Junfang Ren

Tribology Study of Reduced Graphene Oxide Sheets on Silicon Substrate Synthesized via Covalent Assembly

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.

Cooperatively exfoliated fluorinated graphene with full-color emission

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.

Non-isothermal crystallization kinetics of PA6/attapulgite composites prepared by melt compounding

The non‐isothermal crystallization behaviors of neat polyamide 6 (PA6) and PA6/attapulgite (ATB) composites were examined using differential scanning calorimetry. The results show that ATB acts as a nucleator for PA6 matrix, accelerating the crystallization, and simultaneously obstructs the crystallization especially for the composites with higher ATB content. The analysis results using the Jeziorny and Liu equations verify the dual actions of the nucleation and the obstruction of crystallization of the ATB in the PA6 matrix. Kissingers method is employed to obtain the activation energy of the crystallization processes; the results further indicate that the addition of ATB may also cause the above actions. It is speculated that there is a very complicated crystallization mechanism in the PA6/ATB composites based on the analysis of Avrami exponents obtained by the Jeziorny model.

Tribological Behavior of Nano-Al2O3-Reinforced PPS-PTFE Composites

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.

Morphological, Thermal and Mechanical Properties of Compatibilized Nylon 6/ABS Blends

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.

Study on the Morphological and Mechanical Properties of Nylon 6/ABS/Nano-SiO2 Composites

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.

Friction and Wear Behavior of Polyamide 66/Poly(vinylidene fluoride) Blends

The tribological performance of PA66 and PVDF blends was investigated by a block‐on ring sliding friction and wear tester. The appropriate amount of PVDF can decrease the friction coefficient and improve the wear resistance of PA66. Moreover, the appropriate amount of PA66 can improve the wear resistance of PVDF. SEM analysis shows that PVDF is noncompatible with PA66, and the blend presents a two‐phase structure. A smooth worn surface is a main reason for improving the frictional and wear properties of the PA66/PVDF blend. Besides, slight debris is an important factor in improving the wear resistance of the PA66/PVDF blend. FT‐IR analysis shows that the oxidation and degradation behavior of PVDF is effectively controlled in the PA66/PVDF blends. Therefore, the blend of PA66 and PVDF is a potential polymer material for tribological applications.

Synergistic effects of titanium dioxide and cellulose on the properties of glassionomer cement

In this study, we evaluate the effect of co-doping with TiO2 nanoparticles and sisal cellulose nanocrystals (CNCs) on the physical and biological properties of a conventional glass-ionomer cement (GIC). Test samples were characterized by scanning electron microscopy, and Fourier-transform infrared spectroscopy, and subjected to mechanical tests to evaluate the mechanical performances. Antimicrobial activity was evaluated against Candida albicans, and cytotoxicity experiments were conducted using L-929 cells. Unmodified GIC served as a control. Compared with the control group, the co-doped group demonstrated an increased compressive strength of 18.9%, an increased shear bond strength of 51%, the dissolution decreased by 18.3%, the volume wear rate was reduced by 5%. The antifungal effect against C. albicans was increased by 22%. In cytotoxicity experiments, the co-doped group had a slightly negative effect on the viability of L-929 cells.