Water-based Lubricant Research Articles

Rheological properties of water-based amino acid ionic liquids

The rheological properties and zero-shear viscosity of water-based lubricants (WBLs) containing amino acid ionic liquids (AAILs) were investigated using both equilibrium (EMD) and non-equilibrium molecular dynamics (NEMD) simulations. We also performed experimental measurements to validate the simulations. The simulations demonstrated that adding AAIL additives to water increased both the shear viscosity and zero-shear viscosity. We added tetrabutylphosphonium (P4444) as a cation and three different amino acids, serine (Ser), lysine (Lys), or phenylalanine (Phe), as anions. We varied the AAIL concentration from 5 to 10 wt. % for tetrabutylphosphonium-serine (P4444-Ser) ionic liquid additives, showing that AAILs increased water viscosity by 68%–125%, depending on concentration. The P4444-Ser WBLs also exhibited a significantly higher first normal stress difference than water, meaning they could support more load in lubrication. The improved rheology persisted over a wide range of shear rates up to ∼1011 s−1. We have extracted full rheological parameters by fitting data into Cross, Carreau–Yasuda, and Eyring models, including zero-shear viscosity and critical shear rates of onset shear thinning. The experimental values of zero-shear viscosity were close to zero-shear viscosity results obtained from fitting NEMD results to these models, demonstrating the high fidelity of the molecular model. We explored the formation of hydration shells around amino acid anions as a marker for low friction behavior. These findings suggest that AAIL WBLs can be potentially low-friction and biodegradable lubricants in tribological applications.

Versatile Pickering emulsion gel lubricants stabilized by cooperative interfacial graphene oxide-polymer assemblies.

Although a large number of water- and oil-based gel lubricants have found extensive potential applications in industrial and biomedical fields, developing new-type emulsion-based gel lubricants that may effectively integrate their characteristics and preponderances remains a significant challenge. Here a water-in-oil Pickering emulsion gel lubricant that is able to combine the high colloidal stability of traditional Pickering emulsions, the good swelling and corrosion resistance of oil-based gel lubricants, and the high cooling capacity of water-based gel lubricants prepared from a binary mixture of aqueous graphene oxide (GO) dispersion and diamino-functionalized polydimethylsiloxane oil solution in a broad concentration, pH, and water volume fraction range is reported. It can provide favourable lubrication for the Si3N4/steel and Si3N4/silicone tribopairs either in air or under water owing to the formation of a sturdy adsorbed oil film and ball-bearing actions of the GO particles. It can also be printed into various colourful 2D and 3D geometries upon direct extrusion into water, thanks to its water-in-oil nature and inherent shear-thinning and thixotropic properties, which further shows good prospects in underwater operations and artificial biomimetic organs. Our study may provide new insights into the design and preparation of novel semi-solid materials for diverse industrial, engineering, and biomedical applications.

Rheological Characterization and Tribological Evaluation of Water-Based Lubricants in AISI 52100 Bearing Steel

This study explores the rheological and tribological behavior of water-based lubricants (WBLs) as potential alternatives for electric vehicle (EV) applications. As the transportation sector increasingly shifts towards EVs to reduce carbon emissions, the demand for efficient lubricants becomes critical. WBLs here are defined as fluids containing a minimum of 50 wt% water mixed with glycerol, ethylene glycol (MEG), polyethylene glycol (PEG), or one of two polyalkylene glycols (PAGs). Rheological properties were investigated and compared with traditional lubricating oils. Results demonstrate distinctive rheological characteristics in WBLs, with viscosity–temperature responses resembling traditional oils with lowered pressure–viscosity coefficients. Nevertheless, WBLs exhibit promising film-forming capabilities in highly loaded contacts. Additionally, in sliding contacts, WBLs generally display lower friction coefficients compared to traditional oils, with PEG exhibiting the lowest value near 0.1. These findings suggest that WBLs may offer advantages in reducing friction and energy loss in EV applications. Furthermore, sliding wear tests indicate low wear rates in WBLs such as PEG, PAG, and glycerol, supporting their potential as viable lubrication options. The study highlights the importance of high-pressure rheology and tribochemistry in wear mechanisms among the different lubricants.

