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  • 1.
    Abbas, Ghulam
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Johansson, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Alay-e-Abbas, Syed Muhammad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Computational Materials Modeling Laboratory, Department of Physics, Government College University, Faisalabad 38040, Pakistan.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, J. Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Quasi Three-Dimensional Tetragonal SiC Polymorphs as Efficient Anodes for Sodium-Ion Batteries2023In: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 6, no 17, p. 8976-8988Article in journal (Refereed)
    Abstract [en]

    In the present work, we investigate, for the first time, quasi 3D porous tetragonal silicon–carbon polymorphs t(SiC)12 and t(SiC)20 on the basis of first-principles density functional theory calculations. The structural design of these q3-t(SiC)12 and q3-t(SiC)20 polymorphs follows an intuitive rational approach based on armchair nanotubes of a tetragonal SiC monolayer where C–C and Si–Si bonds are arranged in a paired configuration for retaining a 1:1 ratio of the two elements. Our calculations uncover that q3-t(SiC)12 and q3-t(SiC)20 polymorphs are thermally, dynamically, and mechanically stable with this lattice framework. The results demonstrate that the smaller polymorph q3-t(SiC)12 shows a small band gap (∼0.59 eV), while the larger polymorph of q3-t(SiC)20 displays a Dirac nodal line semimetal. Moreover, the 1D channels are favorable for accommodating Na ions with excellent (>300 mAh g–1) reversible theoretical capacities. Thus confirming potential suitability of the two porous polymorphs with an appropriate average voltage and vanishingly small volume change (<6%) as anodes for Na-ion batteries.

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  • 2.
    Berglund, Kim
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Friction and Wear of Self-Lubricating Materials for Hydropower Applications under Different Lubricating Conditions2017In: Lubricants, ISSN 2075-4442, Vol. 5, no 3, article id 24Article in journal (Refereed)
    Abstract [en]

    Self-lubricating bearings in hydropower applications are often lubricated with water under boundary lubricating conditions. Polyhydric alcohols replacing water have shown the potential to reduce both friction and wear. The objective of this work is, therefore, to evaluate the effect of a polyhydric alcohol-based environmentally-acceptable lubricant (EAL) on the friction and wear of self-lubricating materials for conformal contacts under boundary lubricating conditions. The lubricating properties of four commercially-available self-lubricating bearing materials were investigated under three different lubricating conditions: dry, water and a new polyhydric alcohol-based EAL. Bearing materials include one metallic composite and three polymer composites. A reciprocating motion test rig was used to evaluate the wear and friction properties. Surface analysis was performed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and optical profilometry. Results show that the wear rate for the polymer composites is increased when water is present compared to dry operating conditions. The new polyhydric alcohol-based EAL substantially improves both friction and anti-wear performance of all four self-lubricating bearing materials compared to both dry and water conditions. Surface analysis indicates that the material transfer to the counter-surface is limited when the polyhydric alcohol-based EAL is used.

  • 3.
    Berglund, Kim
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Performance of self‐lubricating materials for hydropower applications under different lubricating conditions2016In: Nordic Symposium on Tribology - NORDTRIB 2016, 2016Conference paper (Other academic)
  • 4.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Bair, Scott
    Georgia Institute of Technology, Centre for High Pressure Rheology, G.W. Woodruff School of Mechanical Engineering, Atlanta, GA.
    Mu, Liwen
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Zhu, Jiahua
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Elastohydrodynamic performance of a bio-based, non-corrosive ionic liquid2017In: Applied Sciences, E-ISSN 2076-3417, Vol. 17, no 10, article id 996Article in journal (Refereed)
    Abstract [en]

    To improve performance of machine components, lubrication is one of the most important factors. Especially for use in extreme environments, researchers look for other solutions rather than common lubricant base stocks like mineral oils or vegetable oils. One such example is ionic liquids. Ionic liquids have been defined as molten salts with melting points below 100 °C that are entirely ionic in nature, comprising both cationic and anionic species. The industrial use of ionic liquids is mostly as solvents, electrolytes, extractants and catalysts. In tribological applications, ionic liquids are mainly studied in boundary lubrication and in pure sliding contacts. In this work, the elastohydrodynamic performance of a bio-based, non-corrosive, [choline][L-proline] ionic liquid is evaluated in terms of pressure-viscosity response, film forming capability and friction. The results show a pressure-viscosity coefficient of below 8 GPa-1 at 25 °C, among the lowest reported for any ionic liquid. The ionic liquid generated up to 70% lower friction than a reference paraffin oil with a calculated difference in film thickness of 11%. It was also shown that this ionic liquid is very hygroscopic, which is believed to explain part of the low friction results, but also has to be considered in practical applications since the water content will influence the properties and thus the performance of the lubricant.

  • 5.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Bair, Scott
    Georgia Institute of Technology, Centre for High Pressure Rheology, G.W. Woodruff School of Mechanical Engineering, Atlanta, GA 30332-0405, USA.
    Mu, Liwen
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, OH 44325, USA.
    Zhu, Jiahua
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, OH 44325, USA.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Elastohydrodynamic Performance of a Non-Corrosive Non-Protic Ionic Liquid2017Conference paper (Refereed)
    Abstract [en]

    Ionic liquids have been defined as molten salts with melting points below 100 degrees C that are entirely ionic in nature, comprising both cationic and anionic species. The industrial use of ionic liquids is mostly as solvents, electrolytes, extractants and catalysts. In tribological applications, Ionic liquids are mainly studied in boundary lubrication and in pure sliding contacts. In this work, the elastohydrodynamic performance of a non-corrosive, non-protonic ionic liquid is studied to assess the feasibility to use this kind of ionic liquid in machine components such as gears, rolling bearings and cam followers. This study includes ball on disc friction experiments in rolling sliding full film elastohydrodynamic lubrication at high slide to roll ratios, as well as film thickness measurements with optical interferometry. A commercially available paraffin oil has been used as a reference.

  • 6.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    DLC and Glycerol: Superlubricity in Rolling/Sliding Elastohydrodynamic Lubrication2019In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 67, no 1, article id 23Article in journal (Refereed)
    Abstract [en]

    Low friction is one of the most important parameters for the development of machine components and machines with high efficiency. Many of the common machine components of today such as gears, rolling element bearings and cam-followers are defined by their non-conformal contacts leading to high-contact pressures, typically 1–4 GPa. The lubrication of such contacts is usually called elastohydrodynamic lubrication (EHL). Diamond-like carbon (DLC) coatings and glycerol have individually been shown to produce low friction in boundary, mixed and full film lubrication. A few studies have been conducted using both glycerol and DLC-coated surfaces to achieve even lower friction in pure sliding boundary-lubricated contacts. However, the literature is lacking studies of how the combination of glycerol and DLC performs in non-conformal rolling/sliding contacts where many common machine components operate. Such a study is presented in this article where a ball-on-disc test rig is used to investigate the performance of the combination of DLC and glycerol at pressures up to 1.95 GPa at various entrainment speeds and slide-to-roll ratios. The investigation shows that the DLC-glycerol combination provides very low friction values, in some cases, below the superlubricity threshold of 0.01, possibly shown for the first time at such high pressure in a non-conformal rolling/sliding contact. The low friction mechanism in full film lubrication is a combination of the low pressure-viscosity and high temperature-viscosity sensitivity of glycerol in combination with thermal insulation of the DLC coating and is presented as thermally assisted liquid superlubricity.

  • 7.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Glycerol and Diamond-Like-Carbon in Elastohydrodynamic Lubrication2018Conference paper (Refereed)
  • 8.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Glycerol and DLC in Elastohydrodynamic Lubrication2018In: 73rd STLE Annual Meeting and Exhibition: Program Guide & Schedule, Society of Tribologists and Lubrication Engineers , 2018, p. 46-46Conference paper (Refereed)
    Abstract [en]

    Lubrication and surface engineering plays a vital part in the efficiency of machine components. By using low friction fluids and low friction coatings the efficiency of machine components can be improved dramatically. Glycerol is an example of a fluid with extraordinary low friction characteristics in various systems. Diamond like carbon (DLC) coatings have also been shown to reduce friction in a variety of tribological interfaces. In this study, the elastohydrodynamic performance of glycerol with DLC coated surfaces has been investigated in rolling sliding contacts at high pressures and high slide-to-roll ratios. The DLC-glycerol system is compared to a steel-synthetic oil system and the differences are significant.

