Polymer Lubricant Research Articles

Synergistic effects of nitrogen-containing functionalized copolymer and silicon-doped DLC for friction and wear reduction

We present a strategy to enhance the tribological performances of diamond-like carbon (DLC) films based on synergistic chemical modifications in the polymer lubricant additives and in the carbon film. Our experiments revealed that the polymer functionalization with nitrogen-containing groups and the DLC doping with silicon atoms result in significant friction and wear reduction under severe boundary lubrication conditions. Atomic Force Microscopy revealed the formation of a lubricious tribofilm. Ab initio calculations highlighted the key role of N-Si interactions in promoting the polymer chemisorption on the film, which represents the first, essential step for the tribofilm formation. Our findings suggest that targeted chemical modifications in lubricants and films can substantially advance the tribological performances of DLC films for various industrial applications.

Buoyancy-driven micropolar ternary hybrid nano-suspension within an oblique incinerator-shaped chamber: Thermal and second law analyses

Since performance of thermal systems may depend on fluids’ thermal conductivities being utilized as coolants, improvement of thermal efficiencies of fluids having micro-structures and involving ternary hybrid nanomaterials may be highly valued. In fact, microrotation of ternary hybrid nanofluids (THNFs) in oblique incinerator-shaped chamber may find applications in industrial processes involving polymeric solutions and lubricants where they help in reduction of drag forces and act as better cooling agent. In view of this, the present study carries out thermal and second law dissection of micropolar THNF within an oblique incinerator-shaped chamber heated from bottom emplacing a roundish heater under a fixed heat flux. The THNF comprises of Al2O3, CNT and graphene as nanoparticles. The study reveals that streamlines and isotherms undergo prominent change due to inclination of the chamber. When Raleigh number and diameter of heater amplify streamlines, microrotations, and entropy generation intensify while average Bejan number whittles down. Average heat transfer rate ameliorates by 4.54 % and 2.17 % when total volume fraction augments from 1.5 % to 3 % and 3 %–4.5 %, respectively. Heat transfer rate reduces by 1.23 %, 0.48 %, 3.33 %, 5.24 %, 2.07 %, and 1.66 % when inclination angle increases from 0° to 90° with inclination angle step 15°.

Wear of alumina-PTFE against brass and aluminum: Role of interfacial films and tribochemistry

PTFE matrix composites reinforced with α-Al2O3 fillers are considered a gold standard polymeric solid lubricant. α-Al2O3 PTFE exhibits ultra-low wear rates (k ∼10−8 mm3/Nm) when sliding against steel in the presence of water vapor. Mechanochemical interactions involving the breaking of PTFE chains, and subsequent oxidation in the presence of water vapor helps promote growth of interfacial films that are strongly bound to the sliding interface. In the absence of moisture, wear rates of α-Al2O3 PTFE can increase by as much as three orders of magnitude, underscoring its importance to ultra-low wear behavior. A similar increase in wear rates of α-Al2O3 PTFE in humid environments has recently been observed when sliding against brass counter surfaces, though reasons for this increase remain unclear. These findings suggest that mechanisms of ultra-low wear not only rely on ambient humidity but are also strongly dependent on the counter surface chemistry. In the present work, we test the hypothesis that counter surface chemistry drives alumina PTFE wear by systematically investigating the wear of an α-Al2O3 PTFE composite against brass and aluminum substrates within the context of the morphological and mechanochemical evolution of the sliding interface. Wear tests are conducted under reciprocating, dry sliding conditions. Results presented in this work offer insights on mechanochemical mechanisms that drive wear of α-Al2O3 PTFE against brass and aluminum, and provide a framework for developing strategies for controlling wear.

Bioinspired Bottlebrush Polymers Effectively Alleviate Frictional Damage Both In Vitro and In Vivo.

