Search Results (19)

Water-based lubricants (WBLs) are increasingly being considered for electrified drivetrain applications; however, their electrochemical stability toward bearing steels remains insufficiently understood. This study evaluated the corrosion behavior of through-hardened AISI 52100 bearing steel in novel WBLs to elucidate the corrosion kinetics and surface degradation mechanisms. Round steel disks were cleaned and tested in 50 wt% aqueous dilutions of glycerol, ethylene glycol (MEG), polyethylene glycol (PEG), and polyalkylene glycol (PAG). Electrochemical measurements were conducted using a three-electrode cell in accordance with ASTM G3-14, employing open circuit potential (OCP), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization curves. Among the uninhibited fluids, DI water exhibited the highest corrosion current density (19.85 µA/cm²), while glycerol- and PEG-based systems showed the lowest values (0.79 and 0.85 µA/cm², respectively), attributed to organic adsorption at the steel/electrolyte interface. EIS analysis revealed a single charge-transfer-controlled process across all fluids, consistent with a weak, non-passive interfacial oxide whose protective character is modulated by organic adsorption. The addition of NaNO₃ produced divergent effects depending on the base fluid chemistry: the corrosion activity was reduced in DI water and glycerol systems through enhanced passivation, while PEG- and PAG-based formulations showed increased corrosion current densities and reduced charge transfer resistance, attributed to competitive disruption of the polymer boundary layer by nitrate ions. Surface characterization by SEM/EDAX and white-light interferometry corroborated the electrochemical findings, revealing fluid-dependent corrosion morphologies ranging from uniform attack in DI water to localized pitting in polymer-based systems, with NaNO₃ shifting the corrosion mode in PEG/PAG systems from localized to combined localized and uniform attack. These findings highlight the critical role of fluid chemistry in controlling corrosion processes in water-based lubricants and provide mechanistic insight for the development of corrosion-stable formulations for high-performance electrified drivetrain applications. Full article

Objectives: Topical lubricants are the fundamental treatment for dry eye disease (DED). However, the molecular mechanisms underlying their efficacy remain unknown. Here, the protective effects of Thealoz^® Duo with 3% trehalose and 0.15% hyaluronic acid are investigated in DED patients by a longitudinal clinical study and subsequent elucidation of the tear proteome and cell signaling changes. Methods: Participants were classified as moderate to severe DED (DRY, n = 35) and healthy (CTRL, n = 23) groups. Specific DED subgroups comprising evaporative (DRYlip) and aqueous-deficient with DRYlip (DRYaqlip) were also classified. Only DED patients received Thealoz^® Duo. All participants were clinically examined before (day 0, T1) and after the application of Thealoz^® Duo at day 28 (T2) and day 56 (T3). Next, 174 individual tear samples from all groups at three time-points were subjected to proteomics analysis. Results: Clinically, Thealoz^® Duo significantly improved the ocular surface disease index at T2 vs. T1 (DRY, p = 1.4 × 10⁻²; DRYlip, p = 9.2 × 10⁻³) and T3 vs. T1 (DRY, p = 2.1 × 10⁻⁵; DRYlip, p = 1.2 × 10⁻⁴), and the tear break-up time at T3 vs. T1 (DRY, p = 3.8 × 10⁻²; DRYlip, p = 1.4 × 10⁻²). Thealoz^® Duo significantly ameliorated expression of inflammatory response proteins (p < 0.05) at T3, which was observed at T1 (DRY, p = 3.4 × 10⁻⁴; DRYlip, p = 7.1 × 10⁻³; DRYaqlip, p = 2.7 × 10⁻⁸). Protein S100-A8 (S100A8), Alpha-1-antitrypsin (SERPINA1), Annexin A1 (ANXA1), and Apolipoprotein A-I (APOA1) were found to be significantly reduced in all the DED subgroups. The application of Thealoz^® Duo showed the therapeutic characteristic of the anti-inflammatory mechanism by promoting the expression of (Metalloproteinase inhibitor 1) TIMP1 in all the DED subgroups. Conclusions: Thealoz^® Duo substantially improved the DED symptoms and restored the functionality of the tear lipid layer to near normal in DRYlip and DRY patients by ameliorating inflammation. Notably, this study unravels the novel mechanistic alterations underpinning the healing effects of Thealoz^® Duo in DED subgroups in a time-dependent manner, which supports the improvement in corresponding clinical attributes. Full article