  • 9.
    Cao, Danyang
    et al.
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing, PR China.
    Matsakas, Leonidas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Zhang, Jie
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing, PR China.
    Dong, Lisong
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing, PR China.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Zhu, Jiahua
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing, PR China.
    Feng, Xin
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing, PR China.
    Lu, Xiaohua
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing, PR China.
    Mu, Liwen
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing, PR China.
    Biolubricant2023In: Sustainable Production Innovations: Bioremediation and Other Biotechnologies / [ed] Alok Kumar Patel; Amit Kumar Sharma, John Wiley & Sons, 2023, p. 1-56Chapter in book (Other academic)
  • 10.
    Chen, Jun
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A mini-review: the ice resistance durability and mechanical durability of ice-phobic surfacesManuscript (preprint) (Other academic)
  • 11.
    Chen, Jun
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of anti-icing coating functional groups on ice adhesion2024In: Applied materials today, ISSN 2352-9407, Vol. 39, article id 102264Article in journal (Refereed)
    Abstract [en]

    Unwanted ice build-up is a ubiquitous phenomenon in nature, which creates a series of catastrophic impacts on a wide range of human activities. Various anti/de-icing materials have been proposed for dealing with icing issues. Superhydrophobic anti/de-icing coatings have been widely reported since it has high efficiency and can be achieved in different ways. The surface functional groups have a significant influence on surface energy which is related to surface wettability. However, the influence of the coating surfaces functional groups on the anti-/de-icing properties is still not well studied. To investigate this influence, different groups with different hydrophilicity have been introduced to 3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyl acrylate (TFOA) to fabricate several branch copolymer ice-phobic coatings. The anti-icing performance and the influence of group radius and interaction were studied. The acrylic acid TFOA showed a great superhydrophobic property (over 150° water contact angle), lower ice adhesion strength (<50 kPa), and lower wear depth compared with other copolymer coatings. The mechanism was studied via the molecular dynamic calculation carried out in ChemDraw software. The interaction between hydrophobic and hydrophilic groups and the steric length of the hydrophilic groups influence the surface structure and surface element distribution, further influencing the ice adhesion strength.

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  • 12.
    Chen, Jun
    et al.
    College of Science, Nanjing Forestry University, Nanjing, P. R. China .
    Li, Fanzhu
    Key Lab Beijing City Preparat & Proc Novel Polyme, State Key Lab Organ Inorgan Composites, Beijing University of Chemical Technology, Beijing, P. R. China.
    Luo, Yanlong
    College of Science, Nanjing Forestry University, Nanjing, P. R. China .
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ma, Xiaofeng
    College of Science, Nanjing Forestry University, Nanjing, P. R. China .
    Zhang, Meng
    Institute of Chemical Industry of Forestry Products, CAF, Nanjing, P. R. China.
    Boukhvalov, D. W.
    College of Science, Nanjing Forestry University, Nanjing, P. R. China.
    Luo, Zhenyang
    College of Science, Nanjing Forestry University, Nanjing, P. R. China.
    A self-healing elastomer based on an intrinsic non-covalent cross-linking mechanism2019In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, no 25, p. 15207-15214Article in journal (Refereed)
    Abstract [en]

    Synthesis and comprehensive examination of a polyurethane (urea) elastomer that self-heals based on intrinsic dynamic non-covalent bonds (van der Waals and hydrogen) are reported. The dynamic non-covalent bonds include hydrogen bonds and van der Waals forces. The difference in the previous approach in which hydrogen bond self-healing materials introduced dense quadruple hydrogen bonds at the ends or branched chains poly(propylene carbonate) (PPC) diol was used as the soft segment of the polyurethane (urea) material, and strong van der Waals forces were provided by the large number of carbonyl groups in its main chain; hydrogen bonds were formed by urethane bonds, urea bonds, and the carbonyl groups on PPC. The mechanical properties and healing efficiency of the self-healing polyurethane (urea) elastomer were studied. In situtemperature-dependent infrared and low-field nuclear magnetic resonance (LNMR) measurements were combined with molecular dynamics simulations to investigate the self-healing mechanisms. The results of the studies on the self-healing polyurethane demonstrate that the dynamic cross-linking between hydrogen bonds and van der Waals forces is the basic driving force for the self-healing ability of the material, and temperature is the key factor that affects hydrogen bonding and van der Waals forces. The effect of crystallization on the self-healing ability of the material was also studied. The molecular dynamics simulation results also demonstrate interplay between van der Waals forces and hydrogen bonds at different temperatures.

  • 13.
    Chen, Jun
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Luo, Zhenyang
    College of Science, Nanjing Forestry University, Nanjing 210037, P. R. China.
    An, Rong
    Herbert Gleiter Institute of Nanoscience, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210037, P. R. China.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Novel Intrinsic Self-Healing Poly-Silicone-Urea with Super-Low Ice Adhesion Strength2022In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 18, no 22, article id 2200532Article in journal (Refereed)
    Abstract [en]

    Accumulation of snow and ice often causes problems and even dangerous situations for both industry and the general population. Passive de-icing technologies, e.g., hydrophobic, liquid-infused bionic surfaces, have attracted more and more attention compared with active de-icing technologies, e.g., electric heating, hot air heating, due to the passive de-icing technology's lower energy consumption and sustainability footprint. Using passive de-icing coatings seems to be one of the most promising solutions. However, the previously reported de-icing coatings suffer from high ice adhesion strength or short service life caused by wear. An intrinsic self-healing material based on poly-silicone-urea is developed in this work to address these problems. The material is prepared by introducing dynamic disulfide bonds into the hard phase of the polymer. Experimental results indicate that this poly-silicone-urea has a self-healing efficiency of close to 99%. More interestingly, it is found that the coating prepared from this poly-silicone-urea has a super low ice adhesion force, only 7 ± 1 kPa, which is almost the lowest value compared with previous intrinsic self-healing de-/anti-icing reports. This material can maintain low ice adhesion strength after healing. This intrinsic self-healing poly-silicone-urea can meet several practical applications, opening the door for future sustainable anti-/de-icing technologies.

  • 14.
    Chen, Jun
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    In-situ polymerized siloxane urea enhanced graphene-based super-fast, durable, all-weather elec-photo-thermal anti-/de-icing coating2023In: Journal of Science: Advanced Materials and Devices, ISSN 2468-2284, Vol. 8, no 3, article id 100604Article in journal (Refereed)
    Abstract [en]

    Previous investigations on anti-/de-icing techniques have primarily focused on mild laboratory conditions, which have limited practical applicability due to their short service life. Consequently, there is an urgent demand for the development of durable anti-/de-icing technologies capable of withstanding complex environmental conditions. In this research endeavour, we have successfully formulated a hydrophobic coating based on graphene. To circumvent the challenges associated with environmentally unfriendly organic solvents, we utilized a graphene water slurry as the foundational material and subsequently incorporated a poly (vinyl alcohol)-water solution. The resulting solution was subjected to in situ polymerization of a siloxane urea crosslinked polymer, yielding the desired coating solution. Following a solution spraying and drying process, the ultimate product obtained was the hydrophobic conductive graphene (HCG) siloxane Coating. The HCG siloxane Coating exhibits a conductivity of 66 S/m, enabling it to melt ice droplets within a mere 10 s, whereas conventional coatings require 20–500 s for the same task. A comprehensive field test conducted during an entire winter period on a high mountain situated within the Arctic Circle in Finland demonstrated the excellent anti-icing properties of the developed coating when subjected to approximately 310 W/m2 power. Furthermore, the coating exhibited satisfactory de-icing performance under approximately 570 W/m2 power, successfully removing ice accumulations within approximately 10 min. Throughout the field test, temperatures frequently plummeted to −20 °C, accompanied by wind speeds reaching up to 12 m/s. Material characterization revealed that the micro-nano structure of the coating surface, which engenders favourable hydrophobic behaviour, was primarily attributed to the phase separation resulting from hydrophilic and hydrophobic interactions. Moreover, the semi-interpenetrating structure formed by the polyvinyl alcohol molecular chains and in-situ polymerized siloxane urea ensured the coating's strength.

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  • 15.
    Chen, Jun
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Parsi, Pranay Kumar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Graphene-enhanced, wear-resistant and thermal-conductive, anti-/de-icing Gelcoat composite coating2024In: Advanced Composites and Hybrid Materials, ISSN 2522-0128, Vol. 7, no 1, article id 9Article in journal (Refereed)
    Abstract [en]

    Wind power is considered as a sustainable and environmentally friendly energy source. However, the occurrence of icing poses significant challenges to energy production, particularly in frigid regions during the winter season. Conventional strategies employed for preventing and removing ice formation have proven inadequate due to their inability to satisfy intricate requirements or their high energy consumption. In this study, a commercial gelcoat coating was adopted as an anti-/de-icing coating by introducing different concentrations of graphene and boron nitride into the gelcoat coating through physical mixing. Extensive investigations were conducted on the correlation between anti-/de-icing, wear resistance, and thermal conductivity. Notably, the incorporation of nanoparticles induced a rise in the surface roughness, resulting in prolonged resistance to water icing on the coated surface. The wear resistance and thermal conductivity of the composite coating were enhanced through the inclusion of boron nitride and graphene. The building of thermal conductive particle networks improved thermal conductivity which can lead to improved heat transfer and heat distribution. At the same time, the enhanced gelcoat composite coating exhibited exceptional passive anti-/de-icing performance and wear resistance. This coating can replace commercial coatings to improve anti-/de-icing efficiency for the existing active heating anti-/de-icing techniques available in the market.

    In this study, we aimed to enhance the wear resistance, thermal conductivity, and anti-/de-icing properties of a gelcoat composite coating by incorporating graphene and boron nitride. The gelcoat graphene coating showed better performance than the gelcoat boron nitride coating and pure gelcoat coating. The improved wear resistance of the gelcoat graphene coating can be attributed to the two-dimensional layer structure of graphene, while the addition of graphene resulted in a threefold increase in the thermal conductivity of the gelcoat composite coating compared to the pure gelcoat coating. The gelcoat composite coatings exhibited a high-water contact angle and low ice adhesive force. It was observed that as the surface roughness increased, the water contact angle also increased. The increase in ice adhesion after abrasion proves that abrasion is always detrimental to de-icing. Despite the extension of icing delay time, the large number of grooves and bumps created by wear results in stronger mechanical interlocking. It is worth mentioning that gelcoat graphene coating still demonstrated lower ice adhesive strength than gelcoat boron nitride coating and pure gelcoat coating. Overall, we successfully developed a gelcoat graphene coating with improved thermal conductivity, wear resistance, and low ice adhesive properties. This novel composite coating has the potential to significantly enhance the efficiency of existing heating technologies for anti-/de-icing applications, thereby reducing energy consumption associated with the turbine blades’ anti-/de-icing system.

