Lubricant Layer Research Articles

Nonlinear Stochastic Modeling with Heterogeneous Covariates for Degradation Analysis Applied to Wax Lubrication Layer

Wax is a commonly used lubricant in many applications. To ensure its security and dependability, degradation analyses for creep are typically conducted. However, challenges arise due to the poorly understood inherent mechanisms of wax and the complicated experimental environment required, leading to nonlinear trends and heterogeneous covariates. In such cases, traditional methods based on parametric forms or linear assumptions may lack the flexibility to capture the complexities and randomness of the degradation process effectively. To address these challenges, we propose a comprehensive degradation analysis framework that employs a Wiener process with an unspecified mean function. By eliminating parametric forms, this approach offers a more versatile way to model nonlinear degradation trends. Moreover, it treats environmental covariates as random variables to handle random environmental influences. We develop tailored semiparametric estimators for the model and establish theoretical asymptotic results that guarantee the consistency and convergence of the proposed estimators. A series of numerical experiments are conducted to illustrate the performance of the estimators and validate their convergence properties. The method is applied to a wax lubrication layer, demonstrating its efficacy in analyzing nonlinear degradation data in a random working environment. This work advances the understanding of wax degradation mechanisms and provides a flexible tool for degradation analysis in materials with heterogenic environments and poorly understood behaviors.

Surface cleaning with atmospheric pressure plasma jet investigated by in-situ optical emission spectroscopy and laser-induced breakdown spectroscopy

Cleaning of surfaces with atmospheric pressure plasma jet (APPJ) is investigated by in-situ optical emission spectroscopy (OES) and laser-induced breakdown spectroscopy (LIBS). The APPJ device operates a spark discharge of kW power in Argon gas flow resulting in a powerful plasma jet expanding into air. For cleaning experiments samples are coated with lubricant layers of 1.1 to 7.1 µm thickness. Light collected at the sample surface during APPJ treatment is analyzed spectroscopically and used to monitor the cleaning process. LIBS chemical imaging delivers spatial cleaning profiles of plasma treated surfaces. From measured emission intensities of CN molecular band and Na atomic line the cleaning efficiencies for carbon and Na containing contaminants are determined. The power of APPJ plasma generator, distance between sample and jet nozzle, scan speed, and Argon gas flow are varied to optimize the surface treatment. Thermal and non-thermal processes contribute to cleaning. For the carbon containing contaminant thermal processes are dominating (∼90 %) while also non-thermal processes (∼30–45 %) are relevant for the Na containing component. A cleaned surface area per time from 0.3 to 10 cm2/s is investigated. Cleaning efficiency up to 95 % is obtained highlighting the potential of APPJ surface cleaning under ambient conditions.

Continuous Hyaluronic Acid Supply by a UHMWPE/PEEK Interlocking Scaffold for Metatarsophalangeal Joint Prosthesis Lubricating Applications.

Wear is one of the main causes of prothesis failure in hemiarthroplasty of small joints such as the metatarsophalangeal joint, to which lubrication improvement is a promising solution. Inspired by the natural joint structure and lubrication mechanisms, we developed a novel composite strategy for metatarsophalangeal joint hemiarthroplasty. An ultrahigh-molecular-weight polyethylene (UHMWPE) lubrication layer is interlocked within a 3D-printed poly(ether ether ketone) (PEEK) scaffold, and hyaluronic acid (HA) is introduced for hydrophilic modification of the UHMWPE matrix. HA encapsulated in the matrix can consistently emerge to the friction interface and firmly form a boundary lubrication layer, consequently enhancing the lubrication of the UHMWPE component. The friction coefficient of the scaffolds could be as low as 0.041 under a joint-equivalent load and a low friction velocity. Besides, the tested samples demonstrate good in vitro and in vivo biocompatibility. The bone tissues around the implantation site can heal normally and achieve implant fixation within 6 weeks. Summarily, in this work, inspired by the natural "cartilage-and-subchondral bone" structure, a continuous HA supply was attained in a UHMWPE/PEEK interlocking scaffold. Such a composite shall provide an excellent combination of tribological properties and biocompatibility, thus hopefully being a candidate material for the next-generation hemi-implants for metatarsophalangeal arthroplasty.

Analytical solution for the hydrodynamic resistance of a disk in a compressible fluid layer with odd viscosity on a rigid substrate.

