The influencing mechanism of laser treatment on the tribological behavior of ultrahigh molecular weight polyethylene (UHMWPE) in a seawater environment was studied. The relation between the surface chemical composition and morphology of UHMWPE under different laser processing parameters and tribological properties in seawater environment was obtained. Oxidation and amorphization occurred when UHMWPE was lasertreated at relatively low-power densities (1.92 x 10(5) and 3.94 x 10(5) W/cm(2)), causing the slightly increase in wear rate of UHMWPE. Carbonization occurred after relatively high-power densities laser treatment (6.01 x 10(5), 8.12 x 10(5) and 1.00 x 10(6) W/cm(2)), causing significantly increase in wear resistance and decrease in friction coefficient. The laser-induced carbonization products were mainly composed of amorphous and graphitic carbon, which served as a solid lubricant during friction, thereby significantly improving the tribological properties of UHMWPE in the seawater environment. A method of laser-induced carbonization was proposed to improve the tribological properties of polymer materials in a seawater environment. Controlling the degrees of surface oxidation and carbonization of UHMWPE effectively regulated its tribological properties in seawater environments.

Friction and wear are ubiquitous, from nano-electro-mechanical systems in biomedicine to large-scale integrated electric propulsion in aircraft carriers. Applications of nanomaterials as lubricating oil additives have achieved great advances, which are of great significance to control friction and wear. This review focuses on the applications of nanomaterials in lubricating oil and comprehensively compares their tribological characteristics as lubricating oil additives. Statistical analysis of tribology data is provided and discussed accordingly; moreover, the interaction between nanomaterials and sliding surface, lubricating oil, other additives, and synergistic lubrication in nanocomposites are systematically elaborated. Finally, suggestions for future research on nanomaterials as lubricating oil additives are proposed. Hence, this review will promote a better fundamental understanding of nanomaterials for lubricating oil application and help to achieve the superior design of nanoadditives with outstanding tribological performances.

In this work, blended composites with ultra-high molecular weight polyethylene (UHMWPE) as matrix polymer, alpha-zirconium phosphate (alpha-ZrP) as filler, and sodium polyacrylate (PAANa) as compatibilizer were prepared. The interfacial interaction between PAANa as a compatibilizer and the components of alpha-ZrP/UHMWPE was studied by molecular dynamics simulation. The friction and wear behavior of the GCr15 ball/composite friction pair under seawater lubrication under different loads were explored, and the friction and wear mechanism were analyzed. The results show that PAANa as a compatibilizer can effectively improve the interfacial interaction force between components of PAANa/alpha-ZrP/UHMWPE composites. The composites exhibited different trends regarding the relationship between tribological properties and alpha-ZrP content under various loads. The wear mechanism of composites under low load is mainly represented by extrusion deformation. With the increase of load, the wear mechanism of composites gradually changed into adhesive wear and abrasive wear (depending on the content of alpha-ZrP). This work provides a theoretical basis for preparing and applying other alpha-ZrP/polymer blend composites.

Herein, the tribological behavior of multi-walled carbon nanotube (MWCNT)/polyimide (PI) composites in water was investigated based on manufacturing optimization using response surface methodology (RSM). Wear surfaces and transfer films were analyzed by SEM, EDS, TEM, and Raman spectroscopy. It indicates that the molding process for neat PI and MWCNT/PI is deeply subjected to a narrow processing temperature window. Depending on the positive drift of the glass transition temperature for MWCNT/PI, the tribological properties in water were significantly affected by molding temperature. Besides, combined with experimental results and simulation analysis, it suggested that MWCNT performs rolling and/or sliding motions in molecular bearings form between frictional pairs for enhanced lubrication.

Polymer materials are widely used in the mechanical lubricant field owing to their light, low-cost, anti-corrosion, and excellent self-lubricating performance. Adding functional fillers with anti friction and reinforcing character can overcome the inherent defects of intrinsic polymer materials and then obtaining tribological composites materials with the low friction coefficient, high-wearing, high bearing, and heat-resisting performance. The anti-friction and anti-wear effect and mechanism of composites by adding functional fillers such as carbon-based materials, transition metal sulfides, microcapsules, soft metals, ceramic nanoparticles, mineral salts, and self-lubricant polymer materials were summarized in this paper. Meanwhile, the mechanical property is the key parameter that can guarantee the service performance and application deadline of polymer materials and also gives the significant influence of tribological performance. The enhanced and toughening mechanism of composites by adding nanoparticles and fiber was also mainly discussed in this paper. Finally, The synergistic effect of functional fillers on mechanical and tribological properties was prospected, as well as the development trend of computer simulation in tribology of composite materials.

