Water-Based Lubricants: Development, Properties, and Performances

Recent development in friction of supramolecular gel lubricant: from mechanisms to applications

Due to the unique self-assembling structure and rheological properties, supramolecular gel lubricants have become the third major type of liquid lubricating materials to supplement the lubricating oils and greases. The molecular structures of gelators applicable to oil-based, water-based and extreme conditions base oils were summarized firstly. Furthermore, this review aims at exploring the relationships between the molecular structures of gelators and the gel-forming, rheological and tribological properties of gel lubricants. Based on the wide application of gel in various lubrication fields, the synergistic lubricating effect between gel lubricants and nanomaterials, films, textured surfaces were analyzed. The design of solid-liquid composite lubrication systems based on gel lubricants and solid lubricants were attempted to be highlighted and revealed. Finally, the perspectives on the development of gel lubricants and corresponding composite lubricating materials were presented.

Improved properties of hybrid Al-CNTs via h-BNs coated with ag and ni for ball bearings

Ball bearings face numerous challenges under harsh operating conditions of elevated pressure between the balls and other contacting parts of the bearing like drop in tribological properties. To address these challenges, this paper presents the first successful experimental investigation of incorporating an innovative hexagonal boron nitride (h-BN) into Aluminum-Carbon nanotube (Al-0.6 wt% CNTs) nanocomposites. This was achieved using electroless chemical deposition technique to coat the materials with silver (Ag) and nickel (Ni), improving the wettability and dispersion between the matrix and reinforcement. Various h-BN ratios (2, 4, 6, 8 and 10 wt%) are incorporated and consolidated through high-energy ball milling and hot compaction techniques. The produced samples were tested and analyzed physically, mechanically, tribologically, and microstructurally. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses were used to explore the new morphologies and structures. The study delves into density, hardness, and wear resistance. The optimal h-BN content is determined to be 8 wt%, enhancing wettability and dispersion within the Al-CNTs matrix. Thus, the properties of hardness, compressive strength, wear rate, and COF at 8 wt% of h-BN content were enhanced by 105%, 60%, 74.5%, and 78.5%, respectively, compared to pure Al. This is due to the uniform scattering of h-BN nanoparticles across the entire surface, despite a significant decrease in relative density. In conclusion, the combination of mechanical alloying, electroless deposition, and hot compaction techniques proves to be effective in producing Al-CNTs/h-BN nanocomposites coated with Ag and Ni nanoparticles.

Covalent organic frameworks in tribology - A perspective

Two-dimensional covalent organic frameworks (2D COFs) are an emerging class of crystalline porous materials formed through covalent bonds between organic building blocks. COFs uniquely combine a large surface area, an excellent stability, numerous abundant active sites, and tunable functionalities, thus making them highly attractive for numerous applications. Especially, their abundant active sites and weak interlayer interaction make these materials promising candidates for tribological research. Recently, notable attention has been paid to COFs as lubricant additives due to their excellent tribological performance. Our review aims at critically summarizing the state-of-art developments of 2D COFs in tribology. We discuss their structural and functional design principles, as well as synthetic strategies with a special focus on tribology. The generation of COF thin films is also assessed in detail, which can alleviate their most challenging drawbacks for this application. Subsequently, we analyze the existing state-of-the-art regarding the usage of COFs as lubricant additives, self-lubrication composite coatings, and solid lubricants at the nanoscale. Finally, critical challenges and future trends of 2D COFs in tribology are outlined to initiate and boost new research activities in this exciting field.

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.

Fundamental, mechanism and development of hydration lubrication: From bio-inspiration to artificial manufacturing

