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Silicon is a promising photocathode material in photoelectrochemical water splitting for hydrogen production, but it is primarily limited by photocorrosion in aqueous electrolytes. As an extensively used protective material, crystalline TiO2 could protect Si photoelectrode against corrosion. However, a large number of grain boundaries (GBs) in polycrystalline TiO2 would induce excessive recombination centers, impeding the carrier transport. This paper describes the introduction of oxygen vacancies (Ovac ) with controllable spatial distribution for GBs to promote carrier transport. Two kinds of Ovac distribution, Ovac along GBs and Ovac inside grains, are compared, where the latter one is demonstrated to facilitate carrier transport owing to the formation of tunneling paths across GBs. Consequently, a simple p-Si/TiO2 /Pt heterojunction photocathode with controllable Ovac distribution in TiO2 shows a +400 mV onset potential shift and yields an applied bias photon-to-current efficiency of 5.9 %, which is the best efficiency reported among silicon photocathodes except for silicon homojunction.

Water‐coal interactions have gained much recent attention, although few studies focus on the strength of coal under wetting‐drying cycles. This study investigates changes in the microstructure and mechanical strength of coal that are induced by water‐coal interactions, at the macroscale and microscale. Fourteen specimens after continuous wetting and fourteen specimens after wetting‐drying cycles were tested, indicating that peak stress and elastic modulus decrease with increasing continuous wetting time and number of wetting‐drying cycles, while peak strain increases. We analyzed changes in the coal microstructure using a scanning electron microscope (SEM) and the Image Pro Plus 6.0 (IPP 6.0) software. The regression model for cyclic wetting‐drying reveals that porosity and pore circularity are the main correlation indicators associated with uniaxial compressive strength. Therefore, different numbers of wetting‐drying cycles could induce different degrees of damage to coal, which increases progressively through gradual changes to its microstructure. These findings indicate that wetting‐drying cycles have a more significant impact on the stability of coal mass than continuous wetting. Our results are of use in determining the size of coal pillars, and expanding the knowledge base related to the mechanical properties of coal mass, water bursting, water recharge channels, and the stress‐crack‐permeability evolution law in mines.

Owing to the increasing power density of miniaturized and high-frequency electronic devices, flexible thermal interface materials (TIMs) with the electromagnetic interference (EMI) shielding property are in urgent demand to maintain the system performance and reliability. Recently, carbon-based TIMs receive considerable attention due to the ultrahigh intrinsic thermal conductivity (TC). However, the large-scale production of such TIMs is restricted by some technical difficulties, such as production-induced defects of graphite sheets, poor microstructure architecture within the matrix, and nonnegligible interfacial thermal resistance result from the strong phono scattering. In this work, inspired by the structure and production process of millefeuille cakes, a unique double self-assembly strategy for fabricating ultrahigh thermal conductive TIMs with superior EMI shielding performance is demonstrated. The percolating and oriented multilayered microstructure enables the TIM to exhibit an ultrahigh in-plane TC of 233.67 W m-1 K-1 together with an outstanding EMI shielding effectiveness of 79.0 dB (at 12.4 GHz). In the TIM evaluation system, a nearly 45 °C decrease is obtained by this TIM when compared to the commercial material. The obtained TIM achieves the desired balance between thermal conduction and EMI shielding performance, indicating broad prospects in the fields of military applications and next-generation thermal management systems.

A novel electrochemical technique had been introduced to prepare nanocrystalline superamphiphobic coatings inside of narrow pipes of significant length. The axially propagated ultrasound was utilized to ensure the scaling-up potential of this technique. The coating had strong mechanical strength, durability in low/high pH solutions and the potential of controlling its thickness while preserving a stable nonwetting performance. In addition, the properties of anti-scaling and drag reduction under the flowing circumstance had been demonstrated. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3636–3641, 2017

Microcapsules containing an ionic liquid (IL) are potential candidate materials for preparing in situ self-lubricating composites with excellent tribological properties. 1-ethyl-3-methylimidazolium bis[(trifluoromethyl) sulfonyl]imide ([EMIm]NTf2) IL encapsulated polysulphone microcapsules are synthesized. The mean diameter and wall thickness are about 128 μm and 10 μm, respectively. Microcapsules have excellent thermal stability, with a thermal degradation onset temperature of 440 °C compared to traditional lubricants-loaded microcapsules. In situ self-lubricating composites are prepared by incorporating the IL-encapsulated microcapsules into epoxy matrix. When the concentration of the IL microcapsules is 20 wt%, the frictional coefficient and specific wear rate of composites are reduced by 66.7% and 64.9% under low sliding velocity and middling applied load conditions, respectively, as compared to the neat epoxy. The tribological behavior of the self-lubricating composites is further assessed in different applied load and sliding velocity conditions. The in situ self-lubricating mechanism of composites is proposed.