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  • 16.
    Chen, Long
    et al.
    Department of Chemical and Biomolecular Engineering, The University of Akron, Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Ji, Tuo
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Mu, Liwen
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Brisbin, Logan
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Guo, Zhanhu
    Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville.
    Khan, Mohammel A.
    Department of Physics and Astronomy, Louisiana State University, Baton Rouge.
    Young, David P.
    Department of Physics and Astronomy, Louisiana State University, Baton Rouge.
    Zhu, Jiahua
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Facile synthesis of mesoporous carbon nanocomposites from natural biomass for efficient dye adsorption and selective heavy metal removal2016In: RSC Advances, E-ISSN 2046-2069, Vol. 6, no 3, p. 2259-2269Article in journal (Refereed)
    Abstract [en]

    Mesoporous carbon with embedded iron carbide nanoparticles was successfully synthesized via a facile impregnation–carbonization method. A green biomass resource, cotton fabric, was used as a carbon precursor and an iron precursor was implanted to create mesopores through a catalytic graphitization reaction. The pore structure of the nanocomposites can be tuned by adjusting the iron precursor loadings and the embedded iron carbide nanoparticles serve as an active component for magnetic separation after adsorption. The microstructure of the nanocomposites was carefully investigated by various characterization techniques including electron microscopy, X-ray diffraction, surface analyzer, magnetic property analyzer and etc. The newly created mesopores are demonstrated as a critical component to enhance the adsorption capacity of organic dyes and embedded iron carbide nanoparticles are responsible for the selective removal of heavy metal ions (Zn2+, Cu2+, Ni2+, Cr6+ and Pb2+). Isotherm adsorption, kinetic study at three different temperatures (25, 45 and 65 °C) and cycling retention tests were performed to understand the adsorptive behavior of the nanocomposites with organic dyes (methylene blue and methyl orange). Together with the preferable removal of more toxic heavy metal species (Cr6+ and Pb2+), these mesoporous nanocomposites show promising applications in pollutant removal from water. The facile material preparation allows convenient scale-up manufacturing with low cost and minimum environmental impact.

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  • 17.
    Chen, Long
    et al.
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Ji, Tuo
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Mu, Liwen
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Wang, Huaiyuan
    College of Chemistry and Chemical Engineering, Northeast Petroleum University, Daqing.
    Zhu, Jiahua
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Pore size dependent molecular adsorption of cationic dye in biomass derived hierarchically porous carbon2017In: Journal of Environmental Management, ISSN 0301-4797, E-ISSN 1095-8630, Vol. 196, p. 168-177Article in journal (Refereed)
    Abstract [en]

    Hierarchically porous carbon adsorbents were successfully fabricated from different biomass resources (softwood, hardwood, bamboo and cotton) by a facile two-step process, i.e. carbonization in nitrogen and thermal oxidation in air. Without involving any toxic/corrosive chemicals, large surface area of up to 890 m2/g was achieved, which is comparable to commercial activated carbon. The porous carbons with various surface area and pore size were used as adsorbents to investigate the pore size dependent adsorption phenomenon. Based on the density functional theory, effective (E-SSA) and ineffective surface area (InE-SSA) was calculated considering the geometry of used probing adsorbate. It was demonstrated that the adsorption capacity strongly depends on E-SSA instead of total surface area. Moreover, a regression model was developed to quantify the adsorption capacities contributed from E-SSA and InE-SSA, respectively. The applicability of this model has been verified by satisfactory prediction results on porous carbons prepared in this work as well as commercial activated carbon. Revealing the pore size dependent adsorption behavior in these biomass derived porous carbon adsorbents will help to design more effective materials (either from biomass or other carbon resources) targeting to specific adsorption applications.

  • 18.
    Dhakal, Nayan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological behaviour of UHMWPE composites lubricated by polyvinylpyrrolidone‐modified water2022In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 34, no 1, p. 42-53Article in journal (Refereed)
    Abstract [en]

    Tribological characteristics of ultra-high molecular weight polyethylene (UHMWPE) composites with 10% short carbon fibres (SCF) lubricated in water with polyvinylpyrrolidone (PVP) as a modifier were investigated. The aqueous solutions with varying concentrations of PVP were prepared, and their viscosity-enhancing action, friction-reducing properties and anti-wear performances were studied under different loading conditions equivalent to 10 and 20 MPa of contact pressures at a constant sliding speed of 20 mm/s. The results showed that PVP is an excellent viscosity modifier for water. PVP-modified water exhibited excellent performance compared to distilled water, reducing the wear and friction coefficient of neat UHMWPE up to 25%. The anti-wear properties of UHMWPE-SCF composite were also improved with PVP modified water lubrication, yielding a maximum reduction of wear up to 45%. PVP seems to be a promising additive of modifying the lubricating properties of distilled water for water-based lubrication. 

  • 19.
    Fisher, Trevor R.
    et al.
    School of Chemical, Biological and Materials Engineering, University of Oklahoma, Norman, Oklahoma, US.
    Zhou, Guobing
    School of Chemical, Biological and Materials Engineering, University of Oklahoma, Norman, Oklahoma, US.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Huang, Liangliang
    School of Chemical, Biological and Materials Engineering, University of Oklahoma, Norman, Oklahoma, US.
    How does hydrogen bond network analysis reveal the golden ratio of water–glycerol mixtures?2020In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 22, no 5, p. 2887-2907Article in journal (Refereed)
    Abstract [en]

    Properties of water–glycerol mixtures depend closely on the water/glycerol ratio. Around the 30 mol% glycerol concentration mark, the so-called golden ratio of water–glycerol mixtures, several of the mixture's properties have observed maxima or minima, without a clear fundamental explanation. In this work, a series of molecular dynamics simulations have been performed over a wide range of water–glycerol concentrations to analyze the intermolecular hydrogen bond (H-bond) network. The collected values from simulations are justified from both a probabilistic model of H-bonding and from observing the dynamic behavior of each type of H-bonds. The populations of H-bonds that exist at a given concentration of glycerol are largely governed by the probability of one oxygen atom randomly associating with another oxygen atom. However, the H-bonds that glycerol oxygen can form are dependent on the H-bonds that are formed by the other intramolecular glycerol oxygen. Based on the dynamic analysis of each type of H-bonds, there are deviations from randomly associating with another oxygen. Water preferentially donates a hydrogen to a glycerol than to another water molecule. Yet, glycerol has a near-equal likelihood for donating a hydrogen to either another glycerol or a water. This has an effect of increasing the number of H-bonds between water and glycerol molecules and decreasing H-bonds between two water molecules. A maximum contribution of H-bonds between water and glycerol occurs around 30 mol% glycerol which is a concentration where several of the mixture's properties have an observed maxima or minima.

  • 20.
    Hua, Jing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A smart friction control strategy enabled by CO2 absorption and desorption2019In: Scientific Reports, E-ISSN 2045-2322, Vol. 9, no 1, article id 13262Article in journal (Refereed)
    Abstract [en]

    Intelligent control of friction is an attractive but challenging topic and it has rarely been investigated for full size engineering applications. In this work, it is instigated if it would be possible to adjust friction by controlling viscosity in a lubricated contact. By exploiting the ability to adjust the viscosity of the switchable ionic liquids, 1,8-Diazabicyclo (5.4.0) undec-7-ene (DBU)/ glycerol mixture via the addition of CO2, the friction could be controlled in the elastohydrodynamic lubrication (EHL) regime. The friction decreased with increasing the amount of CO2 to the lubricant and increased after partial releasing CO2. As CO2 was absorbed by the liquid, the viscosity of the liquid increased which resulted in that the film thickness increased. At the same time the pressure-viscosity coefficient decreased with the addition of CO2. When CO2 was released again the friction increased and it was thus possible to control friction by adding or removing CO2.

  • 21.
    Hua, Jing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Controllable Friction of Green Ionic Liquids via Environmental Humidity2020In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. 22, no 5, article id 1901253Article in journal (Refereed)
    Abstract [en]

    Intelligent control of friction is an attractive but challenging topic. In this work, it is investigated if it would be possible to adjust friction in a lubricated contact by controlling environmental humidity. By exploiting the ability to adjust the environmental humidity by various saturated salt solutions, friction behavior of contacts lubricated with Choline l‐Proline ([Cho][Pro]) is modulated in a wide range of relative humidity (RH). The friction increases when the environmental humidity is increased and decreases when water is partially evaporated to a lower RH. It is thus possible to control friction by environmental humidity. The addition of water in ionic liquids (ILs) causes a decrease in viscosity, but as the tests are calculated to be performed in boundary lubrication the viscosity change is not the main factor for the change in friction. The friction sensitivity of RH can be explained by the effect of adhesion on the water uptake from humid air by [Cho][Pro]. Furthermore, the reversible changes of H‐bond types determined by the water content could be another explanation to the altered friction.