Friction and lubrication are ubiquitous in all kinds of movements and play a vital role in the smooth operation of production machinery. Water is indispensable both in the lubrication systems of natural organisms and in hydration lubrication systems. There exists a high degree of similarity between these systems, which has driven the development of hydration lubrication from biomimetic to artificial manufacturing. In particular, significant advancements have been made in the understanding of the mechanisms of hydration lubrication over the past 30 years. This enhanced understanding has further stimulated the exploration of biomimetic inspiration from natural hydration lubrication systems, to develop novel artificial hydration lubrication systems that are cost-effective, easily transportable, and possess excellent capability. This review summarizes the recent experimental and theoretical advances in the understanding of hydration-lubrication processes. The entire paper is divided into three parts. Firstly, surface interactions relevant to hydration lubrication are discussed, encompassing topics such as hydrogen bonding, hydration layer, electric double layer force, hydration force, and Stribeck curve. The second part begins with an introduction to articular cartilage in biomaterial lubrication, discussing its compositional structure and lubrication mechanisms. Subsequently, three major categories of bio-inspired artificial manufacturing lubricating material systems are presented, including hydrogels, polymer brushes (e.g., neutral, positive, negative and zwitterionic brushes), hydration lubricant additives (e.g., nano-particles, polymers, ionic liquids), and their related lubrication mechanism is also described. Finally, the challenges and perspectives for hydration lubrication research and materials development are presented.

Preparation of Hydrophilic Hyper-Cross-Linked Polystyrene Nanospheres with Antibacterial for Improved Water Lubrication Performance

The present study utilizes styrene as a raw material to prepare hyper-cross-linked polystyrene nanospheres (HPSs) through the Friedel-Crafts reaction, establishing stable covalent bond structures within the polymer chains. The hydrophilic polystyrene nanospheres─TMA@SHPSs were successfully synthesized via sulfonation and ion exchange reactions, demonstrating exceptional properties in reducing friction and wear. Compared with pure water, the addition of 4.0 wt % TMA@SHPSs results in a 62.2% reduction in the friction coefficient, accompanied by a significant decrease to 1.17 × 105 μm3 in wear volume. The results demonstrate that TMA@SHPSs, as water-based lubrication additives, generate composite protective films (tribo-chemical protective films and physical protective films) during the friction process, which effectively prevents direct contact between the friction pairs and achieves remarkable antifriction and antiwear effects. The results of the antimicrobial activity test indicate that TMA@SHPSs demonstrate exceptional antibacterial efficacy due to the bacteriostatic effect induced by hydration and the bactericidal properties of quaternary ammonium cations.

Unraveling Water-Based Lubrication with Carbon Dots of Asphaltene Origin

Despite the lower toxicity of water-based lubricants over nonrenewable petroleum-based analogues, they face challenges in achieving widespread adoption due to low stability and inadequate friction-reduction performance. To address this, a cost-effective nanoadditive is synthesized by expansive oxidation of asphaltenes to create biocompatible asphaltene-derived carbon dots [(ACDs); 5 nm]. These ACDs exhibit excellent water redispersibility, promoting long-term friction reduction and marking the first use of an asphaltene-based system for friction reduction in water or oil. Even at low loadings (0.2-4.0 wt %), ACDs significantly reduce friction on steel surfaces (>54%) with tribofilm stability surpassing pristine carbon dots, typical carbon-based graphene quantum dots, and inorganic nanomaterials (commercial 5 and 20 nm silica). The ACDs' attributes include high negative zeta potential, considerable water uptake, varied functional groups, biocompatibility, and a nanodisc shape conducive to stable tribofilm formation through effective particle stacking. The scalable synthesis, high yield, and impressive water redispersibility of ACDs position them favorably for commercial water-based lubrication.

Analysis of TiO2 Nanolubricant Influence in Micro Deep Drawing of Stainless Steel SUS301

To improve the quality of products produced from microforming, various nanolubricants have been applied in the field of micromanufacturing in recent years. In this paper, the effects of glycerol-based lubricant containing TiO₂ NPs (NPs) on micro deep drawing (MDD) of austenitic stainless steel (ASS) SUS301 were studied, and the lubrication mechanism involved was discussed. The MDD experiments were conducted with the SUS301 foils under dry, 1, 2, and 4 wt% TiO₂ NP lubrication conditions. The results show that the use of the TiO₂ nanolubricants can significantly improve the quality of the drawn cups in terms of decreased wrinkling and surface roughness. Besides, the concentration of TiO₂ NPs influences lubricity by reducing friction during the MDD process. The peak drawing force is the lowest when 2 wt% nanolubricant is applied, which drops to 72.54 N from 77.38 N under dry conditions. The micro cup drawn under 2 wt% TiO₂ nanolubricant has the best quality among those obtained under all the lubrication conditions. The lubrication mechanisms are derived from the mending effects of TiO₂ NPs and the formation of thin lubricant films associated with the open lubricant pockets (OLPs) and close lubricant pocket (CLPs) theory in the MDD. The CLPs function as reservoirs that retain lubricants to counteract the load pressure, whereas the OLPs lead to lubricant leakage due to the higher flow resistance. It was found that the lubricant film and NPs are insufficient at a low concentration (1 wt%), while the lubrication performance can be enhanced with increased NP concentration. However, there exist apparent agglomerations on the surface of the produced micro cup when using 4 wt% nanolubricant, which greatly deteriorates the lubricant performance in the MDD process. It is concluded that the lubricant containing 2 wt% TiO₂ NPs demonstrates the best lubrication performance during the MDD of ASS SUS301.