The polyimide (PI) fabric/epoxy (EP) composites modified with different content of micro-SiO2 hollow spheres were prepared by dip-coating and subsequently hot-press process. For comparison, the pure EP and the unmodified PI fabric/EP composite were also fabricated. The differential scanning calorimetry was conducted to investigate the crosslinking reaction of composites. The results indicated that there exhibited a remarkable improvement in the mechanical and tribological properties of PI fabric/EP composites after incorporating the micro-SiO2. The best tribological properties were obtained when the content of micro-SiO2 was 2 wt%, whose wear rate was 71.9% lower than that of unmodified PI fabric/EP composite. The worn surfaces were observed by a scanning electron microscope to illustrate the friction mechanisms. Note that the skeleton network structure of fabric throughout the whole composites supported the matrix. At the same time, the microparticulates filled in the interstices of fabrics interwoven structure and the gaps between layers of fabrics, which propped up the skeleton network of fabric under the high frictional load and afford excellent interface between fabrics and EP. This ensures the outstanding tribological properties of PI fabric/EP composites. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

A functionalization process with dopamine on multiwalled carbon nanotubes (MWNTs) has been carried out in order to enhance the tribological properties of MWNTs/epoxy resin (EP) composites. Dopamine modification is of signality for the performance of MWNTs/EP composites. The hardness and flexural strength of the composites were significantly improved with the incorporation of dopamine modified MWNTs, owning to the enhanced interfacial bonding between MWNTs and EP. Meanwhile, the thermal characterizations indicated that dopamine played an important role in improving the thermal stability of MWNTs/EP composites. More importantly, the friction and wear properties of dopamine modified MWNTs/EP composites were enhanced considerably and its wear rate was 85.8% lower than that of pure EP. Dopamine modified MWNTs were linked with the matrix by strong covalent bond to form a great network structure and impeded the movement of polymer molecule chains in the composites. Then the friction load transmitted efficiently through the network structure and the plastic deformation was restrained as well as the initiation and growth of cracks on the worn surfaces. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

A self-assembling molecule, n-octadecane phosphate, is successfully synthesized and used to modify the surface property of carbon nanofibers (CNFs). Both untreated CNFs (CNFs(u)) and treated CNFs ( ...

Nano-micro hierarchical porous polyphenylene sulfide/polytetrafluoroethylene (PPS/PTFE) composites were prepared by mold-leaching and vacuum melting process under high temperature condition. The tribological behaviors of porous PPS/PTFE composites and the synergism as a result of incorporation of both micro-porogen (NaCl) and mesoporous TiO2 whiskers were investigated. The effects of mesoporous TiO2 whiskers and nonperforated TiO2 whiskers on the friction and wear properties of PPS/PTFE composites were comparatively studied, respectively. Results indicated that the wear rate of porous PPS/PTFE composites with 30 wt % NaCl and 7 wt % mesoporous TiO2 whiskers obtained the lowest values under the load of 100 N. Compared with pure PPS, the wear resistance of nano-micro porous PPS/PTFE composite was enhanced by 6.45 × 103 times, showing outstanding wear resistance. During sliding condition, grease could be squeezed through the nano-micro pores under the coupling effect of load and friction heat, and formed a lubricanting layer on friction surface, providing self-lubricating effect and high wear resistance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Novel epoxy (EP) composite reinforced with three-dimensional (3D) polyimide (PI) fiber felt (PI3D/EP) is first fabricated by vacuum assisted resin transfer molding. The tribological behaviors of pure EP and PI3D/EP composite under dry sliding and water lubricated condition are comparatively studied. Results indicate that both wear rates and friction coefficients of PI3D/EP composite are lower than those of pure EP. The wear resistance of PI3D/EP composite is 9.8 times higher than that of pure EP under dry sliding of 1.5 MPa and 0.76 m s−1 while a 27-fold increase is achieved under water lubricated condition. The wear mechanisms of PI3D/EP composite are investigated based on tribological testing results and scanning electron microscopy observations. The PI fiber felt provides strong 3D structure supports to sustain most of the loads on the composite, improving the mechanical and tribological properties significantly. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44160.

