Meirong Cai

Imidazolium Ionic Liquids As Antiwear and Antioxidant Additive in Poly(ethylene glycol) for Steel/Steel Contacts

Three imidazolium-based ionic liquids containing sterically hindered phenol groups were synthesized. The cation was 1-(3,5-ditert-butyl-4-hydroxybenzyl)-3-methyl-imidazolium, and the anions were tetrafluoroborates, hexafluorophosphates, and bis(trifluoromethylsulfonyl)imide. The physical properties of the synthetic products and of poly(ethylene glycol) (PEG) with the additive were evaluated. The oxidative stability of 0.5 wt % 1-(3,5-di-tert-butyl-4-hydroxybenzyl)-3-methyl-imidazolium hexafluorophosphates in PEG were assessed via rotating bomb oxidation test (RBOT), thermal analysis, and copper strip test. The tribological behaviors of the additives for PEG application in steel/steel contacts were evaluated on an Optimol SRV-IV oscillating reciprocating friction and wear tester as well as on MRS-1J four-ball testers. The worn steel surface was analyzed by a JSM-5600LV scanning electron microscope and a PHI-5702 multifunctional X-ray photoelectron spectrometer. RBOT test, thermal analysis, and copper strip test results revealed that synthesized ionic liquids possessed excellent antioxidant properties. Tribological application results revealed that these could effectively reduce friction and wear of sliding pairs compared with the PEG films used without the additives. Specifically, (BHT-1)MIMPF(6) exhibited better antiwear properties at an optimum concentration of 1 wt %. At this level, its antiwear property significantly improved by 100 times with respect to using just the PEG base oil. Boundary lubrication films composed of metal fluorides, organic fluorines, organic phosphines, and nitride compounds were formed on the worn surface, which resulted in excellent friction reduction and antiwear performance.

Tribological properties of novel imidazolium ionic liquids bearing benzotriazole group as the antiwear/anticorrosion additive in poly(ethylene glycol) and polyurea grease for steel/steel contacts.

The imidazolium ionic liquids (ILs) bearing benzotriazole group were synthesized and evaluated as antiwear (AW) and anticorrosion additive in poly(ethylene glycol) (PEG) and polyurea grease for steel/steel contacts at room temperature and 150 °C. The physical properties of the synthetic ILs and PEG with the additive were measured. The anticorrosion property of the synthetic ILs was assessed via the accelerated corrosion test and copper strip corrosion test, which reveals the excellent anticorrosion properties in comparison with pure PEG and the selected conventional ILs having no benzotriazole group. Tribological results indicated that these ILs as the additives could effectively reduce friction and wear of sliding pairs in PEG and also in polyurea grease. The tribological properties were generally better than the normally used zincdialkyldithiophosphate-based additive package (T204) in polyurea grease. The wear mechanisms are tentatively discussed according to the morphology observation of worn surfaces of steel discs by scanning electron microscope (SEM) and the surface composition analysis by X-ray photoelectron spectroscopy (XPS).

Functional ionic gels formed by supramolecular assembly of a novel low molecular weight anticorrosive/antioxidative gelator

The present work reports a novel anticorrosive low molecular weight gelator (LMWG) that can self-assemble in normal ILs (II) through collective intermolecular interactions (ion pairing, H-bonding, π–π stacking). The LMWG is structurally imidazolium type “ionic liquid” bearing benzotriazole group. It can gelate ILs via supramolecular assembly to form a fibrous structure. The benzotriazole group endows the anticorrosion and antioxidation property of the gelator. The obtained ionic gels have good conductivity, making them potential anticorrosive solid electrolytes. The anticorrosion and antioxidation together with the thixotropic character also make them potential high performance semi-solid lubricants, especially for some electrical contacts, that can be used at low temperatures and liquify upon mechanical shearing with low friction and good antiwear property.

Core–Shell–Corona-Structured Polyelectrolyte Brushes-Grafting Magnetic Nanoparticles for Water Harvesting

A novel superhydrophilic material, charged polymer brushes-grafted magnetic core-shell-corona composite nanoparticles (Fe3O4@SiO2@PSPMA), was developed to harvest water through the hydration effect. Because of both the strong hydration capability and the good swelling performance, the negatively charged polymer brushes, PSPMA brushes, endow the composite nanoparticles with superhydrophilicity and a good water-absorbing performance like a sponge, while the magnetic Fe3O4 cores allow easy separation of Fe3O4@SiO2@PSPMA nanoparticles with absorbed water from oil/water mixture under an external magnetic field. The functional particles have the capability of harvesting water droplets whether floating on an oil surface or in the oil. This water-absorbing material uses selective wettability to harvest water and achieve oil-water separation and may be useful in finding novel approaches for recycling water from sewage and removing water in the petroleum industry.