Abstract Ultrahigh molecular weight polyethylene (UHMWPE) has been extensively used in various tribological systems because of its outstanding tribological properties and excellent overall performance. Compression molding is the main molding method for UHMWPE, and the process parameters of molding have a profound effect on its material properties. In this study, three groups of UHMWPE samples were prepared, and their physical, mechanical, and tribological properties under different molding process parameters were examined—with a particular focus on the frictional and wear behavior of the material under various heating-temperatures, pressing-temperatures and pressures—and the friction and wear mechanisms of UHMWPE were analysed. Studies have shown that the rise in heating-temperature promotes the diffusion of polymer chains, resulting in an increased friction coefficient and wear loss of UHMWPE. The main wear mechanism switches from plastic deformation to fatigue wear. With an increase in the pressuring-temperature, the friction coefficient first increases and then decreases, while the wear loss increases, and the dominant wear mechanism switches from fatigue wear and plastic flow to plastic flow. With an increase in pressure, the friction coefficient and wear loss first decrease and then increase, and the prime wear mechanism changes from plastic deformation and fatigue wear to fatigue wear.

Polymers are widely used in wading sports equipment because of their excellent friction reducing and wear-resisting properties. In wading sports equipment, electromagnetic control is often used to manipulate the switch and operation of underwater equipment, so that the moving friction pair and the wear debris generated by friction will change under the action of magnetic field. We studied the effects of particles and magnetic field strength on the friction and wear properties of ultra-high molecular weight polyethylene (UHMWPE) nylon 66 (PA66) material in solution environments. The main conclusions of this paper are as follows: The application of magnetic field can improve the friction reducing properties of UHMWPE and PA66, but the wear resistance of PA66 is not significantly raised. In seawater, adding powder while applying magnetic field makes the friction reduction and wear resistance of UHMWPE and PA66 better, while adding powder in pure water makes the friction reduction of UHMWPE and PA66 worse, and wear resistance better. The magnetic field can affect the friction and wear mechanism by affecting the size of the abrasive particles in the friction pair. After adding the particles, the abrasive particles are refined under the influence of the magnetic field, and the particles adhere to the wear surface, reducing the corrosion current density of the system, thereby improving the friction of the material and the corrosion performance of the solution.

Exposing engineering plastics to UV irradiation can easily destroy the original molecular structure of the materials and consequently affect their tribological properties. This study investigated the effects of UV irradiation on the molecular structure of typical engineering plastics, such as polytetrafluoroethylene (PTFE) and polyether ether ketone (PEEK), and on their tribological properties under heavy loads (20 MPa). The surface morphology results showed that the appearance of PEEK changed significantly under UV irradiation. However, the change in PTFE was negligible. Under micromorphology, the processing lines of the two materials gradually became lighter with increasing UV irradiation time. The resulting infrared spectra showed that the molecular chains of both materials were broken, and new functional groups were formed under UV irradiation. Tribology testing demonstrated that with prolonged UV irradiation, the average PTFE coefficient of friction remained relatively stable, whereas that of PEEK was approximately 0.55. As the UV irradiation time increased, the wear rate of PTFE increased significantly, whereas that of PEEK showed no significant change.

The effect of laser treatment on the tribological performance of PEEK under seawater lubrication was studied. The surface morphology and wettability of the laser treated PEEK were analyzed. The relationship between the surface chemical composition and the tribological performance of the laser treated PEEK was discussed. Results show that oxidation occurred during laser treatment with relatively low laser power density, there was no obvious change in surface roughness. Carbonization occurred for the treatment with high laser power density, surface roughness increased significantly, made the surface more hydrophobic. The friction of PEEK under artificial seawater lubrication was reduced after laser treatment. The reduction in friction for the laser treated PEEK under low power density was mainly due to the adsorption of water molecules and cations on the surface of PEEK. For the PEEK treated with high laser power density, solid lubrication due to surface carbonization was the main reason for the reduction of friction and wear.