  • 22.
    Hua, Jing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Controllable superlubricity achieved with mixtures of green ionic liquid and glycerol aqueous solution via humidity2022In: Journal of Molecular Liquids, ISSN 0167-7322, E-ISSN 1873-3166, Vol. 345, article id 117860Article in journal (Refereed)
    Abstract [en]

    In this work, superlubricity between steel surfaces lubricated by mixtures of [Choline][Proline] ([Cho][Pro]) ionic liquid and glycerol aqueous solution has been reached by using a rotating tribometer. Stable superlubricity could be obtained even under the humidity between 7 to 9% RH. The lowest friction is observed when the lubricant contains 3 wt.% ionic liquid. It is found that adding 3 wt.% [Cho][Pro] is helpful to maintain enough water in the steady period to retain a low viscosity. According to the calculation, the superlubricity achieved in thin film lubrication region, which is attributed to the stern layer formed by [Cho][Pro] and hydrogen-bond network that enabled a thin water layer at the interface. Interestingly, it is observed that humidity can be used to control lubrication state between superlubricity and non-superlubricity. This study provides a new method to accomplish switchable superlubricity under low humidity.

  • 23.
    Hua, Jing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Controlling friction in Ionic Liquid/Glycerol Aqueous Solution lubricated contacts by adjusting CO2 and water content2021In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 161, article id 107070Article in journal (Refereed)
    Abstract [en]

    Nowadays, the awareness for the importance of green lubricants and green lubricating additives is increasing. In this work, [Choline][Proline] ([Cho][Pro]) was added into glycerol aqueous solution to receive a high-performance green lubricant. The effect of environment condition, e.g., CO2 and water, on the green lubricant was studied. It is found that the properties of the green lubricant could be modulated by CO2 and water content. As CO2 was absorbed by the liquid, the viscosity of the liquid increased, while the viscosity of liquid diminished after adding more water. The presence of CO2 led to an obvious increase of friction. At the same time, it is also found that the friction could be altered by water content. Thus, it is possible to control friction by changing CO2 and water content.

  • 24.
    Hua, Jing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Friction Control of Chitosan-Ag Hydrogel by Silver Ion2022In: ES Materials & Manufacturing, ISSN 2578-0611, Vol. 16, p. 30-36Article in journal (Refereed)
    Abstract [en]

    The tunable friction behavior of Chitosan (CS)-Ag hydrogel enabled by altering metal ions is evaluated. Friction control could be achieved under boundary lubrication. When adding Ag+ into a CS solution, the formed gel provided lower friction. The difference in friction coefficient between the two phases can be reversibly switched by adding Cl- or excessive Ag+ ions. It also can be found that the gel phased lubricant has a better anti-wear ability under boundary lubrication conditions. Both solution and gel typed lubricants could achieve superlubricity under elastohydrodynamic lubrication. The switchable and tunable frictional hydrogels can extend the application in the design of smart control equipment.

  • 25.
    Hua, Jing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Non-corrosive Green Lubricant With Dissolved Lignin in Ionic Liquids Behave as Ideal Lubricants for Steel-DLC Applications2019In: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 7, article id 857Article in journal (Refereed)
    Abstract [en]

    Diamond-like carbon (DLC)–steel contacts become more and more popular in the industry now. Since the surface chemical properties of DLC are quite different from those of iron, traditional formulated lubricants have problems to form tribo-chemical films, which are effective to improve the tribological performance for steel-steel contacts, on the surface of DLC. Thus, new lubricants formulation strategies are needed to be considered for steel-DLC applications. A kind of green lubricant (lignin-[Choline][L-Proline] (L-[CH][Pro])) without any traditional tribo-chemical active element, i.e., free of P, S, B, etc., was studied in this paper for the steel-DLC contact. To find the difference between this new ILs and the traditional lubricants, a commercially available fully formulated lubricant was used as a reference. An Optimol SRV-III oscillating friction and wear tester was used to evaluate the tribological performance. Three different kinds of commercially available DLC coatings (Tribobond 40(Cr + a-C:H:W), Tribobond 43 [(Cr+) a-C:H), and Tribobond 44(a-C:Cr)] were investigated. The results show that the ILs exhibit an obviously lower friction coefficient than that of the traditional commercially available fully formulated lubricant. Among those three DLC coatings, the (Cr+) a-C:H DLC coating exhibits the biggest improvement of wear resistance lubricated with the new ILs than that of the commercially available fully formulated lubricant. It's expected that its excellent tribological properties are attributed to the affinity of the ILs to the metal surface and the strength of the ionic liquids interactions by hydrogen bonding. Thus, forming strong physical adsorption strategy, instead of forming chemical tribo-films, is recommended to enhance the lubricating performance of lubricants for DLC.

  • 26.
    Huang, Xianzhu
    et al.
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing .
    Wu, Jian
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lu, Xiaohua
    Key Laboratory of Material and Chemical Engineering, Nanjing Tech University, Nanjing .
    Feng, Xin
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing .
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological Properties of Porous PEEK Composites Containing Ionic Liquid under Dry Friction Condition2017In: Lubricants, ISSN 2075-4442, Vol. 5, no 2, article id 19Article in journal (Refereed)
    Abstract [en]

    NaCl particles were added into Polyetheretherketone (PEEK) and its composites to produce porous PEEK-based materials by washing NaCl away after the high-temperature compression molding process. After that, an ionic liquid was added into the porous materials under vacuum condition. Carbon fibers (CF), as reinforcement, and PTFE, as an internal solid lubricant, were employed to prepare PEEK composites. Tribological properties under dry friction condition were studied on a ring-on-disc tribo-meter. The influence of CF and PTFE on tribological properties was carefully investigated. The results indicated that, in comparison with traditional PEEK composites (CF/PTFE/PEEK), the porous PEEK composites containing ionic liquid showed much better tribological properties. It is found that CF can help PEEK form effective pores to suck in the ionic liquid resulting in a better tribological performance. CF reinforced porous PEEK containing ionic liquid (p-CF/PEEK + IL) demonstrated the lowest friction coefficient (27% of CF/PTFE/PEEK) and the lowest wear loss (only 0.9% of CF/PTFE/PEEK). Long time tribological test revealed that the wear mass loss comes from the running-in period, while its wear is negligible after this period. It is also found that the addition of PTFE has a negative influence on the tribological behaviors, especially under high sliding velocity and applied load

  • 27.
    Ji, Tuo
    et al.
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Chen, Long
    Department of Chemical and Biomolecular Engineering, The University of Akron, Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Mu, Liwen
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Yuan, Ruixia
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Knoblauch, Michael
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Bao, Forrest Sheng
    College of Chemistry and Chemical Engineering, Northeast Petroleum University, Daqing.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Wang, Huaiyan
    Department of Electrical and Computer Engineering, The University of Akron.
    Zhu, Jiahua
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Green Processing of Plant Biomass into Mesoporous Carbon as Catalyst Support2016In: Chemical Engineering Journal, ISSN 1385-8947, E-ISSN 1873-3212, Vol. 295, p. 301-308Article in journal (Refereed)
    Abstract [en]

    Four different plant biomass, bamboo, cotton, soft wood and hard wood, were utilized as carbon precursors to fabricate porous carbon catalyst supports via a chemical free approach. Large surface area with unique mesoporous structure was successfully created in the carbon, which made them suitable for catalyst support. After decorating silver nanoparticles onto these carbon supports, nitroaromatics reduction reactions were performed to evaluate the catalyst activity. Results indicate that chemical composition and surface groups of carbon supports determine the metal catalyst nucleation/growth while the porous microstructure of support affects the mass transport of reactant/product across the liquid/catalyst interface. Among the four selected biomass, porous carbon manufactured from soft wood acquires the highest average pore size, pore volume, mesopore volume fraction and best catalytic activity after decorating silver nanoparticles. This work not only presents an environmental benign process that converts natural biomass into effective porous carbon catalyst supports, but also offers a comprehensive understanding of biomass structure/composition relating to their suitability as catalyst support.

  • 28.
    Johansson, Pontus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Elo, Robin
    Ångström Tribomaterials Group, Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Fadaei Naeini, Vahid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Insights of the Ultralow Wear and Low Friction of Carbon Fiber Reinforced PTFE in Inert Trace Moisture Environment2023In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 71, no 3, article id 100Article in journal (Refereed)
    Abstract [en]

    Ultralow wear rates and low friction have been observed for carbon fiber reinforced PTFE (CF/PTFE) when sliding against steel or cast iron in dry gas environments. Although the strong environmental sensitivity of this tribosystem is well known, the origin of the outstanding tribological performance in dry gas remains unanswered. Some researchers attribute the low friction and wear to the formation of carbon-rich surfaces in the absence of oxygen and moisture in the environment. However, low friction between carbon surfaces is generally dependent on moisture. In this paper, extensive analyzes are conducted on the tribofilms formed on the CF/PTFE surface and the steel counterface after sliding in a high-purity nitrogen environment. TEM analysis of a cross-section of the tribofilm on the steel surface reveals that the sliding surface consists mainly of iron (II) fluoride and not carbon, even though a significant amount of carbon was observed near the surface. XPS and TEM analysis further revealed that the tribofilm formed on the worn composite surface consisted of nanoparticle agglomerates, anchored to the PTFE matrix and to each other by carbon with turbostratic structure. Turbostratic carbon also formed an ultrathin and surface-oriented superficial layer on top of the agglomerates. Governing mechanisms of the low friction and wear of the CF/PTFE—steel tribosystem were investigated by complementary tribotests with pure graphite samples and MD simulations of the identified surfaces. These indicated that the low friction between the carbon and iron fluoride in the tribofilms is due to poor adhesion between the distinctly different surfaces.