Preparation and characterization of polyethylene glycol/chitosan composite water-based wound healing lubricant

The proportion of pregnant women giving birth through cesarean section is increasing annually worldwide. However, post-cesarean section scar diverticulum is a common condition that occurs and requires better surgical strategies than the methods currently used. We hypothesized that using biological lubricant topically on the incision area during C-section could be an option to minimize the scar. This water-based polyethylene glycol (PEG)/chitosan (CS) composite lubricant was prepared via ultrasonic blending. The product was characterized using scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman spectroscopy. The thermal stability of the materials and their heat absorption and release during heating were analyzed using thermogravimetric analysis and differential scanning calorimetry. Tribological tests proved that the PEG/CS composite had a better lubrication effect than either the PEG or CS lubricant alone, and the cell viability experiments verified that it had good biocompatibility. Finally, application of the composite lubricant onto the backs of mice modeling full-thickness skin incisions further confirmed that the product improved both the re-epithelialization and the collagen levels of the wounded skin. In conclusion, we expect our newly formulated PEG/CS composite lubricant to be useful not only for managing post-cesarean section scar diverticulum but also for healing skin wounds in general.

Development of Doped Carbon Quantum Dot-Based Nanomaterials for Lubricant Additive Applications

The development of advanced lubricants is essential for the pursuit of energy efficiency and sustainable development. In order to improve the properties of lubricating fluids, high-performance lubricating additives are required. In recent research studies, carbon nanomaterials such as fullerenes, carbon nanotubes, and graphene have been examined as lubricating additives to water or oil. Lubricating oils are well known for the presence of additives, especially friction-reducers and anti-wear additives. As part of this work, we have studied the advancement in the research and development of carbon dot (CD)-based lubricant additives by presenting a number of several applications of CD-based additives. We have also highlighted the friction-reducing properties and anti-wear properties of CDs and their lubrication mechanism along with some challenges and future perspectives of CDs as an additive. CDs are carbon nanomaterials that are synthesized from single-atom-thick sheets containing a large number of oxygen-containing functional groups; they have gained increasing attention as friction-reducing and antiwear additives. CDs have gradually been revealed to have exceptional tribological properties, particularly acting as additives to lubricating base oils. In our final section, we discuss the main challenges, future research directions, and a number of suggestions for a complete functionalized or hybrid doped CD-based material.

The Twelve Principles of Green Tribology: Studies, Research, and Case Studies—A Brief Anthology

Sustainability has become of paramount importance, as evidenced by the increasing number of norms and regulations concerning various sectors. Due to its intrinsic trans-sectorial nature, tribology has drawn the attention of the supporters of sustainability. This discipline allows the environmental, economic, and social impacts to be decreased in a wide range of applications following the same strategies. In 2010, Nosonovsky and Bhushan drew up 12 approaches based on the 12 principles of green chemistry and the 12 principles of green engineering, defining the “12 principles of green tribology.” This review exploits the 12 principles of green tribology to fathom the developed research related to sustainability and tribology. Different approaches and innovative studies have been proposed in this short selection as references to consider for further development, pursuing the efforts of the scientific community for a sustainable future through the contribution also of tribosystems. The manuscript aims to provide practical examples of materials, lubricants, strategies, and technologies that have contributed to the overall progress of tribology, decreasing wear and friction and increasing efficiency, and at the same time promoting sustainable development, lowering toxicity, waste production, and loss of energy and resources.