Ionic liquid molecules exhibit a variety of properties that are well suited for use as lubricants or additives for lubricants, since they form tribolayers that reduce friction and wear. As additives in the design of new water-based biolubricants, ionic liquids present the advantages of polar nature to use in aqueous lubrication, whilst being biocompatible and with null toxicity, opening up the opportunity to develop novel biolubricants. Choline is a cation present in numerous ionic liquids and is widely recognized for its water solubility, biodegradability, low toxicity, and role as a green solvent in different applications. This work presents the comparative studies of several water-based biolubricants and thin-layer films on stainless steel using a low proportion of Choline-based ionic liquids. The results of friction and wear using water-based biolubricants with 1 wt% of different Choline-based ionic liquids showed good tribological performance. In addition, Choline Lysinate, an amino-acid ionic liquid which is biocompatible, nontoxic, and biodegradable, presented excellent performance and was used as a precursor of thin-layer films on stainless steel showing outstanding behavior in pin-on-disc configuration and sapphire/stainless-steel contacts. Subsequent X-ray photoelectron spectroscopy confirmed the presence of a tribolayer containing the amino acid compound on the metallic surface. Full article

Oxidized carbon nanohorn (CNHox) a carbon nanomaterial that has attracted attention due to its unique material properties. It is expected to be applied in various areas like cancer treatment, gene-expression technology, fluids with high thermal conductivity, lubricants, and so on. While the rheological measurements of suspensions provide information on the effective size and interactions of suspended particles, the rheological behaviors of aqueous suspensions of CNHox have never been systematically investigated. To clarify the rheological behaviors of aqueous suspensions of CNHox, their viscosity and dynamic viscoelasticity were measured with changing particle concentration and salt concentration. The viscosity of a CNHox suspension showed yield stress at low shear rates and showed shear-thinning behavior with increasing shear rates. The viscosity of 5 weight % CNHox suspensions was comparable to that of 60 weight % silica suspensions. This high viscosity at a low CNHox concentration is probably due to the porous structure and large effective volume of the CNHox particle. The estimated effective volume of CNHox calculated by the Krieger−Dougherty equation was 18.9 times larger than the actual volume calculated by the mass concentration and density. The dependence of rheological behavior of the CNHox suspension on salt concentration was weak compared to that of the colloidal silica suspension. This weak dependence on salt concentration may be due to the roughness of the particle surface, which would weaken the effect of electric double-layer interactions and/or van der Waals interactions between particles. These rheological behaviors of the aqueous suspension of CNHox shown in this research will be useful in efforts to improve the efficiency of its utilization for the various applications. Full article

Punctal occlusion (PO) is considered to improve both tear-film instability and increased friction during blinking and may consequently affect blinks. The purpose of this study was to investigate the effect of PO on blinks. This study involved 16 eyes of 16 severe aqueous deficient dry eye (ADDE) patients (mean age: 65.7 years). In all eyes, tear meniscus radius (TMR), spread grade (SG) of the tear-film lipid layer (i.e., SG 1-5: 1 being the best), fluorescein break-up time (FBUT), corneal epithelial damage score (CED), conjunctival epithelial damage score, corneal filament (CF) grade, lid-wiper epitheliopathy (LWE) grade, and superior limbic keratoconjunctivitis (SLK) grade were evaluated at before and at more than 1-month after PO. Moreover, using a custom-made high-speed blink analyzer, palpebral aperture height, blink rate, upper-eyelid closing-phase amplitude/duration/maximum velocity, and upper-eyelid opening-phase amplitude/duration/maximum velocity were measured at the same time point. After PO, TMR, SG, FBUT, CED, and the CF, LWE, and SLK grades were significantly improved, and upper-eyelid opening/closing-phase amplitude and maximum velocity significantly increased (all p < 0.04). The findings of this study suggest that PO improves ocular surface lubrication and that blink-related parameters can reflect the friction that occurs during blinking in eyes with severe ADDE. Full article