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  • 29.
    Johansson, Pontus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of humidity and counterface material on the friction and wear of carbon fiber reinforced PTFE composites2021In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 157, article id 106869Article in journal (Refereed)
    Abstract [en]

    The tribological performance of PTFE composites is affected by both the composition of the counterface material and the sliding environment. However, no comprehensive investigation has been conducted on the combined effect of the humidity and counterface material on PTFE composites. This study investigates the tribological behavior of carbon fiber reinforced PTFE composites sliding in a dry nitrogen environment at different humidity levels. Experiments were conducted in an enclosed tri-pin-on-disc tribometer against two different metallic counterface materials. Tests in laboratory air were used for comparison. Results indicate that the tribological performance of carbon fiber reinforced PTFE composites are sensitive to environmental changes. The impact of humidity on both the coefficient of friction and specific wear rate was up to about 40%.

  • 30.
    Johansson, Pontus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of Oxygen and Moisture on the Friction and Wear of Carbon Fiber-Reinforced Polymers2023In: Lubricants, ISSN 2075-4442, Vol. 11, no 9, article id 412Article in journal (Refereed)
    Abstract [en]

    Carbon fiber-reinforced polytetrafluoroethylene (CF/PTFE) composites are frequently used in tribological dry gas applications, such as in dynamic seals in reciprocating hydrogen gas compressors and Stirling engines, due to their superior friction and wear. Due to the increasing concerns regarding fluoropolymers as possible pollutants of harmful per- and poly-fluoroalkyl substances (PFAS) emissions, replacements for PTFE should be investigated. The literature indicates that CF-reinforced polyetheretherketone (CF/PEEK) may have similar favorable tribological properties to CF/PTFE. However, the tribological behavior of CF/PEEK in dry gas is poorly understood, and no direct comparison has been made between the two materials. The aim of this study was to compare the effect of oxygen and moisture on the friction and wear of CF/PTFE and CF/PEEK. Tribological tests were carried out with a tri-pin-on-disc tribometer in a nitrogen environment with individually controlled contents of oxygen and moisture. The results showed that the effect of oxygen and moisture are distinctly different for CF/PTFE and CF/PEEK. While CF/PTFE performs best in oxygen-deficient environments, CF/PEEK performs best in moisture-enriched environments. Complementary tests with a PTFE composite filled with both CF and PEEK suggested that the environmental sensitivity can be significantly reduced by combining the two polymers.

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  • 31.
    Johansson, Pontus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of roughness on the running-in behavior and tribofilm formation of carbon fiber reinforced PTFE composite in trace moisture environment2022In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 500-501, article id 204367Article in journal (Refereed)
    Abstract [en]

    Counterface roughness is known to affect the tribological behavior of carbon fiber reinforced PTFE. However, the effect of roughness in trace moisture environments has not yet been extensively investigated. In this study, the tribological behavior and tribofilm formation were evaluated for a carbon fiber reinforced PTFE composite sliding in a trace moisture environment against 34CrNiMo6 steel counterfaces with different roughness. Tribotests were conducted with a three-pin-on-disc tribometer at a sliding velocity of 2.2 m/s and in a nitrogen environment with moisture content controlled to 11 ppm. Generally, smoother counterfaces gave lower wear, both during running-in and steady-state. Contrarily, the coefficient of friction was only affected by roughness during running-in. Surface analysis from different stages of running-in were done to elucidate the formation of tribofilms and their different characteristics. For the rough countersurface, a loosely adhered transfer film is transitionally formed at the beginning of sliding to enable the formation of a persistent transfer film. Contrarily, for the case of a smooth countersurface, the formation of a persistent transfer film is initiated from the start. Similarly for the rough and smooth countersurface, a micrometer thick tribofilm with excellent low friction properties is observed on the PTFE composite after running-in.

  • 32.
    Johansson, Pontus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mechanisms behind the environmental sensitivity of carbon fiber reinforced polytetrafluoroethylene (PTFE)2024In: Friction, ISSN 2223-7690, E-ISSN 2223-7704, Vol. 12, no 5, p. 997-1015Article in journal (Refereed)
    Abstract [en]

    Carbon fiber reinforced polytetrafluoroethylene (CF/PTFE) composites are known for their exceptional tribological performance when sliding against steel or cast iron in inert gas environments. Compared to experiments in humid air, about an order of magnitude lower wear rate and several times lower coefficient of friction have been reported for tests conducted in dry nitrogen and hydrogen. Moreover, trace moisture has been shown to affect the friction and wear significantly of this tribosystem, although a possible effect of oxygen cannot be ruled out due to uncertainties regarding the oxygen concentrations. While several studies have pointed out the environmental sensitivity of CF/PTFE, the understanding of the underlying mechanisms are very limited. The objective of this research is to investigate the individual and combined effect of oxygen and moisture on the tribological behavior of CF/PTFE sliding against steel. Additionally, this study aims to elucidate the underlying mechanisms that govern the environmental sensitivity of the system. Climate-controlled three-pin-on-disc experiments were conducted in nitrogen atmospheres at various concentrations of oxygen and moisture. The tribological results clearly demonstrate that both moisture and oxygen contribute to increased friction and wear. However, the adverse effect was much more pronounced for oxygen than moisture. A qualitative method was developed to estimate the tribofilm coverage on the CF/PTFE surface. Results showed strong correlation between high coverage of strongly adhered tribofilm and low wear rate. Moreover, a loosely adhered tribofilm was observed on top of the CF/PTFE surface in presence of moisture. FTIR analysis indicated that the loosely adhered tribofilm found in the moisture-enriched environment contained a significant amount of adsorbed water, which may explain the lower coefficient of friction in presence of moisture compared to oxygen. The adsorbed water in the loosely adhered tribofilm could be an indication of moisture-driven lubrication by the non-graphitic carbon in the tribofilm.

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  • 33.
    Lan, Xiaoyu
    et al.
    College of Science, Nanjing Forestry University, Nanjing, P. R. China.
    Ma, Xiaofeng
    College of Science, Nanjing Forestry University, Nanjing, P. R. China.
    Wang, Lei
    College of Science, Nanjing Forestry University, Nanjing, P. R. China.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gu, Qun
    Department of Chemistry, Edinboro University of Pennsylvania, Edinboro, United States.
    Wu, Linlin
    College of Materials Science and Engineering, Nanjing Tech University, Nanjing, P. R. China.
    Gu, Xiaoli
    College of Chemical Engineering, Nanjing Forestry University, Nanjing, P. R. China.
    Luo, Zhenyang
    College of Science, Nanjing Forestry University, Nanjing , P. R. China.
    Self-Assembly of Diblock Copolymers Containing Thermo- and Photoresponsive Lower Critical Solution Temperature Phase Behavior Polymer with Tunable Assembly Temperature in an Ionic Liquid Mixture2019In: ACS Omega, E-ISSN 2470-1343, Vol. 4, no 6, p. 11229-11236Article in journal (Refereed)
    Abstract [en]

    This work prepared a type of diblock copolymer with thermo- and photosensitivity in ionic liquids (ILs). P(N,N-dimethylacrylamide) (compatible with ILs) was prepared as one segment, while butyl acrylate (BA) and 4-phenylazophenylmethacrylate (AzoMA) were copolymerized as another segment P(AzoMA-r-BA) with stimuli responsiveness. The diblock copolymer showed tunable lower critical micellization temperature (LCMT) in two mixed imidazole ionic liquids. The value of LCMT depends on not only the conformation status of the azo group in copolymers but also the azo group content in copolymers and mixed ratio of ionic liquids. Based on this tunable LCMT, photoinduced micellization/demicellization can be achieved near room temperature by alternate irradiation with visible and ultraviolet light, and it is totally reversible.

  • 34.
    Li, Ruiyun
    et al.
    State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical Physics Chinese Academy of Science Lanzhou 70000 China; Institute of Materials Science and Engineering Lanzhou University Lanzhou 730000 China.
    Yang, Xing
    State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical Physics Chinese Academy of Science Lanzhou 70000 China.
    Zhao, Jun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Yue, Chengtao
    School of Nuclear Science and Technology University of South China Hengyang 421001 China.
    Wang, Yongfu
    State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical Physics Chinese Academy of Science Lanzhou 70000 China.
    Li, Jiangong
    Institute of Materials Science and Engineering Lanzhou University Lanzhou 730000 China.
    Meyer, Ernst
    Department of Physics University of Basel Klingelbergstrasse 82 Basel 4056 Switzerland.
    Zhang, Junyan
    State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical Physics Chinese Academy of Science Lanzhou 70000 China;Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of Sciences Beijing 100049 China.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Operando Formation of Van der Waals Heterostructures for Achieving Macroscale Superlubricity on Engineering Rough and Worn Surfaces2022In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 32, no 18, article id 2111365Article in journal (Refereed)
    Abstract [en]

    Macroscale superlubricity breakdown of lubricating materials caused by substrate surface roughening and mechanochemical modification poses great challenges for their practical tribological applications. Here, a facile way is reported to access robust macroscale superlubricity in a vacuum environment, via the operando formation of graphene/transition-metal dichalcogenide (TMDC) heterostructures at wear-induced rough surfaces. By trapping active amorphous carbon (a-C) wear products between TMDC flakes, the sandwich structures readily transform into graphene/TMDC heterostructures during running-in stage, based on shear-induced confinement and load-driven graphitization effects. Then they assemble into multipoint flake-like tribofilms to achieve macroscale superlubricity at steady stage by reducing contact area, eliminating strong cross-interface carbon–carbon interactions and polishing a-C rough nascent surface. Atomistic simulations reveal the preferential formation of graphene/TMDC heterostructures during running-in stage and demonstrate the superlubric sliding of TMDCs on the graphene. The findings are of importance to achieve robust superlubricity and provide a good strategy for the synthesis of other van der Waals heterostructures.

