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Open Access Research Article Issue
A robust membrane with dual superlyophobicity for solving water-caused lubricant deterioration and water contamination
Friction 2023, 11 (8): 1442-1454
Published: 17 January 2023
Downloads:11

Lubricants are often contaminated by water in different ways. Water-polluted lubricants extremely accelerate wear corrosion, leading to the deterioration of lubricity performance. Recently, multiphase media superwettability has been developed to endow one surface with compatible functions, such as on-demand separation of oily wastewater. However, realizing the robustness of the dual superlyophobic surface to solve water-caused lubricant deterioration and water contamination as needed remains challenges. Herein, a robust dual superlyophobic membrane is presented to realize on-demand separation for various lubricant–water emulsions. Compared to pure lubricants, the purified lubricants have equivalent tribology performance, which are much better than that of water-polluted lubricants. The as-prepared membrane maintains dual superlyophobicity, high-efficient for water or lubricant purification, and excellent tribology performance of the purified lubricant, even after immersion in hot liquids for 24 h, multicycle separation, and sandpaper abrasion for 50 cycles. Water-polluted lubricant extremely accelerates wear corrosion to promote catalytic dehydrogenation of lubricants, generating too much harmful carbon-based debris. This work shows great guiding significance for recovering the tribology performance of water-polluted lubricants and purifying water by the dual superlyophobic membrane.

Open Access Review Article Issue
Low friction of superslippery and superlubricity: A review
Friction 2023, 11 (7): 1121-1137
Published: 10 August 2022
Downloads:105

The issues regarding energy dissipation and component damage caused by the interface friction between a friction pair attract enormous attention to friction reduction. The key-enabling technique to realize friction reduction is the use of lubricants. The lubricants smooth the contact interfaces, achieving an ultralow friction contact, which is called superslippery or superlubricity. At present, superslippery and superlubricity are two isolated research topics. There is a lack of unified definition on superslippery and superlubricity from the viewpoint of tribology. Herein, this review aims at exploring the differences and relations between superslippery and superlubricity from their origin and application scenarios. Meanwhile, the challenges for developing superslippery surface and superlubricity surface are discussed. In addition, perspectives on the interactive development of these two surfaces are presented. We hope that our discussion can provide guidance for designing superslippery or superlubricity surfaces by using varies drag-reduction technologies.

Open Access Research Article Issue
Electron transfer dominated triboelectrification at the hydrophobic/slippery substrate–water interfaces
Friction 2023, 11 (6): 1040-1056
Published: 08 July 2022
Downloads:21

Triboelectric nanogenerator (TENG) based on triboelectrification has attracted wide attention due to its effective utilization of green energy sources such as marine energy. However, researches about liquid–liquid triboelectrification are still scanty as solid–liquid triboelectrification has been widely studied. Herein, this work focuses on the hydrophobic/slippery substrate–water interfacial triboelectrification based on the solid friction materials of polytetrafluoroethylene (PTFE) nanoparticles. The hydrophobic/slippery substrate–water interfacial triboelectrification are studied by assembling PTFE coated Al sheets and perfluoropolyether (PFPE) infused PTFE coated Al sheets (formed the slippery lubricant-infused surfaces (SLIPSs)) as the friction electrode, and water as liquid friction materials, respectively. The results show that the hydrophobic TENG output performances improved as the PTFE nanoparticles cumulating, and the SLIPSs TENG output performances increased with the thinner PFPE thickness. Both the triboelectrification behavior of hydrophobic/SLIPSs TENG assembled in this work are dominated by the electron transfer. Thanks to the introduction of SLIPSs, the SLIPSs TENG exhibits superior stability and durability than the hydrophobic TENG. The investigation of hydrophobic/slippery substrate–water interfacial triboelectrification contributes to optimize the TENG performances, and expands the application in harsh environments including low temperature and high humidity on the ocean.

Open Access Research Article Issue
Lubricant self-replenishing slippery surface with prolonged service life for fog harvesting
Friction 2022, 10 (10): 1676-1692
Published: 04 September 2021
Downloads:13

Slippery lubricant-infused surfaces exhibit excellent fog-harvesting capacities compared with superhydrophobic and superhydrophilic surfaces. However, lubricant depletion is typically unavoidable under dynamic conditions, and reinfused oil is generally needed to recover the fog-harvesting capacity. Herein, an effective strategy for delaying the depletion of lubricant to prolong the service life of fog harvesting is proposed. An ultrathin transparent lubricant self-replenishing slippery surface was fabricated via facile one-step solvent evaporation polymerization. The gel film of the lubricant self-replenishing slippery surface, which was embedded with oil microdroplets, was attached to glass slides via the phase separation and evaporation of tetrahydrofuran. The gel film GFs-150 (with oil content 150 wt% of aminopropyl-terminated polydimethyl siloxane (PDMS–NH2)) exhibited superior slippery and fog-harvesting performance to other gel films. Furthermore, the slippery surfaces with the trait of oil secretion triggered by mechanical stress exhibited better fog-harvesting capabilities and longer service life than surfaces without the function of lubricant self-replenishment. The lubricant self-replenishing, ultrathin, and transparent slippery surfaces reported herein have considerable potential for applications involving narrow spaces, visualization, long service life, etc.

Open Access Research Article Issue
Computational investigation of the lubrication behaviors of dioxides and disulfides of molybdenum and tungsten in vacuum
Friction 2017, 5 (1): 23-31
Published: 07 March 2017
Downloads:16

Lamellar compounds such as the disulfides of molybdenum and tungsten are widely used as additives in lubricant oils or as solid lubricants in aerospace industries. The dioxides of these two transition metals have identical microstructures with those of the disulfides. The differences in the lubrication behaviors of disulfide and dioxides were investigated theoretically. Tungsten dioxide and molybdenum dioxide exhibit higher bond strengths at the interface and lower interlayer interactions than those of the disulfides which indicates their superlubricity. Furthermore, the topography of the electron density of the single layer nanostructure determined their sliding potential barrier; the dioxides showed a weaker electronic cloud distribution between the two neighboring oxygen atoms, which facilitated the oxygen atoms of the counterpart to go through. For commensurate friction, the dioxides exhibited nearly the same value of friction work, and same was the case for the disulfides. The lower positive value of friction work for the dioxides confirmed their improved lubricity than the disulfides and the higher mechanical strength of the bulk dioxides demonstrated that they are excellent solid lubricants in vacuum.

Open Access Research Article Issue
Characterizing a lubricant additive for 1,3,4-tri-(2-octyldodecyl) cyclopentane: Computational study and experimental verification
Friction 2016, 4 (3): 257-265
Published: 09 September 2016
Downloads:17

In order to increase the life of spacecraft, it is important to improve the comprehensive lubrication performance. Multiple alkylated cyclopentane (MAC) lubricants are presently gaining wide acceptance for actual space applications; adding extreme pressure additive is a strategy to improve lubrication performance. In this study, taking 1,3,4-tri-(2-octyldodecyl) cyclopentane as base oil, tricresol phosphate (traditional additive) and tri-(2-octyldodecyl) phosphate (developmental additive) have been screened computationally for compatibility, shear film forming and energy dissipation. Theoretical results indicate that (a) tricresol phosphate additive is not suited for addition to 1,3,4-tri-(2-octyldodecyl) cyclopentane lubricant due to limited compatibility; (b) tri-(2-octyldodecyl) phosphate is an excellent lubricant additive due to its perfect compatibility, ease of forming a shear film on the surface of friction pairs, higher strength, and low energy dissipation; and (c) lubrication occurs through the solid-liquid composite lubrication mechanism. These theoretical results were confirmed experimentally.

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