Shock waves and micro-jets generated during the process of bubble collapse lead to cavitation damage on the surface of materials in hydraulic machinery equipment parts, which is attention. However, research on the dynamics of bubble collapse is still unclear. In this work, molecular dynamics (MD) simulations are used to study the compression and collapse processes of microscopic bubbles under the impact of different velocities for water molecules. The velocities of the shock wave, time of bubble collapse and shock pressure of collapse were obtained. Results showed that higher the impact velocity, shorter is the time of bubble collapse and the higher velocity of the micro-jet. After the bubble collapse, the micro-jet will form secondary water hammer shocks and a greater shock pressure. The water structure appears to undergo a phase change (ice-VII structure) when the velocity of water molecules is 1.0 km s(-1). The shock induces the bubble collapse and the micro-jet significantly increases the chemical activity of water molecules; the degree of ionization of water molecules increases with the shock velocity. In addition, the Hugoniot curve of the shock velocity obtained by molecular dynamics simulations are in good agreement with the experimental data.

Biofilms are aggregates of bacterial cells surrounded by an extracellular matrix. Much progress has been made in studying biofilm growth on solid substrates; however, little is known about the biophysical mechanisms underlying biofilm development in three-dimensional confined environments in which the biofilm-dwelling cells must push against and even damage the surrounding environment to proliferate. Here, combining single-cell imaging, mutagenesis, and rheological measurement, we reveal the key morphogenesis steps of Vibrio cholerae biofilms embedded in hydrogels as they grow by four orders of magnitude from their initial size. We show that the morphodynamics and cell ordering in embedded biofilms are fundamentally different from those of biofilms on flat surfaces. Treating embedded biofilms as inclusions growing in an elastic medium, we quantitatively show that the stiffness contrast between the biofilm and its environment determines biofilm morphology and internal architecture, selecting between spherical biofilms with no cell ordering and oblate ellipsoidal biofilms with high cell ordering. When embedded in stiff gels, cells self-organize into a bipolar structure that resembles the molecular ordering in nematic liquid crystal droplets. In vitro biomechanical analysis shows that cell ordering arises from stress transmission across the biofilm-environment interface, mediated by specific matrix components. Our imaging technique and theoretical approach are generalizable to other biofilmforming species and potentially to biofilms embedded in mucus or host tissues as during infection. Our results open an avenue to understand how confined cell communities grow by means of a compromise between their inherent developmental program and the mechanical constraints imposed by the environment.

Engineering plastics are macromolecular compounds composed of covalently bonded macromolecules, which have been widely used in sliding wear-resistance materials in isolation bearings. In this study, an MFT-5000 reciprocating friction testing machine was used to compare the friction and wear performance of polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), and ultra-high molecular weight polyethylene (UHMWPE) under heavy load conditions in dry friction condition. The results show that load has a significant effect on the friction coefficient, wear rate, and wear mechanism of three materials. The instant friction coefficient of PTFE fluctuates under high load, the wear rate clearly increases with the increase in load. Therefore, the application under high load conditions is limited. The wear rate of UHMWPE is the least affected by the load among the three materials. Even when the load exceeds the yield strength, the wear resistance is still good. The friction coefficient of PEEK decreases with the increase in load but maintains a high value that restricts its application in sliding friction pair materials to some degree.

Determining the nature of the microscopic mechanism of tribological properties by experimental methods for a polymer material surface/interface in the sliding friction process is a challenge. Molecular dynamics simulations were conducted by sliding a rigid indenter over the amorphous polyethylene. The results show that the friction is mainly composed of plough force and adhesion force. The average friction of adhesive contact is greater than that of frictionless contact because of the adhesion effect. The difference of average friction between adhesive contact and frictionless contact increases with increasing indentation depth because of the plough force effect. The elastic deformation of amorphous polyethylene in the cohesive zone is related to van der Waals interaction energy, whereas the plastic deformation was mainly dominated by bond angle energy and dihedral energy of the molecular chain for amorphous polyethylene. Molecular chains of amorphous polyethylene extend along the sliding direction and agglomerate along the indentation direction. The flexibility of the molecular chains increases with the increase of temperature and facilitates the molecular chains returning more easily to their original state.

Ni-Co/WC composite coating was fabricated on ZG45 steel substrate through vacuum sintering cladding technology. Its microstructure, composition, and three-point bending behavior were analyzed through scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and mechanical testing. Results show that the distribution of WC particles presents a 3D net-like shape. A metallurgical fusion area is observed at the interface between the composite coating and the substrate. The entire coating consists of a composite coating area, a transition area, and a diffusion fusion area. The main phases of the coating are WC, Cr7C3, Cr23C6, Ni3Si, FeNi3, and Ni-Co solid solution. Three-point bending results reveal that the softness coefficient of the whole sample when the composite coating was in a compressive stress state was larger than that when the composite coating was in a tensile stress state. The bending strength of the sample is 520 MPa when the composite coating is in a compressive stress state. This value is 66% higher than that when the composite coating is located at the bottom. The cracks simultaneously extend to the substrate and interface when the composite coating was in a compressive stress state and to the substrate when the composite coating was in a tensile stress state. The fracture of the composite area is brittle, and the substrate fracture is ductile.