  • 35.
    Li, Yiling
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Xi, Yinhu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Estimation of rolling friction coefficients in a tribosystem using optical measurements2018In: Industrial Lubrication and Tribology, ISSN 0036-8792, E-ISSN 1758-5775, Vol. 70, no 4, p. 680-686Article in journal (Refereed)
    Abstract [en]

    Purpose

    This paper presents a method to measure the rolling friction coefficient in an easy and fast way. The aim is to measure the rolling friction coefficient between a small steel ball and a cylindrical aluminum surface.

    Design/methodology/approach

    An analytical model of the tribosystem of a freely rolling ball and a cylindrical surface is established. The rolling friction coefficient is evaluated from images recorded by a high-speed camera. The coefficient between a 1.58 mm diameter steel ball and a cylindrical aluminum surface is measured. A background subtraction algorithm is used to determine the position of the small steel ball.

    Findings

    The angular positions of the ball are predicted using the analytical model, and good agreement is found between the experimental and theoretical results.

    Originality/value

    An optical method for evaluating the rolling friction coefficient is presented, and the value of this coefficient between a small steel ball and a cylindrical aluminum surface is evaluated.

  • 36.
    Long, Weishan
    et al.
    School of Air Transportation, Shanghai University of Engineering Science, Shanghai, China.
    Chen, Zhixiong
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. School of Air Transportation, Shanghai University of Engineering Science, Shanghai, China.
    Li, Zhixiong
    School of Engineering, Ocean University of China, Qingdao, China.
    Królczyk, Grzegorz
    Department of Manufacturing Engineering and Automation Products, Opole University of Technology, Opole, 45758, Poland.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A study on the tribological behavior of hybrid and all-steel rough sliding contacts2023In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 237, no 3, p. 562-577Article in journal (Refereed)
    Abstract [en]

    Hybrid bearing is a kind of bearing that uses ceramic materials instead of steel and other metal materials as rolling elements. It is often used to reduce (i.e., rolling or sliding) friction resistance. Although many published works have shown that hybrid bearings are more effective than ordinary bearings in reducing friction resistance, improving service life, and reducing the occurrence of bearing failure, many few works have been focused on the tribological properties of hybrid bearings only under sliding friction conditions. Therefore, it is crucial to understand the tribological behavior of the bearing materials to evaluate the sliding tribological process. In this paper, the tribological properties of silicon nitride-bearing steel friction pair (Si3N4-GCr15 pair) and bearing steel-bearing steel friction pair (GCr15-GCr15 pair) under oil lubrication were experimentally studied. An optical three-dimensional (3D) reconstruction method was used to investigate the microscopic and 3D morphologies of the friction pairs during the wear evolution process. The results show that the changing trends of the micrograph, 3D topography, friction coefficient, and surface roughness are consistent. A wear failure evaluation model was built based on the data extracted from the worn surface morphology. The model indicated that the friction performance of the Si3N4-GCr15 pair is better than that of the GCr15-GCr15 pair. The mechanism of friction performance of different friction pairs under lubrication conditions is studied, which provides good reference for the design of subsequent hybrid bearings.

  • 37.
    Lu, Xinyu
    et al.
    Co-Innovation Center for Efficient Processing and Utilization of Forest Products, College of Chemical Engineering, Nanjing Forestry University, 159 Longpan Road, Nanjing 210037, PR China.
    Gu, Xiaoli
    Co-Innovation Center for Efficient Processing and Utilization of Forest Products, College of Chemical Engineering, Nanjing Forestry University, 159 Longpan Road, Nanjing 210037, PR China.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A review on lignin antioxidants: Their sources, isolations, antioxidant activities and various applications2022In: International Journal of Biological Macromolecules, ISSN 0141-8130, E-ISSN 1879-0003, Vol. 210, p. 716-741Article, review/survey (Refereed)
    Abstract [en]

    Lignin, a biopolymer obtained from agricultural/forestry residues or paper pulping wastewater, is rich in aromatic structure, which is central to its adoption as a candidate to natural antioxidants. Through insight into its structural features from biomass, different functional groups would influence lignin antioxidant activity, wherein phenolic content is the most important factor, hence massive studies have focused on its improvement via different pretreatments and post-processing methods. Besides, lignin nanoparticles and chemical modifications are also efficient methods to improve antioxidant activity via increasing free content and decreasing bond dissociation enthalpy of phenolic hydroxyl. Lignin samples exhibit comparable radicals scavenging ability to commercial ones, showing their potential as renewable alternatives of synthesized antioxidants. Besides, their applications have also been discussed, which demonstrates lignin potential as an inexpensive antioxidant additive and consequent improvements on multiple functionalities. This review is dedicated to summarize lignin antioxidants extracted from biomass resources, methods to improve their antioxidant activity and their applications, which is beneficial for realizing lignin valorization.

  • 38.
    Lu, Xinyu
    et al.
    Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, Jiangsu Provincial Key Lab for the Chemistry and Utilization of Agro-forest biomass, College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, China.
    Gu, Xiaoli
    Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, Jiangsu Provincial Key Lab for the Chemistry and Utilization of Agro-forest biomass, College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, China.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A review on the synthesis of MXenes and their lubrication performance and mechanisms2023In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 179, article id 108170Article, review/survey (Refereed)
    Abstract [en]

    MXenes (MXs), as an emerging 2D family of transition metal carbides and nitrides, have been considered as new candidates for solid lubrication/lubricant additives due to their mono-layered graphene-like structure with similar mechanical properties, abundant surface terminations (i.e., -O, -OH, -F), relatively low shear strength and inherent self-lubrication ability. In this review, we introduced MXs’ synthesis and their lubrication performance and mechanisms. Typically, pure MXs and MXs-based composites like MXs/polymers, MXs/graphene (MoS2) or MXs/metals (metal oxide) were used as reinforcement materials to form protective coatings with excellent mechanical properties and solid lubrication performance. As liquid lubricant additives, MXs can be used as water-/oil-based lubricant additives, and exhibit improved friction and wear. At the same time, chemically functionalized MXs with better dispersibility and compatibility were introduced as the improved oil-based lubricant additives. Some parameters (such as MXs’ structural effects and working conditions) affecting MXs’ lubrication performance, and the lubrication mechanisms (such as the formation of tribofilm, the hydrophilicity-/interlayer-dependent lubrication mechanism and adsorption effect) were all discussed. Finally, some future perspectives for MXs’ lubrication were proposed at the end of this review.

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  • 39.
    Luo, Yanlong
    et al.
    College of Science, Nanjing Forestry University, Nanjing, P. R. China. Institute of Polymer Materials, Nanjing Forestry University, Nanjing 210037, P. R. China.
    Chen, Xianling
    College of Science, Nanjing Forestry University, Nanjing, P. R. China.
    Wu, Sizhu
    State Key Laboratory of Organic−Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, P. R. China.
    Cao, Songyuan
    College of Materials Science and Engineering, Nanjing Tech University, Nanjing 21009, P. R. China.
    Luo, Zhenyang
    College of Science, Nanjing Forestry University, Nanjing 210037, P. R. China. Institute of Polymer Materials, Nanjing Forestry University, Nanjing 210037, P. R. China.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Molecular Dynamics Simulation Study on Two-Component Solubility Parameters of Carbon Nanotubes and Precisely Tailoring the Thermodynamic Compatibility between Carbon Nanotubes and Polymers2020In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 36, no 31, p. 9291-9305Article in journal (Refereed)
    Abstract [en]

    Solubility parameters play an important role in predicting compatibility between components. The current study on solubility parameters of carbon materials (graphene, carbon nanotubes, and fullerene, etc.) is unsatisfactory and stagnant due to experimental limitations, especially the lack of a quantitative relationship between functional groups and solubility parameters. Fundamental understanding of the high-performance nanocomposites obtained by carbon material modification is scarce. Therefore, in the past, the trial and error method was often used for the modification of carbon materials, and no theory has been formed to guide the experiment. In this work, the effect of defects, size, and the number of walls on the Hildebrand solubility parameter (δT) of carbon nanotubes (CNTs) was investigated by molecular dynamics (MD) simulation. Besides, three-component Hansen solubility parameters (δD, δp, δH) were transformed into two-component solubility parameters (δvdW, δelec). The quantitative relation between functional groups and two-component solubility parameters of single-walled carbon nanotubes (SWCNTs) was then given. An important finding is that the δT and δvdW of SWCNTs first decrease, reach a minimum, and then increase with increasing grafting ratio. The thermodynamic compatibility between functionalized SWCNTs and six typical polymers was investigated by the Flory–Huggins mixing model. Two-component solubility parameters were proven to be able to effectively predict their compatibility. Importantly, we theoretically gave the optimum grafting ratio at which the compatibility between functionalized SWCNTs and polymers is the best. The functionalization principle of SWCNTs toward good compatibility between SWCNTs and polymers was also given. This study gives a new insight into the solubility parameters of functionalized SWCNTs and provides theoretical guidance for the preparation of high-performance SWCNTs/polymers composites.