Study on pH-dependence of electroosmosis effect and tribological behavior of water-based lubricants at friction interfaces

pH is usually used to assess the corrosion resistance and bacteriostasis of lubricants. In this paper, the electroosmotic and tribological characteristics of water-based lubricants at AISI 52100 steel/alumina ceramic friction interfaces are evaluated as an effect of pH value. A self-excited electric field (SEEF) generated by interface material frictional electrification induces the lubricant electroosmosis. Appropriately increasing the pH can improve the electroosmotic abilities of lubricants by changing the electrical double layer (EDL) structures at the friction material/lubricant interfaces. The lubricant tribological performance and penetrability are improved upon increasing the pH from 7 to 10. This is attributed to the fact that the lubricant with favorable electroosmotic performance shows a better penetrability, thus exerting an excellent effect of anti-friction and anti-wear.

In-situ gelation based on rapid crosslinking: A versatile bionic water-based lubrication strategy

Hydrogel is emerging as a new water-based lubricant due to its enhanced load-bearing capacity and lubrication effect in industrial process and biological application. But the loss and degradation issues in long-term usage become a bottleneck for its further development. Hence how to realize the continuous supplement of hydrogel lubricant in the friction process with an instant response to shear stress becomes a highly expected goal. In this study, inspired by the regeneration of cartilage, a surface engineering strategy is first put forward based on chemically active interface and cross-linking gelation, in which Borax as cross-linking agent is released in-situ with the grinding debris in friction process from polyimide/Borax composite coating into the polyvinyl alcohol (PVA) solution, followed with instant gelation to form effective lubrication mediate layer between contact interface. The combined experimental and molecular dynamics simulation studies suggest that the enhanced intermolecular interaction in hydrogel layer which highly depends on cross-linking degree, together with hydrodynamic effect is responsible for the excellent lubrication and high adaptability to various working condition even under the high contact stress of 175.90 MPa. The similar tribological performances in other chemically active interface-fluid combination systems demonstrate the versatility of this facile strategy.

Fabrication of Zwitterionic Polymer-Functionalized Onion-like Carbon Nanoparticles as Aqueous Lubricant Additives.

Onion-like carbon (OLC) is a kind of carbon material with a graphene-like structure and large interlayer spacing, favorable to a good lubricating performance. Herein, a facile method is presented for the preparation of functionalized OLC nanoparticles from candle soot with surface modification. The OLC nanoparticles are collected from combustion soot with candle burning via a simple heat treatment, and then the zwitterionic polymer (polyethylenimine-quaternized derivative, PEIS) can self-assemble onto the OLC surface with epigallocatechin gallate via Michael addition and Schiff-base reaction, thus obtaining PEIS-functionalized OLC nanoparticles (PEIS@OLC). The grafting zwitterionic polymer PEIS endows the OLC nanoparticles with good hydrophilic performance, so the as-obtained PEIS@OLC exhibits outstanding dispersion and lubricating property as a water-based lubricant additive. Compared to pure water, the average coefficient of friction decreases to 0.110 from 0.512, and the corresponding wear volume is reduced by 61.02% with 1.5 wt % addition. The improved lubricating property is mainly due to the synergetic effect of the protective film induced by the tribochemical reaction and the hydration film of zwitterionic polymer PEIS. Besides, the OLC nanoparticles could also display the nanoscale rolling and repairing effects at the friction contact interface, resulting in reduction of friction and wear.

Tribological properties of Sargassum carbon dots as additives in water-based lubricants

This study evaluated the tribological characteristics of a novel eco-friendly water-based lubricant containing carbon dots (CDs) obtained from Sargassum as additives. The mean friction coefficient of a lubricant containing 5 mg/ml CD contents was 78 % lower than that of pure water. Furthermore, a correlation between wear rate, contact shape, and kinetic vertical ball displacement was also established.