Bottlebrush polymers (BB) have emerged as compelling candidates for biosystems to face tribological challenges, including friction and wear. This study provides a comprehensive assessment of an engineered triblock BB polymer's affinity, cell toxicity, lubrication, and wear protection in both in vitro and in vivo settings, focusing on applications for conditions like osteoarthritis and dry eye syndrome. Results show that the designed polymer rapidly adheres to various surfaces (e.g., cartilage, eye, and contact lens), forming a robust, biocompatible layer for surface lubrication and protection. The tribological performance and biocompatibility are further enhanced in the presence of hyaluronic acid (HA) both in vitro and in vivo. The exceptional lubrication performance and favorable interaction with HA position the synthesized triblock polymer as a promising candidate for innovative treatments addressing deficiencies in bio-lubricant systems.

Tribological and Mechanochemical Properties of Nanoparticle-Filled Polytetrafluoroethylene Composites under Different Loads.

For the tribological properties of nanoparticle-modified PTFE, a more comprehensive study has been conducted, but there is still some room for research on tribology behavior, tribofilm formation and structure evolution of polytetrafluoroethylene (PTFE) filled with α-Al2O3 and SiO2 nanoparticles during sliding against steel counterparts under different loads. At the same time, it establishes the linkage and mechanism between the maintenance of mechanical strength and the tribological application of polymers in service and provides corresponding scientific data and theoretical guidance for the long-lasting application of polymer lubrication materials. It is found that both composites exhibit good wear resistance across the pressure of 1 MPa to 10 MPa, with the α-Al2O3/PTFE composite demonstrating better performance stability compared to the SiO2/PTFE composite. The high wear resistance is attributed to the formation of tribofilms at the friction interface. For the α-Al2O3/PTFE, an island-like tribofilm is formed with a thickness ranging from 100 to 200 nm, while the tribofilm of the SiO2/PTFE composite is thinner, measuring approximately 50 to 100 nm, and manifests a striped pattern. The chemical composition, both at the surface and subsurface levels, as well as the morphology of the tribofilms, were studied using FTIR spectrometry, X-ray photoelectron spectroscopy (XPS), and FIB-TEM. It is found that the difference in thickness and microstructure of the tribofilms for the two composites is mainly due to the tribochemistry of the nanoparticles. The α-Al2O3 nanoparticle plays a "cohesion" role during the formation of the tribofilm, which facilitates the formation of a thicker, more uniform, and stronger adhered tribofilm on the metallic counterpart, making it more robust against higher shear stress.

Study on the lubrication behavior of low molecular weight poly(vinyl chloride‐co‐n‐butyl acrylate‐co‐vinyl acetate) ternary copolymer in rigid PVC

AbstractHerein, low molecular weight poly(vinyl chloride‐co‐n‐butyl acrylate‐co‐vinyl acetate) (PCBV) ternary copolymers with varied copolymer composition was employed as a novel polymeric lubricant in rigid PVC. The lubrication effect of PCBVs on the melting process and mechanical properties of the final PVC products were fully investigated. The results indicated that PCBV can serve either as an internal or as an external lubricant depending on its composition. PCBV‐45.5 terpolymer (PBA% ~ 45.5%) exhibits outstanding balance both internal and external lubricating roles. SEM‐EDS results show that addition PCBV‐45.5 form a film on the surface of PVC grains as similar as that adding both internal and external lubricants. Fusion characteristics and DMTA demonstrate that PCBV‐45.5 prolongs the fusion time (26% extension, 1.5 phr) and reduces the glass transition temperature (4.0 °C, 1.5 phr). Finally, the mechanical properties of rigid PVC have been greatly improved by using 1.5 phr PCBV‐45.5. In detail, the tensile strength increased from 54 to 59 MPa and the elongation at break increased from 10% to 30%, respectively. Meanwhile, the impact strength of PVC/PCBV‐45.5 is 3.6 times that of the blend without addition. The excellent performance of PCBV exhibited great potential as a polymeric lubricant candidate in rigid PVC composites.