  • 40.
    Ma, Xiaofeng
    et al.
    College of Science, Nanjing Forestry University, Nanjing, P. R. China. Institute of Polymer Materials, Nanjing Forestry University, Nanjing, P. R. China.
    Lan, Xiaoyu
    College of Science, Nanjing Forestry University, Nanjing, P. R. China.
    Wu, Linlin
    College of Materials Science and Engineering, Nanjing Tech University, Nanjing, P. R. China.
    Wang, Lei
    Institute of Polymer Materials, Nanjing Forestry University, Nanjing, P. R. China.
    Gu, Qun
    Chemistry Department, Edinboro University of Pennsylvania, Edinboro PA, USA.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gu, Xiaoli
    College of Chemical Engineering, Nanjing Forestry University, Nanjing, P. R. China.
    Luo, Zhenyang
    College of Science, Nanjing Forestry University, Nanjing, P. R. China. Institute of Polymer Materials, Nanjing Forestry University, Nanjing, P. R. China.
    Photo-induced Actuator using Temperature and Light Dual Responsive Azobenzene Containing Ion Gel in Ionic Liquid2020In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 123, article id 109446Article in journal (Refereed)
    Abstract [en]

    A series of well-defined random copolymers comprising butyl acrylate (BA) and 4-phenylazophenylmethacrylate (AzoMA) (P(AzoMA-r-BA)) are prepared successfully by reversible addition fragmentation chain transfer (RAFT) polymerization. P(AzoMA-r-BA)s show LCST-type phase transition in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfone)amide ([C4mim][NTf2]). LCST depends on the photoisomerization state of azobenzene, as well as on the AzoMA composition in the random copolymers. LCST of (P(cis-AzoMA-r-BA) is significantly higher than that of P(trans-AzoMA-r-BA), because cis-AzoMA and trans-AzoMA behave as solvato-philic and solvato-phobic comonomer, respectively. At a bistable temperature, photo-induced phase separation is completely reversible. Secondly, based on this phenomenon, a thermo- / photo- responsive ion gel (BA-AzoMA ion gel) can be prepared by free radical polymerization of BA and AzoMA using ethylene glycol dimethacrylate (EGDMA) as crosslinker in [C4mim][NTf2]. BA-AzoMA ion gel shows high temperature contraction and low temperature expansion behavior, due to LCST-type phase behavior of polymer system consisting of AzoMA and BA. Contraction temperature of BA-AzoMA ion gel depends on photoisomerization state of the azobenzene group in polymers. At a bistable temperature, photo-induced expansion-contraction is reversible. Finally, a Photo-induced actuator can be realized using BA-AzoMA ion gel at suitable temperatures, featuring reversible bending by alternate irradiating with visible and UV light. The bending behavior is also demonstrated.

  • 41.
    Man, Weizhen
    et al.
    School of Advanced Materials and Mechatronic Engineering, Hubei Minzu University, Enshi, 445000, China.
    Huang, Yiyao
    College of Mechanical and Electrical Engineering, Beijing University of Chemical Technology, Beijing, 100029, China.
    Gou, Hetong
    College of Mechanical and Electrical Engineering, Beijing University of Chemical Technology, Beijing, 100029, China.
    Li, Yingru
    School of Advanced Materials and Mechatronic Engineering, Hubei Minzu University, Enshi, 445000, China.
    Zhao, Jun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. College of Mechanical and Electrical Engineering, Beijing University of Chemical Technology, Beijing, 100029, China.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Synthesis of novel CuO@Graphene nanocomposites for lubrication application via a convenient and economical method2022In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 498-499, article id 204323Article in journal (Refereed)
    Abstract [en]

    Graphene-based nano lubricant additives attract more and more attention because of their superior lubricating performance as well as green and ashless properties. Graphene-based nanocomposites exhibit excellent tribological performances due to the synergistic “slide-roll” effect. In this work, we developed a novel nanocomposite constructed by graphene materials (G) and CuO nanoparticles, named CuO@G, which has superior tribological properties to each component (pure CuO or pure graphene materials) and the mixture (Graphene + CuO) under different testing conditions due to the synergistic effect. By adding 0.5 wt% CuO@G to PAO-6 oil, the coefficient of friction (COF) is reduced by more than 50%, and the wear scar almost disappears. The study provides a novel and promising method for the synthesis of graphene-based lubrication nanomaterials, which has high potential for lubrication applications.

  • 42.
    Mehamud, Idiris
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Self-powered online practical machine condition monitoring and wireless communication achieved on integrated, efficient, and durable triboelectric nanogenerator2024In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 123, article id 109439Article in journal (Refereed)
    Abstract [en]

    Triboelectric nanogenerator (TENG) can effectively scavenge ambient mechanical energy with cost, weight, and effectiveness advantages despite critical issues of TENG such as integration to complex components, low current output, and durability. In this work, we designed an adaptive TENG on a mechanical shaft for harvesting rotational energy which can easily assemble and disassemble. The proposed TENG presents an excellent performance for a wide range of rotational speeds (0–2000rpm) and delivers a high power of up to about 80mW (a high short circuit current of 3mA) for a size of 216 cm3, which is high enough for many types of machine condition monitoring purposes. The designed TENG has been evaluated under the noncontact mode of operation within a 0–0.5mm gap between TENG films. The TENG demonstrates excellent electrical stability of 99% without surface wear under noncontact mode within the whole test period for continuous operation of 420,000 cycles. The contact mode with a contact pressure of 0.76 Pa results in 90% electrical stability and apparent surface degradation. Moreover, it is demonstrated that the proposed TENG can power a wireless vibration sensor (60 mW) within 10 minutes energy harvesting for 9 seconds to send data via Bluetooth to a smartphone at up to 30 m, and a wireless temperature sensor (1.2 mW) in real-time for machine condition monitoring.

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  • 43.
    Mehamud, Idiris
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Small Size and Low-Cost TENG-Based Self-Powered Vibration Measuring and Alerting System2023In: Advanced Electronic Materials, E-ISSN 2199-160X, Vol. 9, no 6, article id 2300111Article in journal (Refereed)
    Abstract [en]

    Vibration measurement systems containing sensors, signal conditioning, and data acquisition devices, are important for monitoring motors, gearboxes, turbines, etc. Microelectromechanical and piezoelectric sensors are predominantly used for vibration measurements. However, they are not cost-effective, flexible in design, and incapable of self-powering. Recently, triboelectric nano-generator (TENG)-based vibration sensors have been considered as a possible alternative to resolve this problem, and tremendous progress has been achieved. Previous work on TENG-based sensors is limited to optimizing the sensor design, while the signal conditioning and data acquisition of TENG signal still need investigation for actual applications. This work develops a TENG-based vibration measurement device and self-powered alerting system that is integrated with the signal condition and data acquisition systems. The experimental results show that the proposed measurement system successfully measures signals within the range of 0–1800 Hz frequency. Meanwhile, the TENG generates a high output, up to 80 V and 0.55 µA from small size TENG area (3.6 cm2). The signal is adequate to harvest energy for self-powering to drive alerting components (harvest 320 mJ in 36 h, which drives alarming for duration of 1.5 s). The proposed device is cost-effective (30 $), small (105 cm3), and consumes less power (0.18 W) in comparison to commercial devices.

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  • 44.
    Mehamud, Idiris
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Machine condition monitoring enabled by broad range vibration frequency detecting triboelectric nano-generator (TENG)-based vibration sensors2022In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 98, article id 107292Article in journal (Refereed)
    Abstract [en]

    Vibration analysis is an efficient method to monitor machine condition status. Different types of vibration sensors, such as microelectromechanical, and piezoelectric accelerometers have been used to measure vibrations, but face the problems of relying on external power and high cost. Recently, triboelectric nano-generator (TENG)-based vibration sensors have attracted attention to solve these problems. However, previous studies on TENG-based mechanical vibration sensors are limited to a low-frequency range (less than 200 Hz), which is below industry machine condition monitoring requirements (often 10-1000 Hz). This work aims at enabling TENG-based vibration sensors for higher frequencies and a broad range of frequency detection through structural design supported by numerical simulations. Numerical simulation results indicate that the frequency detection range is controlled by structural design and can be easily expanded for high-frequency detection by reducing the size and improving the shape of the structure. Spring-assisted TENG-based vibration sensors with the possibility of detecting the vibration within 0-1200 Hz, which covers the major mechanical failures and imperfections in vibrational frequency ranges, are prepared according to the structural design and numerical simulation results. The experimental results show that the developed sensor successfully detects signals within the frequency range of 0-1200 Hz. Due to optimized structural symmetry and effective spring stiffness, the two spring-assisted (TS) structures generate higher electric signal output (up to 200 V and 0.9 µA). The prepared TENG vibration sensors are further compared with a high-quality commercial vibration sensor in terms of vibrational signal response and detecting bearing defects. The results show that the prepared TENG vibration sensors can provide at least the same function as the commercial vibration sensor and demonstrate a promising potential to detect machine working conditions.