Tribological performance of a surfactant derived from its structure of molecular aggregates in water

Surfactants are promising additives for water-based lubricant surfaces due to their ability to adsorb on metal surfaces and reduce friction under boundary lubrication. In this study, the aggregation behavior of surfactants in aqueous solutions and their effects on friction and anti-wear properties were investigated using sodium 2-hexyldecanoate (2HDNa) as an example. The results revealed that 2HDNa forms vesicles at low concentrations and transits to micelles at higher concentrations. The presence of vesicles led to a significant reduction in friction coefficient and improved anti-wear properties by forming an absorbed film, which was confirmed by neutron reflectometry (NR). The findings of this study emphasize the lubrication and anti-wear performance of vesicles and the importance of surfactant concentration control in water-based lubrication.

Response to Letter to the Editor on "A randomized trial on the effectiveness and safety of 5 water-based personal lubricants".

Response to Letter to the Editor on "A randomized trial on the effectiveness and safety of 5 water-based personal lubricants".

Tribological performance and lubrication mechanism of carbon nitride nanosheets as novel and high-efficiency additives for water lubrication

Recently, water-based nano-additives have attracted more attention with the resurrection of water lubrication owing to the increasing awareness of environmental protection and energy-saving. Highly water-dispersible carbon nitride nanosheets (C3N4 nanosheets), obtained via a high-yield and low-cost hydrothermal approach, were first used as a novel and environmentally-friendly nano-additive for water-based lubrication. The tribotest results exhibited that the tribological performances of C3N4 nanosheets in the water-based lubricant are highly sensitive to their adding concentrations. It was found that a C3N4 nanosheet concentration of 0.2 wt% could decrease the friction and wear in steel-steel contacts by 49.0% and 54.2%, respectively. The lubrication performances of C3N4 nanosheets as additives were much better than those of C3N4, attributed to their regular shape, good water dispersibility, and high reactivity. In addition, C3N4 nanosheets as additives exhibited a long service life even under harsh lubrication conditions. In addition, the molecular dynamics (MD) simulation technique was first employed to study the lubrication performances and lubrication regimes of C3N4 nanosheets. By combining the results of MD simulations and wear track surface analyses, the formation of water-based lubricating film and tribochemical film (mainly composed of organic compounds, metal nitrides, iron oxides, metal carbonates, and C3N4 nanosheets) coupled with the interlayer sliding and polishing effects of C3N4 nanosheets were primarily responsible for the excellent tribological performances of C3N4 nanosheets.

Liquid superlubricity of lubricants containing hydroxyl groups and their aqueous solution under rolling/sliding conditions

Macroscale rolling/sliding conditions are in the superlubricity, a little-studied topic so far. The purpose of this paper is to examine the formation of elastohydrodynamic lubrication (EHL) films by water-based lubricants (glycerol and polyethylene glycol (PEG)), providing superlubricous friction. Experiments were carried out on an optical ball-on-disc tribometer under rolling/sliding conditions. The film thickness was measured by the thin film colorimetric interferometry, and the viscosity of liquids was measured by rotational and high-pressure falling body viscometers. The results show that tribochemical reactions are not the mandatory reason for friction to reach the superlubricity level when using the water-based lubricants. The studied liquids themselves are almost Newtonian. With the addition of water, the signs of shear thinning behavior disappear even more. Suitable conditions for this type of lubricant can be predicted using the known Hamrock–Dowson equations. An anomaly in the thickness of the lubricants was observed as an abrupt change at certain conditions. The more PEG there is in the lubricant, the higher the thickness at the beginning of the jump.

A simple and affordable open-source quantitative tribometric assay and the use thereof for the analysis of a commercial water-based lubricant

Quantitative assessment of biotribological properties requires expensive specialized equipment. The aim was to: i) adapt an open-source load cell-based platform (PASTA) for biotribometric analysis; ii) study the effects of oxidation on the water-based lubricant using PASTA. Water-based lubricant was treated with 2,2'-azobis(2-amidinopropane) dihydrochloride and/or glutathione. The samples were analyzed with the ORP-146S redox microsensor and PASTA using a modified HX711 integrated circuit bord, NodeMCU ESP-32S, and an open-source Python script. PASTA can be adapted for affordable and reliable quantitative biotribometric assessment. Glutathione can prevent the loss of lubrication capacity of a water-based lubricant upon exposure to air.

