Modification of POSS and their tribological properties and resistant to space atomic oxygen irradiation as lubricant additive of multialkylated cyclopentanes

Developing functional additive resistant to space atomic oxygen(AO)irradiation through simple molecular design and chemical synthesis to enhance the lubricating performance of multialkylated cyclopentanes(MACs)oil is a significant challenge.Herein,sulfur-containing polyhedral oligomere silsesquioxane(POSS)were synthesize via a click-chemistry reaction of octavinyl polyhedral oligomeric with alkyl sulfide.The reduce-friction(RF),anti-wear(AW)properties and anti-AO irradiation of POSS-S-R as MACs base oil additives in atmospheric and simulated space environments were systematically investigated for the first time.Results demonstrate that POSS-S-R not only possesses outstanding anti-AO irradiation capacity but also effectively improves the RF and AW of MACs in atmospheric or simulated space surroundings.This improvement is due to the excellent anti-AO irradiation properties of the POSS structure itself and the high load-carrying ability of silicon-containing and sulfur-containing compounds generated by tribo-chemical reactions,which effectively separates the direct contact of the friction interface.We believe that this synthesized POSS-S-R is a promising additive for space lubricants.

Interfacial mechanism of hydrogel with controllable thickness for stable drag reduction

Surface wettability plays a significant role in reducing solid–liquid frictional resistance,especially the superhydrophilic/hydrophilic interface because of its excellent thermodynamic stability.In this work,poly(acrylic acid)-poly(acrylamide)(PAA–PAM)hydrogel coatings with different thicknesses were prepared in situ by polydopamine(PDA)-UV assisted surface catalytically initiated radical polymerization.Fluid drag reduction performance of hydrogel surface was measured using a rotational rheometer by the plate–plate mode.The experimental results showed that the average drag reduction of hydrogel surface could reach up to about 56%in Couette flow,which was mainly due to the interfacial polymerization phenomenon that enhanced the ability of hydration layer to delay the momentum dissipation between fluid layers and the diffusion behavior of surface.The proposed drag reduction mechanism of hydrogel surface was expected to shed new light on hydrogel–liquid interface interaction and provide a new way for the development of steady-state drag reduction methods.

A novel polyionic liquid with lubricity and viscosity-increasing dual functionalities as the additive in aqueous lubrication system

The polyionic liquid poly-PEGMA-r-METAC(PPM)with quaternary ammonium has been synthesized and evaluated as additive in aqueous lubricating fluids.The rheological behavior of aqueous lubricating fluids with PPM has been characterized to confirm PPM’s function as a viscosity modifier.The tribological behavior of aqueous lubricating fluids with PPM has been investigated on SRV-V and MTM testing machines.It was found that PPM has excellent viscosity-increasing,lubricating,and anti-wear properties as an additive for aqueous,which can be attributed to the ability of PPM to form the protective film and boundary tribofilm generated from complex tribochemical reaction on rubbing surface.The obtained PPM with dual functions of anti-corrosion additives and viscosity index improver can play an important role in diverse lubrication regimes.

超分子凝胶润滑材料的研究进展

开发高性能润滑材料对于降低摩擦磨损带来的能量损失,以及避免严重的机械故障和关节损伤均具有重要意义.超分子凝胶润滑材料可以实现对液体润滑剂的高效捕获,因其良好的触变性能,解决了传统润滑材料易爬移、泄漏及润滑效率低等问题.超分子凝胶润滑材料具有性能动态可调和可逆相转变等特点,使其具有发展为智能润滑材料的天然优势.通过功能化设计可以赋予超分子凝胶润滑材料减摩、抗磨、抗腐蚀、自修复及高承载能力等特性,在机械润滑和生物润滑领域均表现出潜在的应用前景.本文综述了基于不同液体润滑剂(润滑油、水及离子液体)的超分子凝胶润滑材料的发展现状,并讨论了其在不同润滑领域的发展前景.

Fluorinated graphene quantum dots with long-term lubrication for visual drug loading and joint inflammation therapy

Osteoarthritis(OA)treatment mainly relies on developing new drugs or nanocarriers,while little attention is paid to building novel remedial mode and improving drug loading efficiency.This work reports an integrated nanosystem that not only realizes visual drug loading and release,but also achieves enhanced lubrication and effective joint inflammation therapy based on fluorinated graphene quantum dots(FGQDs).Oxygen introduction promotes FGQDs outstanding water-stability for months,and layered nano-sized structure further guarantees excellent lubricating properties in biomimetic synovial fluid.The special design of chemistry and structure endows FGQDs robust fluorescence in a wide range of pH conditions.Also,the excitation spectrum of FGQDs well overlaps the absorption spectrum of drugs,which further constructs a new concept of internal filtering system to visually monitor drug loading by naked eyes.More importantly,extraordinary long-term lubrication performance is reported,which is the first experimental demonstration of concentration-dependent mutations of coefficient of friction(COF).Cell incubation experiments indicate that drug-loaded FGQDs have good biocompatibility,tracking property of cellular uptake and drug release,which show efficient anti-inflammation potential for H2O2-induced chondrocyte degradation by up-regulated cartilage anabolic genes.This study establishes a promising OA treatment strategy that enables to monitor drug loading and release,to enhance long-time lubricating property,and to show effective anti-inflammatory potential for cartilage protection.