Molecular models were established to predict the miscibility of polyimide/polythene mixing systems and the enhancing effects of compatibilizer addition of maleic anhydride grafted polythene (MAH-g-PE). Molecular dynamics simulations were applied to investigate radial distribution functions and Flory-Huggins parameters of the mixing systems. Results show that polyimide/polythene is miscible to a certain degree, and the miscibility gets better after adding MAH-g-PE. Dissipative particle dynamics (DPD) simulations display that microphase separation occurs in the polyimide/polythene mixing systems, however, effective interfaces appear between polyimide and polythene phases after adding MAH-g-PE. The results of molecular mechanics simulations indicate that the ability of mixing systems to resist stretch, compression and shear deformation increases after adding MAH-g-PE. This work offers a promising technique to predict miscibility properties for polyimide/polythene system prior to actual production and attempt to find a suitable compatibilizer for that system.

Polyimide-modified ultrahigh molecular weight polyethylene (UHMWPE) composites were fabricated by hot-press molding process. Mesoscopic morphologies of polyimide/UHMWPE blending systems show high compatibility between the phases of polyimide and UHMWPE when the weight ratio of polyimide is no more than 50wt%. Investigation of the tribological properties with a reciprocating ball-on-flat contact tribometer shows that the polyimide filler has important effects on the friction and wear behavior of UHMWPE composites. Compared to pure UHMWPE, the composite with 50wt% polyimide improved tribological properties best and exhibited 43.1% reduction in friction coefficient and 66.7% reduction in wear volume loss. [GRAPHICS] .

Biofilms are collections of microorganisms that aggregate using a self-produced matrix of extracellular polymeric substance. It has been broadly demonstrated that many microbial infections in the body, including dental plaque, involve biofilms. While studying experimental models of biofilms relevant to mechanical removal of oral biofilms, distinct ripple patterns have been observed. In this work, we describe a multiphase model used to approximate the dynamics of the biofilm removal process. We show that the fully nonlinear model provides a better representation of the experimental data than the linear stability analysis. In particular, we show that the full model more accurately reflects the relationship between the apparent wavelength and the external forcing velocities, especially at mid-to-low velocities at which the linear theory neglects important interactions. Finally, the model provides a framework by which the removal process (presumably governed by highly nonlinear behavior) can be studied.

High concentration hydrogen peroxide solutions (HCHP) have been attractive as potentially future fuels. However, preparing inner moving-parts with both good compatibility and tribological properties under HCHP remains to be a challenge. Here, the high entropy alloys (HEAs)/Si3N4 tribol-pair with compatible alloy and self-lubricating counterpart was researched. The wear-mechanisms and alloy-structure effects were studied. As a result, the realization of lubricated friction depends on whether the condition meet Vformtion (formation velocity of colloidal films)-Vattrition (attrition velocity of colloidal films)>Vpit (increase velocity of pit depth and amount). HEAs with poorer corrosion resistance and higher strength could more easily achieve effective lubrication. The component inhomogeneity of different structures could promote the corrosion behavior.

In this work, the effects of Single-walled carbon nanotubes (SWNTs), 4-Chloro-3, 5-Dimethylphenol (PCMX) adsorbed SWNTs (named SWNTs-PCMX) and Poly-hexamethylene Biguanide Hydrochloride (PHMB) adsorbed SWNTs (named SWNTs-PHMB) on growth of Escherichia coli (E. coli) were investigated. The results showed that low concentration (0.1g/L) of SWNTs had no significant effect on the growth of E. coli, while 1g/L SWNTs inhibited E. coli. Within 25min, the killing log (KL) of SWNTs-PCMX (450mg/L) was 8.66 folds of KL without PCMX, in contrast the bactericidal activity was still lower than PCMX. The results of Fourier Transform Infrared Spectroscopy (FTIR) showed that the functional groups of PCMX in SWNTs-PCMX were adsorbed into the cavity of SWNTs, which led to the decrease of bactericidal effect. However, with the increase of time, the bactericidal activity of SWNTs-PCMX was enhanced, and it had a slow release effect. To further improve the bactericidal effect of SWNTs, the PCMX was replaced by PHMB, the KL of SWNTs-PHMB (320mg/L) was 2.7 folds than that of SWNTs-PCMX (450mg/L).