The tribological properties and mass loss of polytetrafluoroethylene (PTFE) composites filled with carbon fiber (CF) or potassium titanate whisker (PTW) after the immersion in 30% sulfuric acid solution for 5 or 15 days were studied under different temperatures (25, 50, and 75°C). Results show that PTW/PTFE composites exhibit better anticorrosive and antiwear properties than those of CF/PTFE composites. Acid immersion has no obvious effect on the wear rate of the PTW/PTFE composite. The wear rate of CF/PTFE immersed for 15 days is thrice as much that of untreated composites and 3.6 times as much that of PTW/PTFE composites. Results also indicate that the wear rate of PTFE composites increases with the increasing corrosive mass loss rate and is more dependent on the corrosive mass loss rate rather than the friction coefficient. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The friction and wear properties of poly (ether ether ketone) (PEEK) composites filled with potassium titanate whiskers (PTWs) under alkali, water, and dry conditions were investigated. The wear mechanisms in different lubrication situations were studied on the basis of examinations of the worn and counterpart surfaces with scanning electron microscopy and optical microscopy. The results showed that PTWs could obviously increase the wear resistance and reduce the friction coefficient of the PEEK composites under dry sliding conditions. Only when the PTW content was greater than 35 wt % did the wear resistance and friction coefficient deteriorate. Sliding in water caused increases in the wear rate and friction coefficient of the PEEK composites, and the PTW-filled PEEK composites showed the highest friction coefficient and wear rate under this lubrication condition. On the contrary, sliding in an alkaline solution, the PTW-filled PEEK composites showed the lowest friction coefficient and almost the same level of wear resistance as that found under the dry condition. Furrows and abrasive wear were the main mechanisms for the PTW-filled PEEK composites sliding in water. The transfer onto the counterpart rings was significantly hindered with sliding under water and alkali conditions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The effects of various filler concentrations (0.1, 0.5, 1, 1.5, 2, 2.5, and 3 wt %) on the tribological and mechanical properties of carbon-nanofiber (CNF)-filled polytetrafluoroethylene (PTFE) composites were studied. Moreover, the influence of various loads (50, 100, 150, and 200 N) and sliding velocities (0.692 and 1.39 m/s) on the friction and wear behaviors of the PTFE composites was investigated. The results showed that the friction coefficients of the PTFE composites decreased initially up to a 0.5 wt % filler concentration and then increased, whereas the antiwear properties of the PTFE composites increased by 1–2 orders of magnitude in comparison with those of pure PTFE. The composite with a 2 wt % filler concentration had the best antiwear properties under all friction conditions. The friction coefficients of the CNF/PTFE composites decreased with increases in the load and sliding velocity, whereas the wear volume loss of the PTFE composites increased. At the same time, the results also indicated that the mechanical properties of the PTFE composites increased first up to a 1 wt % filler concentration and then decreased as the filler concentration was increased above 1 wt %. In comparison with pure PTFE, the impact strength, tensile strength, and elongation to break of the PTFE composites increased by 40, 20, and 70%, respectively, at a 1 wt % filler concentration. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2430–2437, 2007

The tribological behaviors of novel porous Polyetheretherketone (PEEK) composites under 1-hexyl-3-methylimidazolium tetrafluoroborate ionic liquid lubricated condition were investigated. The effect of sliding velocity and applied load on the sweating tribological properties and the stability of lubricating oil film was also studied. Results indicated that when the sliding velocity was 0.69 m/s and the applied load was 250 N, the friction coefficient and wear rate of the ionic liquid lubricated porous sweating activated carbon fiber/polytetrafluoroethene/PEEK composites showed the minimum values, were 0.0197 and 4.145 × 10−15 m3/Nm, respectively. The friction coefficients fluctuated in a narrow range of 0.0162–0.0215. It was found that the porous sweating PEEK composites under ionic liquid lubricated condition showed good low-friction and antiwear performance, especially under the condition of high sliding velocity and applied load. The formed transfer film due to the tribo-chemical reaction as well as boundary lubricating film is effective in improving the carrying capacity and antiwear properties of the porous sweating PEEK composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40989.