Tribochemical synthesis of functionalized covalent organic frameworks for anti-wear and friction reduction

Tribochemistry can be defined as a field dealing with the chemical reactions occurring in the friction zone,capable of catalyzing mechanical and physico-chemical changes in the friction contact area,facilitating the formation of tribo-films,which is also an efficient approach to fabricate novel innovative materials.In this paper,we report the successful synthesis of the silicon oil(SO)-functionalized covalent organic frameworks(COFs)prepared via the tribochemical method when subjected to the reciprocating friction;during the friction process,the rich aldehyde-terminated COFs can bond with amino SO via the Schiff base reaction between aldehyde group and amino group to obtain the desired functionalized COFs(SO@COF-LZU1).The tribochemical reaction progress was tracked through in-situ monitoring of the friction coefficient and the operating conditions during the entire friction process.Noticeably,the friction coefficient continued to decrease until it finally stabilized as the reaction progressed,which revealed the formation of a protective tribo-film.Herein,an approximate tribochemical model was presented,wherein the reaction mechanism was investigated and analyzed by employing structural analysis techniques like magic angle spinning nuclear magnetic resonance(MAS NMR),transmission electron microscopy(TEM),and X-ray photoelectron spectroscopy(XPS).Furthermore,the tribochemical-induced SO@COF-LZU1 exhibited remarkable tribological performance with a low friction coefficient of 0.1 and 95.5%reduction in wear volume when used as additives of 500SN base oil.The prime focus of our research was on the preparation and functionalization of COF materials via tribochemical reactions,unraveling a new avenue for the rational design and preparation of functional materials.

Stable dispersibility of bentonite-type additive with gemini ionic liquid intercalation structure for oil-based drilling

In this study,the direct intercalation of gemini ionic liquids(ILs)with different alkyl chains into the bentonite(BT)interlayer as a high-performance lubricating additive for base oil 500SN was investigated.The purpose of modifying BT with an IL is to improve the dispersion stability and lubricity of BT in lubricating oil.The dispersibility and tribological properties of IL–BT as oil-based additives for 500SN depend on the increase in interlamellar space in BT and improve as the chain length is increased.More importantly,the IL–BT nanomaterial outperforms individual BT in improving wear resistance,owing to its sheet layers were deformed and sprawled in furrows along the metal surface,thereby resulting in low surface adhesion.Because of its excellent lubrication performance,IL-modified BT is a potential candidate for the main component of drilling fluid.It can be used as a lubricating additive in oil drilling and oil well construction to reduce equipment damage and ensure the normal operation of equipments.

Lignin composite ionic liquid lubricants with excellent anti-corrosion,anti-oxidation,and tribological properties

A new type of lubricating material(BTA-P_(4444)-Lig)was synthesized by combining lignin with tetrabutylphosphorus and benzotriazole.The tribological properties,corrosion resistance,and anti-oxidation properties of BTA-P_(4444)-Lig as a lubricant were investigated.The lubricating material exhibits excellent friction reduction and wear resistance,as well as good thermal stability and excellent oxidation resistance.Mechanistic analysis reveals that the active elements N and P in the lubricating material react with the metal substrate,and the reaction film effectively blocks direct contact between the friction pairs,affording excellent friction reduction and wear resistance.At the same time,the phenolic hydroxyl group in lignin reacts with oxygen free radicals to form a resonance-stable semi-quinone free radical,which interrupts the chain reaction and affords good anti-oxidant activity.

Oil-soluble ionic liquids as antiwear and extreme pressure additives in poly-α-olefin for steel/steel contacts

To enhance the lubricating and extreme pressure(EP) performance of base oils, two types of oil-soluble ionic liquids(ILs) with similar anion albeit dissimilar cations were synthesized. The physical properties of the prepared ILs were measured. The anticorrosion properties of ILs were assessed by conducting corrosion tests on steel discs and copper strips, which revealed the remarkable anticorrosion properties of the ILs in comparison with those of the commercial additive zinc dialkyldithiophosphate(ZDDP). The tribological properties of the two ILs as additives for poly-α-olefin-10(PAO10) with various mass concentrations were investigated. The tribological test results indicate that these ILs as additives are capable of reducing friction and wear of sliding contacts remarkably as well as enhance the EP performance of blank PAO10. Under similar test conditions, these IL additives exhibit higher lubricating and anti-wear(AW) performances than those of ZDDP based additive package in PAO10. Subsequently, X-ray photoelectron spectroscopy(XPS) and energy dispersive spectrometer(EDS) were conducted to study the lubricating mechanism of the two ILs. The results indicate that the formation of tribochemical film plays the most crucial role in enhancing the lubricating and AW behavior of the mixture lubricants.

