Adhesion and surface forces in polymer tribology—A review

With the development of surface and interface science and technology, methods for the online modulation of interfacial performance by external stimuli are in high demand. Switching between ultra-low and high friction states is a particular goal owing to its applicability to the development of precision machines and nano/micro-electromechanical systems. In this study, reversible switching between superlubricity and high friction is realized by controlling the electric potential of a gold surface in aqueous salt solution sliding against a SiO 2 microsphere. Applying positive potential results creates an ice-like water layer with high hydrogen bonding and adhesion at the interface, leading to nonlinear high friction. However, applying negative potential results in free water on the gold surface and negligible adhesion at the interface, causing linear ultra-low friction (friction coefficient of about 0.004, superlubricity state). A quantitative description of how the external load and interfacial adhesion affected friction force was developed, which agrees well with the experimental results. Thus, this work quantitatively reveals the mechanism of potential-controlled switching between superlubricity and high-friction states. Controlling the interfacial behavior via the electric potential could inspire novel design strategies for nano/micro-electromechanical and nano/micro-fluidic systems.

Section: Resultsmentioning

confidence: 98%

Quantification/mechanism of interfacial interaction modulated by electric potential in aqueous salt solution

Bai

et al. 2020

“…Polymers and their composites are extensively used as tribo-engineering materials. The excellent physical and chemical characteristics of polymer-based composites make them a promising class of important tribomaterials because of their self-lubricating performance, chemical stability, superior process ability as well as cost-effectiveness [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

The effect of different layered materials on the tribological properties of PTFE composites

Song

Duan

et al. 2019

Two-dimensional (2D) lamellar materials have unique molecular structures and mechanical properties, among which molybdenum disulfide (MoS 2) and graphitic carbon nitride (g-C 3 N 4) with different interaction forces served as reinforcing phase for polytetrafluoroethylene (PTFE) composites in the present study. Thermal stability, tribological and thermomechanical properties of composites were comprehensively investigated. It was demonstrated that g-C 3 N 4 improved elastic deformation resistance and thermal degradation characteristics. The addition of g-C 3 N 4 significantly enhanced anti-wear performance under different loads and speeds. The results indicated that PTFE composites reinforced by g-C 3 N 4 were provided with better properties because the bonding strength of g-C 3 N 4 derived from hydrogen bonds (H-bonds) was stronger than that of MoS 2 with van der Waals force. Consequently, g-C 3 N 4 exhibited better thermomechanical and tribological properties. The result of this work is expected to provide a new kind of functional filler for enhancing the tribological properties of polymer composites.

“…For polymer-on-metal sliding interfaces, there is a natural propensity for the polymer material to be transferred onto the metallic counterface [45,46]. The presence of a uniform and thin transfer film is beneficial to the sliding process, because the film protects the relatively soft polymer bulk from the abrasive action of the hard asperities on the metallic surface [47,48]. The SEM micrographs of the surfaces of the steel balls after sliding against the EP resin and the composites with microcapsules are presented in Fig.…”

Section: Resultsmentioning

confidence: 99%

Ultralow friction polymer composites incorporated with monodispersed oil microcapsules

Zhang

Xie

et al. 2019

Ultralow friction polymer composites were prepared by adding oil-loaded microcapsules into epoxy (EP) resin. Mono-dispersed polystyrene (PS)/poly alpha olefin (PAO) microcapsules with a diameter of ~2 μm and a shell thickness of ~30 nm were prepared by solvent evaporation method in an oil-in-water emulsion. The lubrication behaviors of the EP resin composites with oil-loaded microcapsules have been investigated under different loads and sliding speeds. As compared with the pure EP resin, the friction coefficient of the composite could be reduced to 4% (from 0.71 to 0.028) and the wear rate could be decreased up to two orders of magnitude. It was demonstrated that the released PAO oil from the microcapsules during the friction process produced a boundary lubricating film, which could prevent the direct contact of two rubbing surfaces, and thus leading to an extremely low friction coefficient and wear rate. Moreover, the composites with microcapsules could achieve comparable lubrication properties to the case under the external lubrication condition, while the former case could effectively minimize the lubricant leakage and improve the lubrication efficiency.