Anticorrosion imidazolium ionic liquids as the additive in poly(ethylene glycol) for steel/Cu–Sn alloy contacts

3-((1H-benzo[d][1,2,3]triazol-1-yl)methyl)-1-methyl-1H-imidazolium hexafluorophosphates ([BTAMIM][PF6]) ionic liquids (ILs) were evaluated as friction reduction, antiwear (AW) and anticorrosion additives in poly(ethylene glycol) (PEG) for steel/Cu-Sn alloy contacts at 100 degrees C. The physical properties of PEG with the additive were measured. The anticorrosion properties of [BTAMIM][PF6] was assessed via the accelerated corrosion test, which reveals the excellent anticorrosion properties in comparison with selected conventional ILs that have no benzotriazole group. Tribological results indicated that [BTAMIM][PF6] as additives could effectively reduce the friction and wear of sliding pairs in PEG. The tribological properties were generally better than the normally used dibutyl phosphite (T304) and conventional ILs L-P108 in PEG. The wear mechanisms are tentatively discussed according to the morphology observation of worn surfaces of Cu-Sn alloy discs by scanning electron microscopy (SEM) and surface composition analysis by X-ray photoelectron spectroscopy (XPS), which revealed complex tribochemical reactions during the sliding process leading to a surface protective film composed of [Cu(-C6H5N3-R)], Cu20, CuF2 and C-O bond containing compound is formed. A strong interaction between benzotriazole and the surface of the Cu alloy was proposed to account for the excellent friction reduction, anti-wear and anti-corrosion capability improvement.

Thermoreversible Gel Lubricants through Universal Supramolecular Assembly of a Nonionic Surfactant in a Variety of Base Lubricating Liquids

The present paper investigates a new type of thermoreversible gel lubricant obtained by supramolecular assembly of low-molecular-weight organic gelator (LMWG) in different base oils. The LMWG is a nonionic surfactant with polar headgroup and hydrophobic tail that can self-assemble through collective noncovalent intermolecular interactions (H-bonding, hydrophobic interaction) to form fibrous structures and trap base oils (mineral oils, synthetic oils, and water) in the as-formed cavities. The gel lubricants are fully thermoreversible upon heating-up and cooling down and exhibit thixotropic characteristics. This makes them semisolid lubricants, but they behave like oils. The tribological test results disclosed that the LMWG could also effectively reduce friction and wear of sliding pairs compared with base oils without gelator. It is expected that when being used in oil-lubricated components, such as gear, rolling bearing, and so on, gel lubricant may effectively avoid base oil leak and evaporation loss and so is a benefit to operation and lubrication failure for a long time.

Charged Polymer Brushes-Grafted Hollow Silica Nanoparticles as a Novel Promising Material for Simultaneous Joint Lubrication and Treatment

The fabrication of core/shell charged polymer brushes-grafted hollow silica nanoparticles (PSPMA-g-HSNPs) is reported. Because of the excellent hydration capability of the shells consisting of charged polymer brushes, the functional nanoparticles can achieve a good lubricating effect in aqueous media via hydration lubrication mechanism. The mesoporous hollow silica cores endow the nanoparticles with drug loading-release capability. Aspirin, as a useful drug for treating arthritis, was employed to carry out in vitro drug loading and release studies. It is clear that brushes-modified hollow silica exhibited long-term drug release performance. The combination of lubrication and drug loading capabilities results in the great clinical potential of new multifunctional nanoparticles as injectable joint lubricant fluid in arthritis treatment.

Candle Soot as Particular Lubricant Additives

An onion-like carbon material was prepared from candle soot, and its tribological properties as an additive were investigated in water. The material assumed a spherical shape with a layered nanostructure based on high-resolution transmission electron microscopic analysis and had considerable sp2 hybrid carbon as revealed by Raman spectroscopy. The tribological properties were determined on an optimal SRV-IV oscillating reciprocating friction and wear tester. The results indicate that these candle soots as additives are able to effectively reduce both the friction and wear of sliding pairs in water. In addition, the chemical reactivity, physical stability, surface charge, and size of candle soot had a key impact on their lubrication properties. Based on our characterization of the wear scars by scanning electron microscopy and in situ Raman spectroscopy, we suggest a rolling and sliding lubrication mechanism.

Switching friction with thermal- responsive gels.

The thermosensitive graphene oxide (GO)/poly(N-isopropyl acrylamide) (pNIPAM) composite hydrogels are prepared, and their tribological properties in response to external stimuli are evaluated. The frictional coefficient of the hydrogels is closely related to the gel composition and ambient temperature. When the gel is in swelling state below the low critical solution temperature (LCST), it shows ultra-low friction and exhibits high friction at a shrunk state above the LCST. The huge difference of frictional coefficient under two states can be reversibly switched many times by altering the temperature. The incorporation of a nonthermal sensitive monomer into pNIPAM could change the LCST and thus the transformation point of frictional coefficient can be altered. These reversible and tunable frictional hydrogels have potential application in the design of intelligent control equipment.

Slip flow of diverse liquids on robust superomniphobic surfaces

Water slips exist over superhydrophobic solid surfaces, but the slip flow of diverse liquids on a single surface has not been deliberately studied to date. Here, we report the slip flow behavior of a variety of liquids with different surface tensions and viscosities on a robust omniphobic surface. This surface displayed a dramatic slippage effect and thus a high drag reduction efficiency of approximately 10-20% for all liquids, depending on both liquid viscosity and surface energy. The observed liquid slip was attributed to the surface dual micro/nanostructure and the low-surface-energy coating.