Friction properties of polyacrylamide hydrogel particle/HDPE composite under water lubrication

Synergistic Effect of Microconvex Texture and Particle Medium on the Tribological Property of the Rubber Sliding Interface

In this study, we examined how surface topography and particle medium interact to affect the tribological performance of rubber sliding interfaces, uncovering the mechanisms of particle lubrication under various conditions. We found that microtextured surfaces, created using a mold transfer method, modestly reduced the friction coefficient of rubber under both dry and lubricated states, primarily by altering the real contact area. Additionally, the presence of different microconvex textures on the surface topography significantly influenced rubber's tribological properties. Our three-dimensional morphological analysis revealed that microtextured rubber surfaces with higher Sa, Sku, and Sal and lower Str values consistently showed lower friction coefficients during sliding. The friction mechanism was attributed to the combined effects of the material properties, surface topography, and contact area. With the addition of a particle medium, the dry friction coefficient of the rubber interface decreased but exhibited an initial increase, followed by a decrease with increasing particle diameter. When particles were mixed with a water-based cutting fluid, the concentration, diameter, and wettability of the particles significantly impacted the tribological properties due to the synergistic effects of surface topography and particle lubrication. This work enhances our understanding of tribological control for viscoelastic materials through surface design, providing a theoretical basis for the tribological optimization of rubber surfaces.

Tribological Behavior of Cotton Fabric/Phenolic Resin Laminated Composites Reinforced with Two-Dimensional Materials

In this study, cotton fabric-reinforced phenolic resin (CPF) composites were modified by adding four two-dimensional fillers: graphitic carbon nitride (g-C3N4), graphite (Gr), molybdenum disulfide (MoS2), and hexagonal boron nitride (h-BN). The tribological properties of these modified materials were investigated under dry friction and water lubrication conditions. The CPF/Gr composite exhibits significantly better tribological performance than the other three filler-modified CPF composites under dry friction, with a 24% reduction in friction coefficient and a 78% reduction in wear rate compared to the unmodified CPF composite. Under water lubrication conditions, all four fillers did not significantly alter the friction coefficient of the CPF composites. However, except for an excessive amount of Gr, the other three fillers can reduce the wear rate. Particularly in the case of 10% MoS2 content, the wear rate decreased by 56%. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed for the analysis of the morphology and composition of the transfer films. Additionally, molecular dynamics (MD) simulations were conducted to investigate the adsorption effects of CPF/Gr and CPF/MoS2 composites on the counterpart surface under both dry friction and water lubrication conditions. The difference in the adsorption capacity of CPF/Gr and CPF/MoS2 composites on the counterpart, as well as the resulting formation of transfer films, accounts for the variation in tribological behavior between CPF/Gr and CPF/MoS2 composites. By combining the lubrication properties of MoS2 and Gr under dry friction and water lubrication conditions and using them as co-fillers, we can achieve a synergistic lubrication effect.

Cartilage-bioinspired, tough and lubricated hydrogel based on nanocomposite enhancement effect

The maintenance of high load-bearing tissues and joint lubrication is essential for suppressing osteoarthritis. The lubrication of natural joints is mainly attributed to the hydration lubrication mechanism of articular cartilage. Phospholipids on the cartilage surface attract water molecules to form a tough hydrated layer to reduce friction. In this work, inspired by the phosphatidylcholine lipids, we synthesized lubricated nanospheres by grafting hydrophilic polymer brushes and further synthesized a nanocomposite hydrogel. The addition of the lubricated nanospheres enhanced both the mechanical and lubricated properties of the hydrogel. The nanocomposite-lubricated hydrogel exhibited a friction coefficient 81.7% lower than the blank hydrogel because of grafting the polymer brushes. Also, the nanocomposite enhancement helped the hydrogel achieve high mechanical properties with a compressive strength of 6.63 MPa (50%). The nanocomposite hydrogel developed here could be a promising candidate material in bionic articular cartilage substitute materials.

The Effect of Intrinsic Mechanical Properties on Reducing the Friction-Induced Ripples of Hard-Filler-Modified HDPE

Ripple deformations induced by friction on polymeric materials have negative effects on the entire stability of operating machineries. These deformations are formed as a response to contacting mechanics, caused by the intrinsic mechanical properties. High-density polyethylene (HDPE) with varying silicon nitride (Si3N4) contents is used to investigate different ripple deformation responses by conducting single-asperity scratch tests. The relationship between the intrinsic mechanical properties and the ripple deformations caused by filler modifications is analyzed in this paper. The results show the coupling of the inherent mechanical properties, and the stick-slip motion of HDPE creates ripple deformations during scratching. The addition of the Si3N4 filler changes the frictional response; the filler weakens the ripples and almost smoothens the scratch, particularly at 4 wt.%, but the continued increase in the Si3N4 content produces noticeable ripples and fluctuations. These notable differences can be attributed to the yield and post-yield responses; the high yield stress and strain-hardening at 4 wt.% provide good friction resistance and stress distribution, thus a smooth scratch is observed. In contrast, increasing the filler content weakens both the yield and post-yield responses, leading to deformation. The results herein reveal the mechanism behind the initial ripple deformation, thus providing fundamental insights into universally derived friction-induced ripples.

Applications of Hydrogel with Special Physical Properties in Bone and Cartilage Regeneration

Hydrogel is a polymer matrix containing a large amount of water. It is similar to extracellular matrix components. It comes into contact with blood, body fluids, and human tissues without affecting the metabolism of organisms. It can be applied to bone and cartilage tissues. This article introduces the high-strength polymer hydrogel and its modification methods to adapt to the field of bone and cartilage tissue engineering. From the perspective of the mechanical properties of hydrogels, the mechanical strength of hydrogels has experienced from the weak-strength traditional hydrogels to the high-strength hydrogels, then the injectable hydrogels were invented and realized the purpose of good fluidity before the use of hydrogels and high strength in the later period. In addition, specific methods to give special physical properties to the hydrogel used in the field of bone and cartilage tissue engineering will also be discussed, such as 3D printing, integrated repair of bone and cartilage tissue, bone vascularization, and osteogenesis hydrogels that regulate cell growth, antibacterial properties, and repeatable viscosity in humid environments. Finally, we explain the main reasons and contradictions in current applications, look forward to the research prospects in the field of bone and cartilage tissue engineering, and emphasize the importance of conducting research in this field to promote medical progress.