A sulfonated modification of PEEK for ultralow friction

Abstract

Polyether ether ketone (PEEK) is a widely used material for friction pairs due to its excellent mechanical strength, good wear resistance, and chemical inertness. However, some modifications are necessary when PEEK is used as a water-lubricated friction pair. In this study, a novel sulfonation method was developed to design a water-lubricated friction pair with ultralow friction, good wear resistance, and high loading capacity. PEEK powders were sulfonated using ClSO3H and sintered to form bulk plastic. The sulfonated PEEK (SPEEK) plastic exhibited good tribological properties. At a low sliding speed, the friction coefficient was smaller than 0.02 when a 3 wt% NaCl solution was used as the lubricant. The order of magnitude of the wear rate was as low as 10−8 mm3/(N·m). The mechanism of friction reduction was mainly hydration lubrication. The negatively charged −SO3− groups on the friction pair can adsorb hydrated Na+ cations by electrostatic interactions. These hydrated Na+ cations have a high load capacity and low shearing resistance. The ultralow wear mechanism observed in this study is possibly due to ultralow friction properties of the friction pairs prepared through the proposed sulfonation and thermoforming procedures.

Electric Potential Controlled Ionic Lubrication

“…It was found that EDL exhibited obvious 3D reconfiguration under different electric potentials. In addition, polymeric ionic liquids (PILs) adsorbed on a charged Au (111) surface can form a cation-enriched boundary layer that lubricates the interface, and the adhesion characteristics are closely related to the applied electric potential [101]. Figure 5b shows the normal force versus separation distance curves between the SiO2 probe and gold surface in NaCl solution under different applied potentials using EC-AFM.…”

“…The ions in water-based lubricants can form an adsorption layer through the electrostatic interaction, which can bear a large applied load and reduce friction at the interface. Ionic aqueous lubricants even provide favorable conditions for the realization of superlubricity under all lubrication regimes, including boundary lubrication (BL) [69,82,[110][111][112][113][114], mixed lubrication (ML) [14,45,55,107,115,116], and elastohydrodynamic lubrication (EHL) [46,[117][118][119][120]. In a BL regime, the repulsive force (like hydration repulsion) generated by the adsorption of ions on the friction surfaces is conducive to bearing the applied load and reducing the friction.…”

“…Various experiments have proved that the active control of friction can be effectively achieved by controlling the structure of the adsorption layer and the interaction between IL and friction surfaces by applying an electric potential. Rob Atkin group [123][124][125][126][127][128] focuses on the interactions in different ionic liquids on Au (111) or pyrolytic graphene (HOPG) surfaces. It has been found that ionic liquids rearrange on the surface of the substrate under applied potential.…”

A Systematic Review of the Recent Advances in Superlubricity Research

“…Currently, there are still many constraints for solid-state superlubricity to move towards practical application, such as demanding environmental conditions (vacuum, inert gases, etc. ), super-clean and perfect crystal surfaces that are difficult to realize at the macroscopic scale, and the inability to withstand high loads, and so on [179][180][181][182][183]. In contrast, liquid superlubricity is expected to realize engineering applications earlier than solid superlubricity due to relatively low environmental requirements and high load-bearing capacity.…”

Tribological Behavior of Sulfonated Polyether Ether Ketone with Three Different Chemical Structures under Water Lubrication

“…The former utilizes sulfonation reagents (concentrated sulfuric acid and chlorosulfonic acid) for direct sulfonation, while the latter utilizes sulfonated monomers. Yuan et al [29] successfully obtained SPEEK with ultra-low friction coefficient through sulfonation using chlorosulfonic acid and sintering via a sparking plasma sintering (SPS). Wu et al synthesized a novel bisphenol-A (BPA)-type sulfonated PEEK and compounded it with 10 wt% carbon fiber, which exhibited a friction coefficient as low as 0.009 and a wear rate of grade 10 −8 when a 3 wt% NaCl solution was used as the lubricant at a low sliding speed (0.10 m/s) [30].…”