The ocular surface is covered by a tear film consisting of an aqueous/mucin phase and a superficial lipid layer. Mucins, highly O-glycosylated proteins, are responsible for lubrication and ocular surface protection. Due to contact lens wear or eye disorders, lubrication of the ocular surface can be affected. Artificial glycopolymers which mimic natural mucins could be efficient in ophthalmic therapy. Various neutral, positively, and negatively charged mucin-mimicking glycopolymers were synthesized (n = 11), cultured in different concentrations (1%, 0.1%, and 0.01% w/v) with human corneal epithelial cells (HCE), and analyzed by various cytotoxicity/viability, morphology, and immunohistochemistry (IHC) assays. Six of the eleven glycopolymers were selected for further analysis after cytotoxicity/viability assays. We showed that the six selected glycopolymers had no cytotoxic effect on HCE cells in the 0.01% w/v concentration. They did not negatively affect cell viability and displayed both morphology and characteristic markers as untreated control cells. These polymers could be used in the future as mucin-mimicking semi-synthetic materials for lubrication and protection of the ocular surface. Full article

The performance of plastic components in water-bearing parts of industrial and household appliances, often in the presence of harsh environments and elevated temperatures, critically relies on the mechanical and thermal polymer stability. In this light, the precise knowledge of aging properties of polymers formulated with dedicated antiaging additive packages as well as various fillers is crucial for long-time device warranty. We investigated and analysed the time-dependent, polymer-liquid interface aging of different industrial performance polypropylene samples in aqueous detergent solution at high temperatures (95 °C). Special emphasis was put on the disadvantageous process of consecutive biofilm formation that often follows surface transformation and degradation. Atomic force microscopy, scanning electron microscopy, and infrared spectroscopy were used to monitor and analyse the surface aging process. Additionally, bacterial adhesion and biofilm formation was characterised by colony forming unit assays. One of the key findings is the observation of crystalline, fibre-like growth of ethylene bis stearamide (EBS) on the surface during the aging process. EBS is a widely used process aid and lubricant enabling the proper demoulding of injection moulding plastic parts. The aging-induced surface-covering EBS layers changed the surface morphology and promoted bacterial adhesion as well as biofilm formation of Pseudomonas aeruginosa. Full article

Owing to their low cost and environmentally friendly nature, water-based lubricants have benefits over oil-based ones. However, the appropriate additive package is indispensable in improving its tribological properties. In the current study, we have investigated the friction and wear reduction ability of bis(2-hydroxyethyl) ammonium oleate protic ionic liquid (PIL) in a glycerol aqueous lubricating fluid. The tribo-tests were performed using a ruby–steel friction pair acting in reciprocation mode. The coefficient of friction and wear were the main characteristics of the evaluation. Analysis of the physical properties of the investigated lubricating samples and worn surface analysis were performed to reveal a more detailed picture. The study shows that the investigated PIL can significantly reduce friction and wear. The most suitable concentration of PIL was 0.5%, where friction and wear were reduced 2.6 and 15.8 times, respectively. Using the investigated PIL facilitates a sliding coefficient of friction as low as 0.039. It was hypothesized that the formation of the adsorption layer and metal soap was responsible for this. Further studies could be directed toward higher load and speed applications. Full article

