show abstract][Hide abstract] ABSTRACT: The mechanical properties and morphology of the composites of nylon 6, acrylonitrile-butadiene-styrene (ABS) rubber, and nano-SiO2 particles were examined as a function of the nano-SiO2 content. A mixture with separation and encapsulation microstructures existed in the nylon 6/ABS/nano-SiO2 at lower nano-SiO2 content, and ABS and nano-SiO2 improved the toughness synergistically, while obvious agglomeration appeared at higher nano-SiO2 content and the impact strength decreased. Moreover, the addition of nano-SiO2 particles also affected the dispersion of the rubber phase, resulting in the appearance of smaller rubber particles. The deformation and toughening mechanisms of the composites were also investigated; they resulted from rubber voiding, crack forking, and plastic deformation of the matrix.
Journal of Macromolecular Science Part B 11/2009; Part B(Vol. 48):1069-1080. · 0.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Polyamide (PA) 66/PP-g-MA/Organic-modified MMT (OMMT) ternary composites were prepared by direct melt compounding. The FESEM results showed that the PP-g-MA phase dispersed homogeneously in the PA matrix due to the interfacial chemical reactions between the two phases. The mechanical properties of the composites were evaluated. The tensile and bending properties decreased and the notched impact strength increased with the increase of PP-g-MA. The tribological behaviors of the ternary composites were studied by means of a ball-on-disk apparatus. The ternary composites exhibited better tribological properties compared with the PA/OMMT system. This was probably due to the fact that the PP has good flexibility and a transferring film could be formed easily on the counterpart. Combining the results of the mechanical and tribological properties, the optimal mass fraction of PP-g-MA was 10 wt. %.
Journal of Macromolecular Science Part B 01/2009; 48(1):55-67. · 0.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Super‐tough nylon 6/ABS blends were prepared by using styrene/acrylonitrile/maleic anhydride co‐polymer (SAM) as a compatibilizer. The variations in morphology, mechanical behavior, and crystallinity associated with the reaction of the SAM with the nylon were characterized. The results showed that the addition of SAM to nylon 6/ABS blends enhanced the interfacial adhesion between nylon 6 and ABS, and this led to the decrease of ABS domain size and the improvement of mechanical properties of their blends. Moreover, it could be found that the crystallinity and phase morphology changed with the variation of SAM.
Journal of Macromolecular Science Part B 01/2008; Part B: Physics(Vol. 47):712-722. · 0.63 Impact Factor