Cervical sample-taking in the primary health service

In Norway, approximately 360000 cervical screening samples were taken in 2020, of which 11000 were registered as inadequate. We therefore wished to investigate doctors' knowledge of cervical sample-taking in the primary health service. An anonymous survey on cervical sample-taking was sent by email to around 4700 members of the Norwegian College of General Practice in September 2021. Of the 1039 doctors who responded to the survey, 820 (79%) reported that they always indicate the reason for taking the sample in the requisition form, and 898 (86%) reported that they avoid taking a sample during menstruation. Only one in three doctors (343) correctly indicated the location of the squamocolumnar junction in postmenopausal women. In response to a question aimed at users of the ThinPrep method, which is particularly sensitive to sampling errors, 426 out of 697 (61%) answered that they either avoid using a lubricant or use a water-based lubricant, while only 35% of the doctors responded that they stop taking the sample if bleeding occurs. The results show that although many doctors have satisfactory knowledge, a continuous focus on cervical sample-taking is essential. Correct sampling and knowledge of anatomical factors in postmenopausal women may be significant for reducing the number of inadequate samples.

Hydration layer structure modulates superlubrication by trivalent La 3+ electrolytes

Water-based lubricants provide lubrication of rubbing surfaces in many technical, biological, and physiological applications. The structure of hydrated ion layers adsorbed on solid surfaces that determine the lubricating properties of aqueous lubricants is thought to be invariable in hydration lubrication. However, we prove that the ion surface coverage dictates the roughness of the hydration layer and its lubricating properties, especially under subnanometer confinement. We characterize different hydration layer structures on surfaces lubricated by aqueous trivalent electrolytes. Two superlubrication regimes are observed with friction coefficients of 10 −4 and 10 −3 , depending on the structure and thickness of the hydration layer. Each regime exhibits a distinct energy dissipation pathway and a different dependence to the hydration layer structure. Our analysis supports the idea of an intimate relationship between the dynamic structure of a boundary lubricant film and its tribological properties and offers a framework to study such relationship at the molecular level.

A review on tribology, characterization and lubricants for water-based drilling fluids

The challenges associated with drilling large displacement horizontal wells are numerous, and their adverse effects can lead to severe damage or even shut down of the drilling operation. Frictional torque of the tubular column is one of the most common problems encountered when applying water-based drilling fluids to the drilling of extended reach wells. This is because during the drilling process, there is continuous friction between the drilling tool and the rock. When water-based drilling fluid cannot effectively reduce friction, it will cause difficulty in lifting or lowering the drilling tool, resulting in sticking, and thus affecting the drilling operation. Most petroleum engineers use different lubricants to reduce friction and wear during drilling.The purpose of this study is to present the friction and lubrication state during drilling, the mechanism of action of boundary lubrication, lubrication evaluation and analysis methods, and friction reduction and wear resistance related to water-based drilling fluid lubricants reported in literature for reducing friction.Based on the review, we recommend a broad evaluation of lubricants using different lubricity performance evaluation methods to determine the true lubricity performance in the coexistence of multiple frictions during drilling. In addition, we recommend that future researchers enhance the application of numerical simulations in the analysis of lubricant lubrication mechanisms to address the difficulty of direct experiments in boundary lubrication laboratories. Any experimental program requires at least five characterization techniques, including friction coefficient, wear resistance testing, scanning electron microscopy, energy dispersive X-ray spectroscopy, and electron spectroscopy, to provide a detailed understanding of the friction reduction mechanism of the lubricant used. Lubricants based on bionic technology with good water solubility, low biotoxicity, and easy biodegradability are highly encouraged because of their availability and good lubricating properties.

