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Shao, J., Willatzen, M., Shi, Y. & Wang, Z. L. (2019). 3D mathematical model of contact-separation and single-electrode mode triboelectric nanogenerators. Nano Energy, 60, 630-640
Open this publication in new window or tab >>3D mathematical model of contact-separation and single-electrode mode triboelectric nanogenerators
2019 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 60, p. 630-640Article in journal (Refereed) Published
Abstract [en]

Based on a set of finite-sized charged planes (FSCP), a simple time-dependent three-dimensional spatial model for the electric potential and electric field in an inhomogeneous medium composed of dielectric materials and metal contacts is proposed and used to assert triboelectric nanogenerator operation. Solving the problem of FSCP makes the three-dimensional spatial model relevant for practical TENG applications and allow for accurate and reliable results. Connecting the metal contacts to an electric resistance, Kirchhoff's law is used to derive a first-order time-dependent differential equation for the mobile charges on the metal contacts and the displacement current. Specially, the displacement current (Maxwell's displacement current) in a TENG equals to the conduction current in the external circuit is obtained. We then consider two important types of triboelectric nanogenerators: the contact-separation (CS) mode and the single-electrode (SEC) mode. A forced movement of the dielectric materials and/or the metal contacts leads to currents flowing in the system and a time-varying electrical potential, and therefore the generation of electrical power. Then, new and more accurate capacitance equations for CS and SEC modes of TENGs are extracted. Several examples of energy harvesting scenarios are finally analyzed.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
triboelectric nanogenerator, 3D mathematical model, Displacement current, Contact-mode, Single-electrode mode
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-73336 (URN)10.1016/j.nanoen.2019.03.072 (DOI)000467774100069 ()2-s2.0-85063899114 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-04-12 (johcin)

Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-06-18Bibliographically approved
Chen, J., Li, F., Luo, Y., Shi, Y., Ma, X., Zhang, M., . . . Luo, Z. (2019). A self-healing elastomer based on an intrinsic non-covalent cross-linking mechanism. Journal of Materials Chemistry A, 7(25), 15207-15214
Open this publication in new window or tab >>A self-healing elastomer based on an intrinsic non-covalent cross-linking mechanism
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2019 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, no 25, p. 15207-15214Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2019
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-74367 (URN)10.1039/C9TA03775F (DOI)000473054500023 ()2-s2.0-85068172124 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-07-12 (johcin)

Available from: 2019-06-11 Created: 2019-06-11 Last updated: 2019-07-12Bibliographically approved
Hua, J., Björling, M., Grahn, M., Larsson, R. & Shi, Y. (2019). A smart friction control strategy enabled by CO2 absorption and desorption. Scientific Reports, 9(1), Article ID 13262.
Open this publication in new window or tab >>A smart friction control strategy enabled by CO2 absorption and desorption
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2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, no 1, article id 13262Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2019
National Category
Chemical Process Engineering Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Chemical Technology; Machine Elements
Identifiers
urn:nbn:se:ltu:diva-76046 (URN)10.1038/s41598-019-49864-w (DOI)000485680900059 ()31519987 (PubMedID)2-s2.0-85072208170 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-09-18 (johcin)

Available from: 2019-09-18 Created: 2019-09-18 Last updated: 2019-10-25Bibliographically approved
Björling, M. & Shi, Y. (2019). DLC and Glycerol: Superlubricity in Rolling/Sliding Elastohydrodynamic Lubrication. Tribology letters, 67(1), Article ID 23.
Open this publication in new window or tab >>DLC and Glycerol: Superlubricity in Rolling/Sliding Elastohydrodynamic Lubrication
2019 (English)In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 67, no 1, article id 23Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Traction, EHL, Coatings, friction reducing, Superlubricity, Friction, Thermal effects in EHL, DLC, Glycerol
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-72541 (URN)10.1007/s11249-019-1135-1 (DOI)000455190400002 ()2-s2.0-85059784212 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-01-25 (inah)

Available from: 2019-01-14 Created: 2019-01-14 Last updated: 2019-01-25Bibliographically approved
Zhang, Y., Zhu, W., Li, J., Zhu, Y., Wang, A., Lu, X., . . . Shi, Y. (2019). Effects of ionic hydration and hydrogen bonding on flow resistance of ionic aqueous solutions confined in molybdenum disulfide nanoslits: Insights from molecular dynamics simulations. Fluid Phase Equilibria, 489, 23-29
Open this publication in new window or tab >>Effects of ionic hydration and hydrogen bonding on flow resistance of ionic aqueous solutions confined in molybdenum disulfide nanoslits: Insights from molecular dynamics simulations
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2019 (English)In: Fluid Phase Equilibria, ISSN 0378-3812, E-ISSN 1879-0224, Vol. 489, p. 23-29Article in journal (Refereed) Published
Abstract [en]