Modeling polymeric lubricants with non-linear stress constitutive relations

Modeling polymeric lubricants with non-linear stress constitutive relations

A high-temperature resistant and high-density polymeric saturated brine-based drilling fluid

Three high-temperature resistant polymeric additives for water-based drilling fluids are designed and developed: weakly cross-linked zwitterionic polymer fluid loss reducer (WCZ), flexible polymer microsphere nano-plugging agent (FPM) and comb-structure polymeric lubricant (CSP). A high-temperature resistant and high-density polymeric saturated brine-based drilling fluid was developed for deep drilling. The WCZ has a good anti-polyelectrolyte effect and exhibits the API fluid loss less than 8 mL after aging in saturated salt environment at 200 °C. The FPM can reduce the fluid loss by improving the quality of the mud cake and has a good plugging effect on nano-scale pores/fractures. The CSP, with a weight average molecular weight of 4804, has multiple polar adsorption sites and exhibits excellent lubricating performance under high temperature and high salt conditions. The developed drilling fluid system with a density of 2.0 g/cm3 has good rheological properties. It shows a fluid loss less than 15 mL at 200 °C and high pressure, a sedimentation factor (SF) smaller than 0.52 after standing at high temperature for 5 d, and a rolling recovery of hydratable drill cuttings similar to oil-based drilling fluid. Besides, it has good plugging and lubricating performance.

Unraveling Tribochemistry and Self-Lubrication Mechanism of Polytetrafluoroethylene by Reactive Coarse-Grained Molecular Dynamics Simulations.

Lubrication of polymeric materials generally involves processes of atomic-scale chemical bond forming/breaking at the interface and mesoscale chain reorientation, disentanglement, and so forth. However, it is difficult to describe the important aspects of tribochemical reactions by conventional coarse-grained molecular dynamics (CGMD) simulations. Here, reactive CGMD simulations were conducted based on the ReaxFF force field to study the tribochemical interactions between polytetrafluoroethylene (PTFE) and iron. The chemical bond forming/breaking between the molecular chain and countersurface was fitted through the bond dissociation energies of specific reaction sites from all-atom ReaxFF-MD simulations. This enabled a quantitative description of tribochemical reactions in a macromolecule system. First, the number of anchoring bonds between PTFE molecules and the countersurface showed a strong correlation with the friction coefficient. The shearing process induced breaking of the interfacial anchoring bonds as well as chain disentanglement in the matrix, which consequently led to ordering reorientation of molecular chains toward sliding direction and hence decrease of friction. Second, two competitive factors were clarified to affect polymer friction with varying temperatures. The decrease of interfacial anchoring reactivity and molecular chain mobility at low temperature prohibited reorientation of molecular chains and increased the friction coefficient. On the other hand, the hardening of PTFE and the reduction in effective contact area at low temperatures decreased the friction coefficient. This led to a turning point with a maximum friction coefficient around 100 K. These results shed light on the essential role of tribochemical reactions on polymer lubrication, especially under low temperatures, which provides design guidance of polymeric lubrication systems for engineering applications.

Development of a Laboratory-Scale Test Methodology for Performance Evaluation of Lubricants for Hot Stamping of an Aluminium Alloy

In hot stamping of aluminium, the need for efficient methods to evaluate, compare, and rank lubricants based on their tribological performance is critical in the early stages of selection. Pilot and simulative testing can be costly, time-consuming, and complex, making it inefficient for initial benchmarking. This work aims to develop a test methodology to assess lubricant performance for hot stamping under key operating conditions without fully simulating the forming process. The proposed method distinguishes the impact of temperature on lubricant degradation, friction, wear response, and cleanability. The tests utilised a conventional hot work tool steel and a 6010S aluminium alloy with two commercially available lubricants: a polymeric lubricant and a lubricant containing graphite. The tribological tests involved a reciprocating, sliding flat-on-flat configuration at two temperatures (100 °C and 300 °C). The methodology showed that the graphite-containing lubricant exhibited over a four times lower friction coefficient than the polymer-based lubricant at 10 wt.% concentration and 300 °C. At 100 °C, both lubricants provide lubrication and can be cleaned, but increasing temperature led to a significant decline of both aspects. The observed temperature range where the lubricants degrade was between 120 °C and 170 °C.