Chiral active fluids can exhibit odd viscosity, a property that breaks the time-reversal and parity symmetries. Here, we examine the hydrodynamic flows of a rigid disk moving in a compressible 2D fluid layer with odd viscosity, supported by a thin lubrication layer of a conventional fluid. Using the 2D Green's function in Fourier space, we derive an exact analytical solution for the flow around a disk of arbitrary size, as well as its resistance matrix. The resulting resistance coefficients break the Onsager reciprocity, but satisfy the Onsager-Casimir reciprocity to any order in odd viscosity.

Anti-icing properties of nonionic/hydrophilic concentrated polymer brushes and mechanistic insights via their swollen-state analysis

Anti-icing surfaces are important to prevent snow and ice accumulation, which can pose significant risks. Here, we analyze the anti-icing performance of concentrated polymer brushes (CPBs) consisting of a versatile nonionic/hydrophilic monomer and discuss the low-temperature properties of the CPB-retaining water. The anti-icing functionality is evaluated by measuring the ice adhesion strength as a function of the temperature and the structural parameters (e.g., density and length) of the polymer brushes. We demonstrate that only the CPB region (σ* ≥ 0.15) exhibits both high anti-icing functionality and excellent durability. Furthermore, the thickening of the CPBs is key to achieving a detailed characterization of the water present in the CPBs at low temperatures using in situ microscopic Fourier-transform infrared spectroscopy and differential scanning calorimetry. These results suggest that the water effectively remaining via quasi-equilibrium partial deswelling formed a lubricating layer, contributing to high anti-icing functionality and durability.

Fracturing behaviour of a shear-thinning fluid in a lubricated Hele-Shaw cell

We undertake an experimental investigation into the instabilities that emerge when a shear-thinning fluid intrudes a less viscous Newtonian fluid axisymmetrically in a lubricated Hele-Shaw cell. Pre-formed lubrication layers of Newtonian fluid that separate the shear-thinning fluid from the cell walls are incorporated into the experimental design. Provided the lubrication layers remain effective at reducing shear stress, so that extensional stresses dominate the flow of the intruding fluid, the instabilities evolve to form branch-like structures, which exhibit fracturing or tearing behaviour at their troughs. Thicker lubrication layers enable the branches to propagate radially outwards, whilst thinner, less effective ones hinder their development and progression. In the absence of lubrication layers, the shear-thinning fluid spreads radially and remains axisymmetric. For lubricated flows, we show that the number of branches is dependent primarily on the strain rate at the radial distance where they first emerge, and that the number of branches decreases with increasing strain rate.

Earthworm inspired lubricant self-pumping hydrogel with sustained lubricity at high loading

The development of mechanically robust super-lubrication hydrogel materials with sustained lubricity at high contact pressures is challenging. In this work, inspired by the durable lubricity feature of the earthworm epidermis, a multilevel structural super-lubrication hydrogel (MS-SLH) system, the so-called lubricant self-pumping hydrogel, is developed. The MS-SLH system is manufactured by chemically dissociating a double network hydrogel to generate robust and wrinkled lubrication layer, and then laser etching was used to generate cylindrical texture pores as gland-like pockets for storing lubricants. The surface of MS-SLH system shows ultrafast hydration characteristics and reversible pore-closing and pore-opening behavior. The current MS-SLH system shows excellent SL features, as follows: a very low COF (~0.0079) at high contact pressure condition (P: 11.32 MPa); a stable and robust SL lifespan (COF: ~0.0028, P: 8.48 MPa, 100k cylces) without surface wear; and a sustained lubricity period (3700 cycles) with limited lubricant volume (5 μL) in air. The robust and sustained lubricity of the MS-SLH system is likely attributed to the synergy from the strong electrostatic repulsion effect at the sliding interface, the robust but compliant modulus of the dissociation lubrication layer, and the self-pumping lubricant release from the gland-like pocket of the texture pores during the dynamic shearing process. The demonstration experiments based on self-built equipments intuitively exhibit durable SL behavior of MS-SLH system. This work provides an easy strategy for the large-scale manufacture of high-performance water-lubrication coatings suitable for high-end medical devices or moving parts.

Advances in small droplets manipulation on bio-inspired slippery surfaces: chances and challenges.