Three diprotic ionic liquids (PILs) containing bis(2-hydroxyethyl) ammonium cations and citrate (DCi), lactate (DL), or salycilate (DSa) hydroxy/carboxylate anions were studied as lubricants for Ti6Al4V–sapphire contact. At room temperature, the neat PILs are non-Newtonian fluids, which show up to a 70% friction coefficient reduction with respect to water. New aqueous lubricants were developed using PILs as 1 wt.% additives in water. The new (Water + 1 wt.% PILs) lubricants showed friction reductions of higher than 50% with respect to water at room temperature. The lowest friction coefficients at room temperature were achieved with thin lubricant layers deposited on Ti6Al4V using Water + 1 wt.% PIL after water evaporation. At 100 °C, the best tribological performance, with the lowest friction coefficients and wear rates, was obtained for the PILs containing aliphatic anions: DCi, and DL. The surface layers of the sapphire balls with mild adhesion and abrasion wear mechanisms were observed via scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). Full article

In the present work, Black Phosphorus Quantum Dots (BPQDs) were synthesized via sonication-assisted liquid-phase exfoliation. The average size of the BPQDs was 3.3 ± 0.85 nm. The BPQDs exhibited excellent dispersion stability in ultrapure water. Macroscale superlubricity was realized with the unmodified BPQDs on rough Si₃N₄/SiO₂ interfaces. A minimum coefficient of friction (COF) of 0.0022 was achieved at the concentration of 0.015 wt%. In addition, the glycerol was introduced to promote the stability of the superlubricity state. The COF of the BPQDs-Glycerol aqueous solution (BG_aq) was 83.75% lower than that of the Glycerol aqueous solution (G_aq). Based on the above analysis, the lubrication model was presented. The hydrogen-bonded network and silica gel layer were formed on the friction interface, which played a major role in the realization of macroscale superlubricity. In addition, the adsorption water layer could also prevent the worn surfaces from making contact with each other. Moreover, the synergistic effect between BPQDs and glycerol could significantly decrease the COF and maintain the superlubricity state. The findings theoretically support the realization of macroscale superlubricity with unmodified BPQDs as a water-based lubrication additive. Full article

Phospholipids and hyaluronan are two key biomolecules that contribute to the excellent lubrication of articular joints. Phospholipids alone and in combination with hyaluronan have also displayed low friction forces on smooth surfaces in micro- and nanosized tribological contacts. In an effort to develop aqueous-based lubrication systems, it is highly relevant to explore if these types of molecules also are able to provide efficient lubrication of macroscopic tribological contacts involving surfaces with roughness larger than the thickness of the lubricating layer. To this end, we investigated the lubrication performance of hyaluronan, the phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and mixtures of these two components using glass surfaces in a mini-traction machine. We compared our data with those obtained using flat silica surfaces in previous atomic force microscopy studies, and we also highlighted insights on hyaluronan–phospholipid interactions gained from recent simulations. Our data demonstrate that hyaluronan alone does not provide any lubricating benefit, but DPPC alone and in mixtures with hyaluronan reduces the friction force by an order of magnitude. Full article

Understanding the effects of electrical double layers (EDL) and tribo-induced electric fields on the electroosmotic behaviors of lubricants is important for developing high-performance water-based lubricants. In this study, EDL conductivities of aqueous lubricants containing a surfactant of 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS) or cetyltrimethylammonium bromide (CTAB) were analyzed. The interfacial zeta potentials of the synthesized lubricants and Al₂O₃ ceramic-alloy steel contacts were measured, and frictional potentials of ceramic and steel surfaces were determined using a modified ball-on-disc configuration. The distribution characteristics of the tribo-induced electric field of the ceramic-steel sliding contact were numerically analyzed. The electroosmotic behaviors of the lubricants were investigated using a four-ball configuration. It was found that an EDL and tribo-induced electric field was a crucial enabler in stimulating the electroosmosis of lubricants. Through altering EDL structures, CHAPS enhanced the electroosmosis and penetration of the water-based lubricant, thus resulting in improved lubrication. Full article