Friction Performance of Self-Emulsifying Esters and Organic Phosphate Esters Mixed Aqueous Solution on the Surface of TB6 Titanium Alloy

Water-based lubrication, due to the poor film-forming ability of water, faces challenges in achieving effective lubrication for titanium alloys. This study systematically investigates the frictional performance of phosphorus-based extreme pressure (EP) additives and self-emulsifying esters (SEE) on the surface of titanium alloy (TB6) under different pressures and temperatures. The core lubricant consists of SEE with nonylphenol polyoxyethylene ether phosphate ester (NPEP), polyoxyethylene oleyl ether phosphate ester (POEP), and alcohol ether phosphate ester (AEP). Results show that SEE significantly improves the film-forming ability of the aqueous solution, while phosphate ester forms a strong chemical adsorption film on the alloy surface via P-O-Ti covalent bonds, enhancing the strength of the lubricating film. The combination of SEE and phosphate esters in the water-based solution enables effective lubrication for titanium alloys. Particularly, the mixture of POEP and SEE demonstrates excellent synergistic effects, making it an ideal blend for water-based cutting fluids for titanium alloys. This study elucidates the lubrication mechanisms and action ranges between different additives, providing important guidance for the development and promotion of water-based cutting fluids.

A Tribological and Electrochemical Study of Protic Ionic Liquid and Bentonite Particles Used as Lubricating Additives in Water-Based Lubricants

A Tribological and Electrochemical Study of Protic Ionic Liquid and Bentonite Particles Used as Lubricating Additives in Water-Based Lubricants

Fabrication of MXene@Fe3O4@PNA composite with photothermal effect as water-based lubricant additive

Improving the tribological performance of water via designing nanomaterials as lubricant additive has garnered mounting interest. In this work, the poly-(N-isopropylacrylamide) microgel is grafted onto Fe3O4 nanoparticles surface (Fe3O4@PNA) via free radical polymerization. Then, the Fe3O4@PNA can self-anchored on the MXene nanosheets via hydrogen bonding interaction to obtain MXene@Fe3O4@PNA composite. The as-prepared MXene@Fe3O4@PNA can effectively reduce friction and wear when used as a water-based lubricant additive. Compared with pure water, the average coefficient of friction (COF) and wear volume decrease by 61% and 78.7%, respectively. The lubrication mechanism was analyzed by focused ion beam technique-TEM (FIB-TEM) and X-ray photoelectron spectroscopy (XPS). The outstanding tribological performance of MXene@Fe3O4@PNA is attributed to the synergistic lubrication effect of MXene and Fe3O4@PNA. Interlayer shear of MXene and spherical Fe3O4@PNA can make MXene@Fe3O4@PNA play a full role of sliding friction and rolling friction mechanism, which can induce tribo-chemical reactions to form a protective film on the contact area of the friction pair. In addition, the hydrophilic groups of the MXene@Fe3O4@PNA can adsorb a large number of water molecules and form a hydration layer, reducing the agglomeration of nanosheets and acting as a boundary lubrication film. Moreover, the as-prepared MXene@Fe3O4@PNA exhibit excellent photothermal conversion performance in both underwater environment and dry state. Based on this characteristic, infrared light can be collected efficiently and stored quickly. Then, convert and utilize it. Therefore, the multifunctional MXene@Fe3O4@PNA has a broad application prospect as a water-based intelligent lubrication additive.

Achieving Greener, Super-Robust Performance Water-Based Lubrication: Obtained by a Multifunctional Ionic Liquid Aqueous System and Formation of Unique Interfacial Interactions

Owing to the green, high-performance, and application-specific work conditions, water-based lubricating systems show unlimited potential for chemical engineering development. The interfacial behavior of functional additives in aqueous systems is complex and variable due to polarity and interfacial activity, thus showing important research significance. Herein, five novel ionic liquids were synthesized; their unique interfacial behavior in the polar water system contributes a lot to the advanced corrosion resistance and the improved extreme pressure-bearing capacity. The polar groups in the molecular structure of ionic liquids can adsorb preferentially in competition with water molecules, resulting in the formation of an adsorption layer with a high elastic modulus on the metal surface. Benefiting from the tribochemical reaction and the strong polar adsorption effect, the tribofilm at the sliding asperity exhibited effective antiscuffing and antiwear performance. Moreover, their characteristic cationic groups enrich the driving force of the molecular self-assembly process and enhance the ability to form ordered molecular aggregates, whose behavior in an aqueous system facilitates super-robust lubricity. This work can promote the in-depth understanding, future design, and optimization of the aqueous lubricating system, providing content enrichment and expansion for the lubrication technology for harsh service conditions.