The manipulation of droplets with non-destructive, efficient, and high-precision features is of great importance in several fields, including microfluidics and biomedicine. The lubrication layer of bioinspired slippery surfaces demonstrates remarkable stability and self-restoration capabilities when subjected to external perturbations. Consequently, research into the manipulation of droplets on slippery surfaces has continued to make progress. This paper presents a review of the methods of droplet manipulation on bioinspired slippery surfaces. It begins by outlining the basic theory of slippery surfaces and the mechanism of droplet motion on slippery surfaces. Furthermore, droplet manipulation methods on slippery surfaces are classified into active and passive approaches based on the presence of external stimuli (e.g., heat, light, electricity, and magnetism). Finally, an outlook is provided on the current challenges facing droplet manipulation on slippery surfaces, and potential solution ideas are presented.

Robust, Scalable Microfluidic Manufacturing of RNA-Lipid Nanoparticles Using Immobilized Antifouling Lubricant Coating.

Despite the numerous advantages demonstrated by microfluidic mixing for RNA-loaded lipid nanoparticle (RNA-LNP) production over bulk methods, such as precise size control, homogeneous distributions, higher encapsulation efficiencies, and improved reproducibility, their translation from research to commercial manufacturing remains elusive. A persistent challenge hindering the adoption of microfluidics for LNP production is the fouling of device surfaces during prolonged operation, which significantly diminishes performance and reliability. The complexity of LNP constituents, including lipids, cholesterol, RNA, and solvent mixtures, makes it difficult to find a single coating that can prevent fouling. To address this challenge, we propose using an immobilized liquid lubricant layer of perfluorodecalin (PFD) to create an antifouling surface that can repel the multiple LNP constituents. We apply this technology to a staggered herringbone microfluidic (SHM) mixing chip and achieve >3 h of stable operation, a >15× increase relative to gold standard approaches. We also demonstrate the compatibility of this approach with a parallelized microfluidic platform that incorporates 256 SHM mixers, with which we demonstrate scale up, stable production at L/h production rates suitable for commercial scale applications. We verify that the LNPs produced on our chip match both the physiochemical properties and performance for both in vitro and in vivo mRNA delivery as those made on chips without the coating. By suppressing surface fouling with an immobilized liquid lubricant layer, this technology not only enhances RNA-LNP production but also promises to transform the microfluidic manufacturing of diverse materials, ensuring more reliable and robust processes.

SURFACE INVESTIGATION OF HIGH TEMPERATURE WEAR BEHAVIOR OF SS316L ALLOY PRODUCED BY LASER POWDER BED FUSION

This research investigates the tribological characteristics of SS316L produced through Laser Powder Bed Fusion (LPBF), emphasizing the influence of testing temperature, sliding velocity, and loading conditions. The findings demonstrate that the friction coefficient escalates with increased temperatures (150°C and 250°C), whereas the wear rate remains invariant, presumably attributable to the establishment of a lubricating surface layer. The rotational velocity of 300 revolutions per minute the Coefficient of Friction (COF) shown an upward movement although the wear rate remains constant. The findings underscore the importance of analyzing different parameters to understand the friction and wear properties of additively manufactured SS316L.

A comparative analysis of different surface tribological and electrochemical properties of TiAlN, TiAlSiN, and CrAlN thin film coatings in seawater

Abstract To reveal the wear mechanisms of TiAlN, TiAlSiN, and CrAlN coatings in a seawater environment, the changes in frictional surfaces and the electrochemical characteristics of these coatings were compared and analyzed in this paper. The coatings were deposited on 316L stainless steel surfaces. Tribological tests were investigated using a ball-on-disk tribometer with Si3N4 ceramic balls as the counter material. Although the friction coefficient of 316L stainless steel was the lowest at 0.34, the order of wear rates was 316L stainless steel (7.38×10-5)>TiAlN(5.31×10-6)>TiAlSiN(4.23×10-6)>CrAlN(1.10×10-6) and the electrochemical protective efficiencies of TiAlSiN and CrAlN were both greater than 97%. Seawater penetrated through the grain boundaries of the TiAlN coating, which led to corrosion and delamination failure. Conversely, the grain refinement in TiAlSiN and CrAlN coatings can significantly slow down the penetration of seawater into the coating under frictional pressure, and the oxide lubricating layer formed during the friction process can become an effective barrier to isolate seawater. Therefore, mechanical wear was the main wear form of these two coatings. Additionally, among the oxides formed in the friction, Cr2O3 showed the strongest corrosion resistance, making the CrAlN coating exhibit superior wear resistance and the lowest wear rate in seawater.