Friction and Wear Properties of a Nanoscale Ionic Liquid-like GO@SiO2 Hybrid as a Water-Based Lubricant Additive

In this study, a nanoscale ionic liquid (NIL) GO@SiO2 hybrid was synthesized by attaching silica nanoparticles onto graphene oxide (GO). It was then functionalized to exhibit liquid-like behavior in the absence of solvents. The physical and chemical properties of the synthesized samples were characterized by means of a transmission electron microscope, X-ray diffraction, Fourier transform infra-red, Raman spectroscopy, and thermogravimetric analysis. The tribological properties of the NIL GO@SiO2 hybrid as a water-based (WB) lubricant additive were investigated on a ball-on-disk tribometer. The results illustrate that the NIL GO@SiO2 hybrid demonstrates good dispersity as a WB lubricant, and can decrease both the coefficient of friction (COF) and wear loss.

Effects of an Electrical Double Layer and Tribo-Induced Electric Field on the Penetration and Lubrication of Water-Based Lubricants

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.

Friction and Wear Characteristics of Aqueous ZrO2/GO Hybrid Nanolubricants

Aqueous nanolubricants containing ZrO2 nanoparticles, graphene oxide (GO) nanosheets, or hybrid nanoparticles of ZrO2 and GO were formulated using a cost-effective ultrasonication de-agglomeration method. The friction and wear characteristics of these water-based nanolubricants were systematically investigated using a block-on-ring testing configuration with a stainless- and alloy steel contact pair. The concentrations and mass ratios of nanoadditives were varied from 0.02 to 0.10 wt.% and 1:5 to 5:1, respectively, to obtain optimal lubrication performance. The application of a 0.06 wt.% 1:1 ZrO2/GO hybrid nanolubricant resulted in a 57% reduction in COF and a 77% decrease in wear volume compared to water. The optimised ZrO2/GO hybrid nanolubricant was found to perform better than pure ZrO2 and GO nanolubricant in terms of tribological performance due to its synergistic lubrication effect, which showed up to 54% and 41% reductions in friction as well as 42% and 20% decreases in wear compared with 0.06 wt.% ZrO2 and 0.06 wt.% GO nanolubricants. The analysis of wear scars revealed that using such a ZrO2/GO hybrid nanolubricant yielded a smooth worn surface, with 87%, 45%, and 33% reductions in Sa compared to water and 0.06 wt.% ZrO2 and 0.06 wt.% GO nanolubricants. The superior tribological performance can be ascribed to the combination of the rolling effect of ZrO2 nanoparticles and the slipping effect of GO nanosheets.

Effect of ultrasonication on lubrication performance of cellulose nano-crystalline (CNC) suspensions as green lubricants

Industrial lubricants are widely introduced to the mechanical systems to reduce the wear and energy losses. With the increasing demand for environmental protection, developing eco-friendly lubricants becomes more crucial. Due to their abundance, biodegradability, non-toxicity, high thermal stability and low cost, cellulose nanocrystals (CNCs) may be an appropriate choice for formulating green lubricants. In this study, using different microstructural and tribological characterization methods, we systematically investigated the effect of ultrasonic treatment on lubrication performance of CNC aqueous suspensions. It was observed that within sonication energy of 4-50 kJ/g_CNC, there exists an optimum condition for tribological measurements. In comparison to the unsonicated suspensions, sonicated CNC lubricants could decrease COF (coefficient of friction) and wear by almost 25 and 30% respectively. Results of this study suggest that ultrasonication processing can significantly improve lubrication performance of CNC aqueous suspensions.

A Comprehensive Review of Water-Based Nanolubricants

Applying nanomaterials and nanotechnology in lubrication has become increasingly popular and important to further reduce the friction and wear in engineering applications. To achieve green manufacturing and its sustainable development, water-based nanolubricants are emerging as promising alternatives to the traditional oil-containing lubricants that inevitably pose environmental issues when burnt and discharged. This review presents an overview of recent advances in water-based nanolubricants, starting from the preparation of the lubricants using different types of nanoadditives, followed by the techniques to evaluate and enhance their dispersion stability, and the commonly used tribo-testing methods. The lubrication mechanisms and models are discussed with special attention given to the roles of the nanoadditives. Finally, the applications of water-based nanolubricants in metal rolling are summarised, and the outlook for future research directions is proposed.