(024) A Randomized Trial on the Sexual Effectiveness and Impact on the Vaginal Microbiome of Reformulated Personal Water Lubricants with Lowered Osmolality and pH in Premenopausal and Postmenopausal Women

Abstract Introduction Vaginal dryness may be associated with postmenopausal women; however, it may also occur due to chronic medical conditions and as a direct side effect from medications. Personal lubricants can address sexual complaints and symptomatology associated with vaginal dryness, although clinically published data supporting their efficacy remains limited. Age-associated vaginal-physiological changes due to hypoestrogenic milieux include increased pH, decreased natural lubrication, reduced endothelial rugae and altered vaginal microbiome. While personal lubricants may alleviate symptoms, their definitive effects on the vaginal microbiome remain understudied and underappreciated. Objective This study examined reformulated water-based lubricants (lowered osmolalities and pH,) and their effect on female sexual function compared to their counterparts (higher osmolalities/increased pH). A secondary analysis examined if these reformulated lubricants influenced the vaginal microbiome of women from different age groups. Methods An open-label, parallel-design study was performed in heterosexual women in stable monogamous relationships, aged 18–65 years with mild-to-moderate vaginal dryness and dyspareunia. The study population (n=174) included an approximate 50:50 ratio of premenopausal to postmenopausal women. The randomization schedule was stratified by menopausal status. Subjects were randomized to use one of five water-based lubricants and instructed to use their lubricant during vaginal intercourse at least once a week over a 4-week period. The Female Sexual Function Index (FSFI) measured sexual functioning after 4 weeks of use as an indicator of lubricant performance. More than a 4-point increase in total FSFI is deemed clinically important. From the study-enrolled subjects, 50 females were randomized to one of five lubricant treatment groups for secondary microbiome analysis. To this end, four vaginal swabs per participant were sampled during pre- (“baseline”) and post- (“2 hours”, “24 hours” and “4 weeks”) lubricant application to assess bacterial diversity via 16S sequencing. Additionally, vaginal moisture and pH measurements were collected at baseline, 2 hours, and 24 hours post-lubricant application and correlated with microbiome diversity and richness using non-parametric tests and linear mixed models. Results An increase in FSFI total score of >4 points was found for all lubricants in the total population and for 4/5 lubricants in the premenopausal subgroup, as indicated by the mean differences to baseline. The number of subjects in sexual function (total FSFI >26.55) after treatment was significantly greater than the number in sexual function before treatment for both subgroups (premenopausal 19.3% to 78.4%; postmenopausal 22.3% to 75.3%; p<0.0001 for both). Lactobacillus species and Gardnerella vaginalis were the predominant taxa across all participants. Repeated lubricant applications did not alter the vaginal microbiome for up to 4 weeks post-product applications. Microbial diversity and relative abundance differed significantly between age groups but remained unaffected during product applications. Relative abundance of Lactobacilli spp. negatively correlated with vaginal pH while that of Gardnerella spp. showed a positive correlation with vaginal pH across all age groups. Conclusions These reformulated lubricants can be used not only to relieve symptomatology of vaginal dryness and dyspareunia, but to enhance overall sexual satisfaction regardless of menopausal status. These study lubricants demonstrated no significant impact on vaginal microbiome. Further studies with larger samples are warranted. Disclosure Yes, this is sponsored by industry/sponsor: Reckitt Benckiser Health. Clarification: Industry funding only - investigator initiated and executed study. Any of the authors act as a consultant, employee or shareholder of an industry for: Reckitt Benckiser Health.