Polymer Lubrication: Pressure–Viscosity–Temperature Dependence of Film Thickness for Highly Loaded Compliant Contacts in Elastohydrodynamic Lubrication Regime

Abstract The relevance of the compliant contacts operated in elastohydrodynamic lubrication regime has increased during the last decades. Polymers and elastomers have been preferred because of their low-cost production or their tribological performance in many mechanical and bioengineering applications, where the metals originally dominated. Especially, in high-performance applications, such as polymer gears, the current subject of interest covers the transition between Piezoviscous-elastic and Isoviscous-elastic regimes of elastohydrodynamic lubrication. Here, it is necessary to precisely determine operating conditions and lubricant properties such as rheology whose contribution to film thickness formation may be influenced by attributes of individual lubrication regimes. The high-pressure viscosimeter and the optical tribometer were used, the former to establish the pressure–viscosity–temperature relationship of two reference lubricants, natural Squalane and synthetic tri(2-ethylhexyl) trimellitate, and the latter to determine the central and minimum film thickness in the circular contact between the PMMA disc and the steel ball using the optical chromatic interferometry method. Experimental results of film thickness demonstrated a significant deviation from the soft elastohydrodynamic lubrication (EHL) models, independently of the lubricant used, load, entrainment speed, and temperature because the pressure–viscosity–temperature response of lubricant was not included. Due to this, film thickness data were regressed, and new power coefficients of dimensionless parameter G¯ were derived. Outcomes confirmed the operation of the compliant circular contact in the transition region between the Piezoviscous-elastic and Isoviscous-elastic regimes with the minimum film thickness identified on the side lobes of the horseshoe shape.

Significance of nanoparticles aggregation and Coriolis force on the dynamics of Prandtl nanofluid: The case of rotating flow

A comparative study is provided by this article with rotational Prandtl host fluid flux of aggregated nano particles and non aggregated nano particles on linear stretching surface. Along with the chemical species diffusion, Arrhenius activation energy is examined. The nano particles thats are playing vital role in modern technology like heat exchange, electronics and material sciences are incorporated because of enhancing heat transmission. The current analysis has significant applications in rolling and manufacturing of polymer sheet, lubrication processes, crystal growing, polymer industry, biomedical and polymer industry. By applying similarity transformation to mathematical formulation based upon conservation laws yielded a related set of differential equations. For obtaining the numerical solution of non linear problem, Runge Kutta technique is employed and listed in platform of MATLAB. The goal of this study is to illustrate the comprehensive analysis of repercussions of parameters on heat, velocity and nanoparticles concentration via graphical and numerical outcomes is computed. Both velocities (f1′ and f2) reduced against amplified value of β, λ and Fr but, have increasing behavior for α1 and α2. Heat distribution is rise with growing values of Fr and λ but, reduce in case of α1 (Prandtl fluid parameter) and α2 (elastic parameter) and concentration of nano particles is higher for λ and E but, lessen for δ. It is observed that the increment and decrement in values of f1′, f2, θ, ϕ by impact of variation in values of parameters is slightly fast in non aggregated phase as compared to aggregated phase. On linearly extending surface, Nu and friction factor variational patterns are numerically calculated.

Carbon quantum dots improve the mechanical behavior of polyvinyl alcohol/polyethylene glycol hydrogel

AbstractAs the wear and tear effects of artificial joints disturb patients after joint replacement, techniques of new lubrication materials or methods are constantly being investigated. Hydrothermal method was adopted to produce carbon quantum dots (CDs), and physically cross‐linked polyvinyl alcohol‐polyethylene glycol hydrogel (PVA‐PEG) to encapsulate CDs, which was evaluated as a lubricant for lubrication appraisal with their slow‐release solution. Results of the friction experiment showed that the addition of CDs changed the structure of the gel and promoted the tribological properties of the gel. The structural characterization results show that the CDs are successfully wrapped in gel. The network cross‐linked structure of the gel is improved due to the addition of CDs, which are shown by the results of thermogravimetric analysis (TGA) and differential scanning calorimetry analysis (DSC). At the same time, CDs can influence the thermal stability and crystallinity of the gel as well as the degree of cross‐linking. These results of TGA and DSC suggest that the curled molecular chain will not be stretched during the gel cross‐linking process. After 2 h of self‐healing, the recovered gel did not break again under the pull of external force. All these contribute to the preparation and application of hydrogels which is worth looking forward to accelerate the development of polymer lubrication.