In this study, graphene oxide (GO) nanoflakes and lithium salt (LiPF₆) were utilized as lubrication additives in ether bond−containing dihydric alcohol aqueous solutions (DA(aq)) to improve lubrication performances. The apparent friction reduction and superlubricity were realized at the Si₃N₄/sapphire interface. The conditions and laws for superlubricity realization have been concluded. The underlying mechanism was the synergy effect of GO and LiPF₆. It was proven that a GO adsorption layer was formed at the interface, which caused the shearing interface to transfer from solid asperities to GO interlayers (weak interlayer interactions), resulting in friction reduction and superlubricity realization. In addition to the GO adsorption layer, a boundary layer containing phosphates and fluorides was formed by tribochemical reactions of LiPF₆ and was conducive to low friction. Additionally, a fluid layer contributed to friction reduction as well. This work proved that GO−family materials are promising for friction reduction, and provided new insights into realizing liquid superlubricity at macroscale by combining GO with other materials. Full article

Hydration lubrication has emerged as a new paradigm for lubrication in aqueous and biological media, accounting especially for the extremely low friction (friction coefficients down to 0.001) of articular cartilage lubrication in joints. Among the ensemble of molecules acting in the joint, phosphatidylcholine (PC) lipids have been proposed as the key molecules forming, in a complex with other molecules including hyaluronic acid (HA), a robust layer on the outer surface of the cartilage. HA, ubiquitous in synovial joints, is not in itself a good boundary lubricant, but binds the PC lipids at the cartilage surface; these, in turn, massively reduce the friction via hydration lubrication at their exposed, highly hydrated phosphocholine headgroups. An important unresolved issue in this scenario is why the free HA molecules in the synovial fluid do not suppress the lubricity by adsorbing simultaneously to the opposing lipid layers, i.e., forming an adhesive, dissipative bridge between them, as they slide past each other during joint articulation. To address this question, we directly examined the friction between two hydrogenated soy PC (HSPC) lipid layers (in the form of liposomes) immersed in HA solution or two palmitoyl–oleoyl PC (POPC) lipid layers across HA–POPC solution using a surface force balance (SFB). The results show, clearly and surprisingly, that HA addition does not affect the outstanding lubrication provided by the PC lipid layers. A possible mechanism indicated by our data that may account for this is that multiple lipid layers form on each cartilage surface, so that the slip plane may move from the midplane between the opposing surfaces, which is bridged by the HA, to an HA-free interface within a multilayer, where hydration lubrication is freely active. Another possibility suggested by our model experiments is that lipids in synovial fluid may complex with HA, thereby inhibiting the HA molecules from adhering to the lipids on the cartilage surfaces. Full article

In this study, we use an aqueous solution synthesis method to prepare silver perrhenate powders and suspend them into a poly alpha olefin (PAO) base oil with polyoxyethylene octylphenyl ether. Four ball tests and ball-on-disk reciprocating mode are performed to determine how silver perrhenate performs tribologically as a lubricating additive over a wide range of temperatures. The physical and chemical properties, as well as the lubricating mechanisms of the silver perrhenate additive, are characterized via X-ray diffraction, scanning electron microscope, Fourier transformation infrared spectroscopy, Raman spectrum, and X-ray photoelectron spectroscopy. The four-ball test results demonstrate that the oil added with silver perrhenate additive is more effective than the base oil in reducing friction and improving wear resistance, and provides the best lubricating performance when at a concentration of 0.5 wt%. The reciprocating mode findings indicate that the hybrid lubricant exhibits distinctively better tribological properties than the base oil at high temperatures, and its low shear strength and chemical inertness allow for low friction at elevated temperatures. The resulting silver perrhenate layer that incorporates native superalloy oxides on the worn surface can provide lubrication by serving as a barrier that prevents direct contact between the rubbing surfaces at elevated temperatures. Full article