Physicochemical and tribological properties of gemini-type halogen-free dicationic ionic liquids

A series of new halogen-free dicationic ionic liquids(ILs)with different alkyl chain lengths were prepared,and the relationship between the alkyl chain length,physicochemical and tribological properties of ILs,and their role as neat lubricant for steel–steel friction pairs,was investigated.Evaluation of stability during hydrolysis and copper strip corrosion test results show that synthetic ILs are stable and not corrosive to metal contacts,due to the halogen-free anions.The friction and wear test results indicate that ILs with long alkyl chains have excellent friction-reducing and anti-wear properties,especially at high temperatures.Based on the surface three-dimensional(3D)profiles,electrical contact resistance,scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDS),and the X-ray photoelectron spectrometry(XPS)analysis of the worn surfaces of steel discs,we can conclude that the efficiency of ILs is due to the formation of high quality tribofilms that consist of both tribochemical reaction and ordered absorption films.

Constructing a biomimetic robust bi-layered hydrophilic lubrication coating on surface of silicone elastomer

Silicone elastomers-based materials have been extensively involved in the field of biomedical devices,while their use is extremely restricted due to the poor surface lubricity and inherent hydrophobicity.This paper describes a novel strategy for generating a robust layered soft matter lubrication coating on the surface of the polydimethylsiloxane(PDMS)silicone elastomer,by entangling thick polyzwitterionic polyelectrolyte brush of poly(sulfobetaine methacrylate)(PSBMA)into the sub-surface of the initiator-embedded stiff hydrogel coating layer of P(AAm-co-AA-co-HEMA-Br)/Fe,to achieve a unified low friction and high load-bearing properties.Meanwhile,the stiff hydrogel layer with controllable thickness is covalently anchored on the surface of PDMS by adding iron powder to provide catalytic sites through surface catalytically initiated radical polymerization(SCIRP)method and provides high load-bearing capacity,while the topmost brush/hydrogel composite layer is highly effective for aqueous lubrication.Their synergy effects are capable of attaining low friction coefficient(COFs)under wide range of loaded condition in water environment with steel ball as sliding pair.Furthermore,the influence of mechanical modulus of the stiff hydrogel layer on the lubrication performance of layered coating is investigated,for which the COF is the lowest only when the modulus of the stiff hydrogel layer well matches the PDMS substrate.Surprisingly,the COF of the modified PDMS could remain low friction(COF<0.05)stably after encountering 50,000 sliding cycles under 10 N load.Finally,the surface wear characterizations prove the robustness of the layered lubricating coating.This work provides a new route for engineering lubricious silicon elastomer with low friction,high load-bearing capacity,and considerable durability.

Effective sugar-derived organic gelator for three different types of lubricant oils to improve tribological performance

In this study,the gelling ability and lubrication performance of N-octadecyl-D-gluconamides(NOG)in liquid paraffin(LP),pentaerythritol oleate(PE-OA),and polyethylene glycol(PEG)oils were systemically investigated.The NOG,which could gelate the investigated oils,was successfully synthesized by a one-step method.The prepared gel lubricants were completely thermoreversible and exhibited improved thermal stability,according to the thermogravimetry analysis(TGA)reports.Rheological tests confirmed that the NOG gelator could effectively regulate the rheological behavior of the base oils.Tribological evaluation suggested that NOG,as an additive in the three types of base oils,could remarkably reduce the friction and wear in steel contacts.A plausible mechanism for the improved performances was proposed based on the mechanical strength of the gels and the formation of the boundary-lubricating film on the worn surface.The results indicated that NOG is a potential gelator for preparing gel lubricants with excellent tribological properties and environment-friendly characteristics.

Fibers reinforced composite hydrogels with improved lubrication and load-bearing capacity

Hydrogels as one kind of soft materials with a typical three-dimensional(3D)hydrophilic network have been getting great attention in the field of biolubrication.However,traditional hydrogels commonly show poor tribology performance under high-load conditions because of their poor mechanical strength and toughness.Herein,pure chemical-crosslinking hydrogels mixed with different types of the micron-scale fibers can meet the requirements of strength and toughness for biolubrication materials,meanwhile the corresponding tribology performance improves significantly.In a typical case,three kinds of reinforcement matrix including needle-punched fibers,alginate fibers,and cottons are separately combined with Poly(n-vinyl pyrrolidone)-poly 2-hydroxyethyl methacrylate(PVP-PHEMA)hydrogels to prepare fibers reinforced composite hydrogels.The experimental results show that the mechanical properties of fibers reinforced composite hydrogels improve greatly comparable with pure PVP-PHEMA hydrogels.Among three kinds of fibers reinforced composite hydrogel,the as-prepared composite hydrogels reinforced with needle-punched fibers possess the best strength,modulus,and anti-tearing properties.Friction tests indicate that the fibers reinforced composite hydrogels demonstrate stable water-lubrication performance comparable with pure PVP-PHEMA hydrogels.Besides,the hydrogel-spunlace fiber samples show the best load-bearing and anti-wear capacities.The improved tribology performance of the composite hydrogels is highly related to mechanical property and the interaction between the fibers and hydrogel network.Finally,spunlace fibers reinforced hydrogel materials with high load-bearing and low friction properties are expected to be used as novel biomimetic lubrication materials.