Single-layer molybdenum disulfide (MoS2) is a novel two-dimensional material that has attracted considerable attention because of its excellent properties. In this work, molecular dynamics simulations were performed to investigate the effect of different kinds of alkali metal ions (Li+, Na+, and K+) on the flow resistance of ionic aqueous solutions confined in MoS2 nanoslits under shearing. Three slit widths (i.e. 1.2, 1.6, and 2.0 nm) were investigated. Simulation results showed that the friction coefficient followed the order of K+ < Na+ < Li+. The friction coefficient decreased with the increasing of slit width. Unique confined spatial distributions of different types of ionic aqueous solutions led to different confined ionic hydrations for different cations. These differences lead to different orientations of surrounding water molecules and then form different hydrogen bond (HB) networks. The friction coefficient was greatly dependent on the number of HBs per water; i.e., the larger the number of HBs formed, the lower was the flow resistance.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
MoS2, Ionic aqueous solutions, Molecular simulations, Flow resistance, Nanoconfinement
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-72909 (URN)10.1016/j.fluid.2019.02.012 (DOI)000465056300004 ()2-s2.0-85061545923 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-02-26 (svasva)

Available from: 2019-02-15 Created: 2019-02-15 Last updated: 2019-05-02Bibliographically approved
Zhu, W., Zhang, C., Zhu, Y.-d., An, R., Lu, X.-h., Shi, Y.-j. & Jiang, S.-y. (2019). Molecular insights on the microstructures of nanoconfined glycerol and its aqueous solutions: The effects of interfacial properties, temperature, and glycerol concentration. Journal of Molecular Liquids, 291, Article ID 111238.
Open this publication in new window or tab >>Molecular insights on the microstructures of nanoconfined glycerol and its aqueous solutions: The effects of interfacial properties, temperature, and glycerol concentration
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2019 (English)In: Journal of Molecular Liquids, ISSN 0167-7322, E-ISSN 1873-3166, Vol. 291, article id 111238Article in journal (Refereed) Published
Abstract [en]

In this work, we conducted molecular dynamics simulations to investigate the effects of rutile–liquid and graphene–liquid interfacial properties, glycerol concentrations (i.e., 10%, 40%, 70%, and 100% molar contents), and temperature (i.e., 180, 273, and 320 K) on the microstructures of nanoconfined glycerol and its aqueous solutions. Results indicated that the effect of interfacial properties on the spatial and orientation distributions of nanoconfined glycerol and water molecules was more prominent than that of temperature. In glycerol aqueous solutions, water and glycerol molecules localized into two distinct layers on the hydrophilic rutile surface but partially mixed with each other near the hydrophobic graphene surface, because water molecules near the hydrophobic surface exhibited more random orientations and formed more hydrogen bonds with glycerol molecules than those near the hydrophilic surface. Moreover, interface introduction and increased temperature drastically reduced the hydrogen bonding ability of water molecules in glycerol aqueous solutions. The addition of glycerol molecules can break hydrogen bonds between water molecules and inhibit water crystallization in glycerol aqueous solutions. Temperature and glycerol concentration exerted limited effects on the hydrogen bonding ability of water molecules on hydrophilic surfaces in glycerol aqueous solutions. Meanwhile, the presence of a hydrophilic surface can effectively decelerate hydrogen bond breakage induced by increasing temperature or by decreasing glycerol contents

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Glycerol, Microstructure, Molecular dynamics simulations
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-75260 (URN)10.1016/j.molliq.2019.111238 (DOI)000487168000026 ()2-s2.0-85068578823 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-08-22 (johcin)

Available from: 2019-07-09 Created: 2019-07-09 Last updated: 2019-10-10Bibliographically approved
Hua, J. & Shi, Y. (2019). Non-corrosive Green Lubricant With Dissolved Lignin in Ionic Liquids Behave as Ideal Lubricants for Steel-DLC Applications. Frontiers in Chemistry, 7, Article ID 857.
Open this publication in new window or tab >>Non-corrosive Green Lubricant With Dissolved Lignin in Ionic Liquids Behave as Ideal Lubricants for Steel-DLC Applications
2019 (English)In: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 7, article id 857Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2019
Keywords
lubricants, ionic liquids, ILs, lignin, DLC
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-77086 (URN)10.3389/fchem.2019.00857 (DOI)
Note

Validerad;2019;Nivå 2;2019-12-11 (johcin)

Available from: 2019-12-06 Created: 2019-12-06 Last updated: 2019-12-11Bibliographically approved
Yu, Q., Zhang, C., Dong, R., Shi, Y., Wang, Y., Bai, Y., . . . Zhou, F. (2019). Novel N, P-containing oil-soluble ionic liquids with excellent tribological and anti-corrosion performance. Tribology International, 132, 118-129
Open this publication in new window or tab >>Novel N, P-containing oil-soluble ionic liquids with excellent tribological and anti-corrosion performance
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2019 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 132, p. 118-129Article in journal (Refereed) Published
Abstract [en]