Adjustable superlubricity system using polyalkylene glycol with various acid aqueous solutions

Polyalkylene glycol (PAG) aqueous solutions have recently been demonstrated to exhibit an ultralow friction coefficient (COF, μ < 0.01). However, the prolonged running-in period and low bearing capacity have limited its widespread application. In this study, we determined that the running-in period can be decreased by more than 75% when the pH value of the lubricant is controlled at 3 by introducing various acid solutions. Additionally, less time was required to realize stable superlubricity with inorganic acid at lower pH values. This was mainly attributed to the acceleration effect of hydrogen ions around the contact region. In case of PAG aqueous solution with organic acid, the wear loss between sliding solid surfaces was reduced, and thus the bearing pressure during the superlubricity period was significantly improved from approximately 30 to 160 MPa. Furthermore, the organic acid molecules were considered to form strong hydrogen bonds with PAG macromolecules and solid surfaces. This in turn strengthened the structure of the adsorption layers. The unique effect of different acids in aqueous polymer lubrication can potentially significantly aid in advancing the study of polymer tribology and broadening industrial applications.

Effectiveness of Radiation on Magneto-Combined Convective Boundary Layer Flow in Polar Nanofluid around a Spherical Shape

Many physical aspects emerging from the local structure and micromotions of liquid particles can be studied by utilizing the governing model of micropolar liquid. It has the ability to explain the behavior of a wide range of real fluids, including polymeric solutions, liquid crystals, lubricants, and animal blood. This earned it a major role in the treatment of many industrial and engineering applications. Radiative heat transmission induced by a combined convection flow of micropolar fluid over a solid sphere, and its enhancement via nanoparticle oxides, are investigated in this study. An applied magnetic field and a constant wall temperature are also considered. The Tiwari–Das model is used to construct the mathematical model. An approximate numerical solution is included using the Keller box method, in which its numerical calculations are performed via MATLAB software, to obtain numerical results and graphic outputs reflecting the effects of critical parameters on the physical quantities associated with heat transfer. The investigation results point out that a weakness in the intensity of the magnetic field, or an increment in the nanoparticle volume fraction, causes an increment in velocity. Raising the radiation parameter promotes energy transport, angular velocity, and velocity.

Machine Learning Approach for Application-Tailored Nanolubricants' Design.

The fascinating tribological phenomenon of carbon nanotubes (CNTs) observed at the nanoscale was confirmed in our numerous macroscale experiments. We designed and employed CNT-containing nanolubricants strictly for polymer lubrication. In this paper, we present the experiment characterising how the CNT structure determines its lubricity on various types of polymers. There is a complex correlation between the microscopic and spectral properties of CNTs and the tribological parameters of the resulting lubricants. This confirms indirectly that the nature of the tribological mechanisms driven by the variety of CNT–polymer interactions might be far more complex than ever described before. We propose plasmonic interactions as an extension for existing models describing the tribological roles of nanomaterials. In the absence of quantitative microscopic calculations of tribological parameters, phenomenological strategies must be employed. One of the most powerful emerging numerical methods is machine learning (ML). Here, we propose to use this technique, in combination with molecular and supramolecular recognition, to understand the morphology and macro-assembly processing strategies for the targeted design of superlubricants.

Exquisite Energy Savings at Cold Metal Forming of Threads through the Application of Polymers.