Lubrication-mediated rebounds off fluid baths

We present herein the derivation of a lubrication-mediated (LM) quasi-potential model for droplet rebounds off deep liquid baths, assuming the presence of a persistent dynamic air layer which acts as a lubricating pressure transfer. We then present numerical simulations of the LM model for axisymmetric rebounds of solid spheres and compare quantitatively to current results in the literature, including experimental data in the low-speed impact regime. In this regime the LM model has the advantage of being far more computationally tractable than direct numerical simulation (DNS) and is also able to provide detailed behaviour within the micro-metric thin lubrication region. The LM system has an interesting mathematical structure, with the lubrication layer providing a free-boundary elliptic problem mediating the drop and bath free-boundary evolutionary equations.

Effects of urea-functionalized MoS2 on hydrophilic lubrication

Effects of urea-functionalized MoS2 on hydrophilic lubrication

Fabrication of reusable SERS substrate based on pillar-assisted organogel

Fabrication of reusable SERS substrate based on pillar-assisted organogel

Multiresponsive Ionogel with Switchable Adhesion Triggered by Phase Separation.

The rapid development of wearable devices and soft robotics has an urgent demand for polymer conductors with a switchable adhesion property. Herein, we report a supramolecular ionogel (SIG) that can reversibly switch between adhesion and debonding to various substrates. The on/off switchable adhesion of SIG is attributed to phase separation induced by the aggregation of polymer chains and the formation of a lubricating layer, which impairs the contact between polymer chains and substrates, thus weakening interfacial interaction. The phase separation ionogel (PSIG) is highly sensitive to humidity, leading to the debonded PSIG instantly transforming into the adhesion-hydrated ionogel (HIG) owing to the disruption of phase structure. Based on the switchable adhesion property, this multiresponsive ionogel shows potential applications as a fire alarm and intelligent conductive tape. This work provides a simple method for developing a switchable adhesion ionic polymer conductor and broadens the application of the ionogel in flexible devices.

Immunoregulative coating for scarless healing in anterior cruciate ligament reconstruction

Immunoregulative coating for scarless healing in anterior cruciate ligament reconstruction

Investigation of MoSe2 filled MAO Coating on TC6 alloy- tribological and corrosion characterization of multiple interface structure

Investigation of MoSe2 filled MAO Coating on TC6 alloy- tribological and corrosion characterization of multiple interface structure

Comparative study on the performance of fresh concrete comprising manufactured sand vs. river sand during full-scale long-distance pumping

Comparative study on the performance of fresh concrete comprising manufactured sand vs. river sand during full-scale long-distance pumping

Inertial Ferrofluidic Sensor for Vibration, Displacement and Impulse Measurement with a Linear Output Signal

The aim of the work is to develop the uniaxial ferrofluid sensor suitable for use either as an accelerometer for low-frequency vibrations or as a ballistic device or seismic sensor for shock loads. The goal is achieved by solving the following problems: development of a magnetic suspension system with a linear axial gradient of the magnetic field strength, calculation of the viscous friction force of the magnetic fluid filling the coaxial layer between the magnetic cylinder and the non-magnetic body wall, manufacturing of the sensor and its static and dynamic tests. The most significant result of the work is the experimental confirmation of the linearity of the electromechanical system of the sensor, corresponding to the model representations of a linear dissipative oscillating system with one degree of freedom. The significance of the obtained results lies in the appearance of cheap and simple linear inertial sensors. The principle of operation of the sensor is based on the registration of the motion of an inert mass deviating from the equilibrium position under the action of an external force to be measured. The inert mass, consisting of ring permanent magnets, levitates in a coaxial layer of magneto-fluid lubricant. The sensor, depending on its parameters, can measure either quasi-static force, or force impulse, or coordinate displacement, which is in demand in monitoring systems for critical structures and buildings, as well as in navigation systems for vehicles operating under conditions of small, slowly changing accelerations (microgravity).

A bio-inspired Janus hydrogel patch facilitates oral ulcer repair by combining prolonged wet adhesion and lubrication

A bio-inspired Janus hydrogel patch facilitates oral ulcer repair by combining prolonged wet adhesion and lubrication