Two oil-soluble ionic liquids N, N-trimethyl-N-hexadecyl ammonium bis(2-ethylhexyl) phosphate (NP-16))and 1,2-bis-NN-dimethyl-N-cetylammonium bis (2-ethylhexyl) phosphate (NP-16-2-16) have been synthesized and investigated as a potential friction reduction and anti-wear lubricant additive with anti-corrosion properties. The results indicate that the addition of 1.0 wt % NP-16 into PAO10 can significantly reduce friction coefficient and improve its anti-wear performance under RT and 100 °C. The performance is obviously better than that of traditional additives ZDDP and tricresyl phosphate. PAO10 + 1.0 wt % NP-16 even outperformed the PAO10 with about 40% lower friction and 2 orders of magnitude less wear. The analysis results of SEM, EDS and XPS show that an FePO4 or nitrogen-containing tribofilm is formed on the friction interface when NP-16 and NP-16-2-16 are selected as additives, which play a key role in reducing friction and wear.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Oil-soluble ionic liquids, Lubricity, Anti-wear performance, Lubricating mechanism
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-72457 (URN)10.1016/j.triboint.2018.12.002 (DOI)000456758700012 ()2-s2.0-85058810711 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-01-04 (svasva)

Available from: 2019-01-04 Created: 2019-01-04 Last updated: 2019-02-11Bibliographically approved
Wu, J., Mu, L., Feng, X., Lu, X., Larsson, R. & Shi, Y. (2019). Poly(alkylimidazolium bis(trifluoromethylsulfonyl) imide)-Based Polymerized Ionic Liquids: A Potential  High-Performance Lubricating Grease. Advanced Materials Interfaces, 6(5), Article ID 1801796.
Open this publication in new window or tab >>Poly(alkylimidazolium bis(trifluoromethylsulfonyl) imide)-Based Polymerized Ionic Liquids: A Potential  High-Performance Lubricating Grease
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2019 (English)In: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 6, no 5, article id 1801796Article in journal (Refereed) Published
Abstract [en]

Polymers prepared from ionic liquids are widely called polymerized ionic liquids (PILs). Compared to monocationic and dicationic ILs, PILs have higher molecular weights, charge, and greater intermolecular interactions, which make PILs have a higher possibility to generate better lubricity. PILs of poly‐alkylimidazolium bis(trifluoromethylsulfonyl)imide (PImC6NTf2) is studied herein. Dicationic ILs of 1,1′‐(pentane‐1,5‐diyl)‐bis(3‐butylimidazolium) bis(trifluoromethylsulfonyl)imide (BIm5‐(NTf2)2) is used as additive to decrease the crystallization temperature of PImC6NTf2. Lubricity of PImC6NTf2 and PImC6NTf2+BIm5‐(NTf2)2, as well as BIm5‐(NTf2)2 for comparison is evaluated under severe conditions, i.e., 3.0 to 3.5 GPa and 200 °C. The rheological study suggests that PImC6NTf2 can be classified into grease. Tribological test results show that PImC6NTf2 has much better antiwear property than BIm5‐(NTf2)2, especially at 3.5 GPa. Adding 4% BIm5‐(NTf2)2 to PImC6NTf2 is able to reduce friction under high pressure. At 200 °C, PImC6NTf2 exhibits excellent lubricity. The mixture of 96%PImC6NTf2+4%BIm5‐(NTf2)2 shows even better antiwear property than neat PImC6NTf2 and exhibits the highest friction reducing property among the ILs at 200 °C. It is speculated that the robust strength of PILs and strong adhesion between PILs and solids are key factors in achieving the excellent antiwear property.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
grease, high pressure and high temperature, lubricity, polymerized ionic liquids
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-72623 (URN)10.1002/admi.201801796 (DOI)000460657100002 ()
Note

Validerad;2019;Nivå 2;2019-03-11 (johcin)

Available from: 2019-01-18 Created: 2019-01-18 Last updated: 2019-06-14Bibliographically approved
Shetty, P., Mu, L. & Shi, Y. (2019). Polyelectrolyte Cellulose Gel with PEG/Water: Toward Fully Green Lubricating Grease. Carbohydrate Polymers
Open this publication in new window or tab >>Polyelectrolyte Cellulose Gel with PEG/Water: Toward Fully Green Lubricating Grease
2019 (English)In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344Article in journal (Refereed) Epub ahead of print
Abstract [en]

Developing a fully green lubricant is an urgent need due to the growing consciousness of environmental protection and dwindling resources. In this work, fully green gel lubricants were developed out of cellulose derivatives as gelator and mixture of water and poly(ethylene glycol) 200 (PEG 200) as the base fluid. The non-ionic hydroxyethyl cellulose (HEC) and anionic sodium carboxymethyl cellulose (NaCMC) were chosen to understand the effect of ionic and non-ionic gelators on the thermal, rheological and the tribological properties of the gel lubricant. HEC or NaCMC is demonstrated as effective additive to reduce wear, stabilize friction coefficient and enhance the thermal stability of developed lubricants. It is shown that anionic gelator will result in producing lower friction and wear in comparison to non-ionic gelator, which may be attributed to the possible tribo-film formation due to the negative charge in the NaCMC molecules and its larger molecular weight.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Cellulose, Green, lubricant, PEG/Water, Gel
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-76921 (URN)10.1016/j.carbpol.2019.115670 (DOI)
Available from: 2019-11-28 Created: 2019-11-28 Last updated: 2019-11-28
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ORCID iD: ORCID iD iconorcid.org/0000-0001-6085-7880

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