One of the global problems today is energy—its production and distribution. As the human population grows, the consumption of energy rises simultaneously. However, the natural sources are limited, and so the focus on power savings becomes more and more important. One of the ways to reduce consumption is the use of effective lubricants and tribological fluids in industry, especially in processes with high demands on energy but high quality of products as well. Forming is a typical example of such technology, and the application of polymers seems to be a very important challenge, because the application of straight oils or lubricant with extreme pressure additives seems to be prevailing in that field. Nevertheless, the polymer lubricant should fulfill all European standards as well as the environmental and ecological limitations with respect to health and the natural environment and its recycling and disposal. This paper is focused on the forming technology of threads and the application of selected polymers to the forming process. The measured and quantified criteria are torque and force loadings, energy consumption, and quality of the produced surfaces. Kistler dynamometers, scanning electron microscopy, and advanced surface topography with the use of Alicona IF-G5 were applied to assess all aspects of the tribological and energy aspects of six modern process fluids, three lubricating pastes, and two fluid modifications. The results show that the polymer synthetic lubricant (at volume concentration 20% in water) can reduce the total energy consumption by up to 40% per forming cycle (in mean values) at average surface roughness below 0.8 μm.

Aqueous lubrication and wear properties of nonionic bottle-brush polymers.

The usage of aqueous lubricants in eco-friendly bio-medical friction systems has attracted significant attention. Several bottle-brush polymers with generally ionic functional groups have been developed based on the structure of biological lubricant lubricin. However, hydrophilic nonionic brush polymers have attracted less attention, especially in terms of wear properties. We developed bottle-brush polymers (BP) using hydrophilic 2-hydroxyethyl methacrylate (HEMA), a highly biocompatible yet nonionic molecule. The lubrication properties of polymer films were analyzed in an aqueous state using a ball-on-disk, which revealed that BPHEMA showed a lower aqueous friction coefficient than linear poly(HEMA), even lower than hyaluronic acid (HA) and polyvinyl alcohol (PVA), which are widely used as lubricating polymers. Significantly, we discovered that the combination of HA, PVA, and BPHEMA is demonstrated to be essential in influencing the surface wear properties; the ratio of 1 : 2 (HA : BPHEMA) had the maximum wear resistance, despite a slight increase in the aqueous friction coefficient.

Improving the tribological performance of a biodegradable lubricant adding graphene nanoplatelets as additives

This research is based on the investigation of the tribological properties of a biodegradable polymeric ester lubricant (BIOE) additivated with two different pristine graphene nanoplatelets (GnPs), named as GnP7 and GnP40. These GnPs have lateral sizes of 7 and 40 μm, and thickness of 3 and 10 nm, respectively. Four different nanoadditive loadings: 0.015, 0.035, 0.055 and 0.075 wt% have been used. Stability of nanolubricants has been investigated using the visual control and the refractive index evolution during time, revealing a slightly better stability for the nanolubricants formulated with the largest lateral size graphene nanoplatelets (GnP40). The influence of the thickness and lateral size of these carbon-based nanoadditives on the antifriction and antiwear capabilities of BIOE is analysed. For this purpose, rotational friction tests were taken with the eight nanolubricants under a 20 N working load and 340 m sliding distance. All nanolubricants showed friction coefficients and worn area lower than those previously reported for the unadditivated BIOE. As regards friction, the ideal loading for both GnPs was 0.055 wt% GnP, being the best anti-friction behaviour obtained using GnP40 as additive (up to 26% reduction), whereas the 0.055 wt% GnP7/BIOE nanolubricant leads to the best anti-wear capability with wear reductions up to 56%. Finally, from Raman microscopy and roughness assessments on the worn surfaces, it can be determined that the good tribological performance of nanolubricants is owing to the protective film formation and surface repairing mechanism.

Finite element simulations of sliding contact of the head-disk interface in magnetic storage with lubricant effects

Perfluoropolyether (PFPE) polymer lubricant performs an important role in protecting both the writing/reading elements in the recording head and the disk of magnetic storage devices from mechanical wear or damage, induced by direct contact. Under high-speed sliding, the nanometer thick lubricant shows complex behavior, such as shear thinning, slippage and bonding ratio, making it difficult to directly test or simulate its performance. Based on a numerical model, the present study obtains the mechanical response of the lubricant under normal and sliding contacts. The mechanical response is then entered into a finite element model (FEM) through definition of material behavior of the lubricant using a hyper-elastic constitutive model. By comparing the sliding contact simulations with lubricant and without lubricant, it is found that the presence of lubricant helps to reduce the contact stresses, mainly because the contact area is increased.