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  • 45.
    Mu, Liwen
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. State Key Laboratory of Materials‐Oriented Chemical Engineering, Nanjing Tech University, Nanjing, 210009 P. R. China.
    Cao, Danyang
    State Key Laboratory of Materials‐Oriented Chemical Engineering, Nanjing Tech University, Nanjing, 210009 P. R. China.
    Zhuang, Wei
    State Key Laboratory of Materials‐Oriented Chemical Engineering, Nanjing Tech University, Nanjing, 210009 P. R. China. College of Biotechnology and Pharmaceutical Engineering, National Engineering Technique Research Center for Biotechnology, Nanjing Tech University, No. 30, Puzhu South Road, Nanjing, 211816 China.
    Yu, Qiangliang
    State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Lanzhou, 730000 China.
    Cai, Meirong
    State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Lanzhou, 730000 China.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Stable Dispersed Zeolitic Imidazolate Framework/Graphene Oxide Nanocomposites in Ionic Liquids Resulting in High Lubricating Performance2020In: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 7, no 9, article id 1902194Article in journal (Refereed)
    Abstract [en]

    The “block‐on‐plate” nanocomposite structure material is realized with the zeolitic imidazolate framework (ZIF‐67) on graphene oxide (GO) with surface oxygen‐rich functional groups. Scanning electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffractograms, fourier transform infrared spectroscopy, and ZIF‐67/GO demonstrate a high capability of promoting the lubricating performance of [Choline][Proline] ([CH][P]) bio‐ionic liquid. Specifically, the wear volume of the disc by [CH][P]‐0.1 ZIF‐67/GO is only 52% of the one lubricated by pure [CH][P]. Moreover, ZIF‐67/GO shows a long time, high dispersion stability in [CH][P]. In addition, the combination of GO nanosheets and ZIF‐67 can make ZIF‐67/GO have better polishing effect between the steels during the friction process, which can effectively form a robust lubrication layer and improves overall lubricating properties. As a result, the interfacial lubrication can be significantly improved by these newly developed [CH][P]‐ZIF‐67/GO lubricants. This work offers a new promising application for ZIF‐67 nanocomposites with GO in advanced lubrication systems. This work also provides a new strategy of producing lubricants containing nanoparticles with high dispersion stability, which may solve the biggest challenge in this field.

  • 46.
    Mu, Liwen
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Dong, Yuguo
    College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, China.
    Li, Licheng
    College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, China.
    Gu, Xiaoli
    College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, China.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Achieving High Value Utilization of Bio-oil from Lignin Targeting for Advanced Lubrication2021In: ES Materials & Manufacturing, ISSN 2578-0611, Vol. 11, p. 72-80Article in journal (Refereed)
    Abstract [en]

    High-value utilization of biomass has been driven by increasingly growing industrial demands. Herein, we offer a strategy composed of depolymerization and esterification reaction of lignin to transfer to bio-oil with high liquid yield (79.75~85.25%), which is demonstrated as a high performance lubricant. Overall, the bio-oil has the excellent lubrication properties, where a significant wear reduction of 97.6% was observed as compared with polyethylene glycol 200. Meanwhile, the more ether and less acid in bio-oil could improve the anti-wear properties. This work provides a new application of utilizing lignin in advanced lubrication systems.

  • 47.
    Mu, Liwen
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    He, Jian
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Li, Yifan
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Ji, Tuo
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Mehra, Nitin
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Zhu, Jiahua
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Molecular Origin of Efficient Phonon Transfer in Modulated Polymer Blends: Effect of Hydrogen Bonding on Polymer Coil Size and Assembled Microstructure2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 26, p. 14204-14212Article in journal (Refereed)
    Abstract [en]

    Molecular level engineering of polymer or polymer blends has been recently demonstrated effective strategy to regulate thermal conductivity. Such materials are of great interest to meet critical requirements of transparent, light weight, flexible, etc for thermal management in electronic applications. In this work, modulated polymer blends with poly(vinyl alcohol) (PVA) and biopolymers (lignin, gelatin) were designed and significantly enhanced thermal conductivity was achieved by tuning the intermolecular interaction among polymer components. The hydrogen bond interaction has been revealed as the major driving force that affects the polymer coil dimension in aqueous solution, the microstructure of coil-coil interaction in solid film and thus the thermal conduction. A solid relationship across molecular level interaction to macro-scale thermal conduction is constructed via careful characterization of the coil size in liquid phase and assembled microstructure in solid phase. Appropriate integration of biopolymers and PVA is essential to achieve synergistic effect. Specifically, thermal conductivity of polymer blend with 10% lignin and 10% G90 in PVA reaches 0.71 W/m·K, which is 184% enhancement as compared to pure PVA. This work reveals the fundamental molecular origin of polymer blends in association with thermal conductivity and has great potential to guide molecular engineering for superior physicochemical properties.

  • 48.
    Mu, Liwen
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ji, Tuo
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Chen, Long
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Mehra, Nitin
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Zhu, Jiahua
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Paving the Thermal Highway with Self-Organized Nanocrystals in Transparent Polymer Composites2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 42, p. 29080-29087Article in journal (Refereed)
    Abstract [en]

    Phonon transfer is greatly scattered in traditional polymer composites due to the unpaired phonon frequency at the polymer/filler interface. A key innovation of this work is to build continuous crystal network by self-organization and utilize it as “thermal highway” that circumvents the long-existing interfacial thermal barrier issue in traditional composites. By tuning the molecular diffusion rate of dicarboxylic acids (oxalic acid, malonic acid, and succinic acid), different crystal structures including skeletal, dendrite, diffusion-limited aggregates, and spherulite were synthesized in PVA film. These continuous crystal structures benefit the efficient phonon transfer in the composites with minimized interfacial scattering and lead to a significant thermal conductivity enhancement of up to 180% compared to that of pure polymer. Moreover, the transparent feature of these composite films provides additional benefits in display applications. The post heat treatment effect on the thermal conductivity of the composite films shows a time-dependent behavior. These uniquely structured polymer/crystal composites are expected to generate significant impacts in thermal management applications.

  • 49.
    Mu, Liwen
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. The University of Akron, Akron, USA.
    Ma, Xiaofeng
    Nanjing Forestry University, Nanjing, PR China.
    Guo, Xiaojing
    Chinese Academy of Sciences, Shanghai, PR China.
    Chen, Minjiao
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ji, Tuo
    The University of Akron, Akron, USA.
    Hua, Jing
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Zhu, Jiahua
    The University of Akron, Akron, USA.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Structural strategies to design bio-ionic liquid: Tuning molecular interaction with lignin for enhanced lubrication2019In: Journal of Molecular Liquids, ISSN 0167-7322, E-ISSN 1873-3166, Vol. 280, p. 49-57Article in journal (Refereed)
    Abstract [en]

    Lignin strengthened ionic liquids (ILs) have shown high potential to be used as high performance green lubricants. Strengthened lignin-ILs molecular interaction is an effective approach to improve their lubrication properties. The molecular interactions of ILs’ cation and anion containing different functional groups with lignin and efficiency on the lubricating properties have rarely been studied yet. In this work, a series of novel green lubricants with dissolved lignin in [Choline][Amino Acid] ([CH][AA]), [Tetramethylammonium][Glycine] ([N 1111 ][Gly]) and [Tetrabutylammonium][Glycine] ([N 4444 ][Gly]) ILs have been synthesized and their tribological properties were systematically investigated. The longer alkyl chain in cation without reciprocal H-bond interaction between ILs’ cation and anion has the positive effect on the anti-wear properties. In addition, the less steric effect and more negative natural charges of amino acid anion synergistically contribute to the stronger H-bond interaction between lignin and choline base ILs, which enhances lubrication film strength and thus resulting in the better tribological property of ILs/lignin green lubricants. Specifically, the wear volume loss of the steel disc lubricated by [N 4444 ][Gly] with the addition of 15% lignin is only 12% of the one lubricated by pure [N 4444 ][Gly]. This work presents a method to tune molecular interaction between lignin and ILs via the structural design of ILs’ cation and anion, which are revealed as the key factor that bridges the individual components and improves overall lubricating properties. 

  • 50.
    Mu, Liwen
    et al.
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Chen, Long
    Department of Chemical and Biomolecular Engineering, The University of Akron, Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Ji, Tuo
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Yuan, Ruixia
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Wang, Huaiyuan
    School of Chemistry & Chemical Engineering, Northeast Petroleum University, College of Chemistry and Chemical Engineering, Northeast Petroleum University, Daqing.
    Zhu, Jiahua
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    [N-Methyl-2-pyrrolidone][C1–C4 carboxylic acid]: novel solvent system with exceptional lignin solubility2015In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 51, no 70, p. 13554-13557Article in journal (Refereed)
    Abstract [en]

    Novel solvent systems composed of N-methyl-2-pyrrolidone and C1–C4 carboxylic acid exhibit unique physicochemical properties, e.g. large polarity, low viscosity and excellent hydrogen bonding capacity, which have demonstrated excellent lignin solubility that outperforms conventional solvents and ionic liquids.

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