Investigation of the mechanisms for stable superlubricity of poly(vinylphosphonic acid) (PVPA) coatings affected by lubricant

Abstract

Abstract:The stability of the tribological properties of polymer coatings is vital to ensure their long term use. The superlubricity of the poly(vinylphosphonic acid) (PVPA)-modified Ti6Al4V/polytetrafluoroethylene (PTFE) interface can be obtained when lubricated by phosphate-buffered saline (PBS, pH = 7.2), but not when lubricated by deionized water and ethanol. Therefore, the mechanisms for the superlubricity of PVPA coatings affected by lubricant were investigated in detail. The stability of the PVPA coatings and their compatibility with the lubricant are critical factors in realizing ideal tribological properties of PVPA coatings. Robust PVPA coatings are stable under a wide range of pH values (6-10) using PBS as the basic solution, and are also characterized by superlubricity. The hydrolysis kinetics of phosphate anhydride is the main reason for the pH responses. In addition, along with stability, PVPA coatings exhibit different friction coefficients in salt solutions which are composed of various ions, which indicates that the compatibility between PVPA coatings and the lubricant can be used to regulate the superlubricity properties. Based on a fundamental understanding of the mechanism of surperlubricity by considering the effects of the lubricant, PVPA coatings with stability and perfect tribological performance are expected to be applied in more aspects.

Physicochemistry aspects on frictional interfaces

“…At present, superlubricity materials include solid lubricants (diamond like carbon (DLC), molybdenum disulfide (MoS 2 ), etc.) [88][89][90] and liquid lubricants [91][92][93][94][95][96][97]. The solid lubricants have been studied in detail by molecular dynamics simulations and experimental investigations.…”

Molecular self‐assembly and morphology induction in high‐performance aromatic phosphonated block copolymers

“…In natural occurring biomaterials, the morphological control is done in a fascinating way via various interactions such as ionic and hydrogen bonds. However, for the artificial molecules, a proper adjustment of chemical groups, size, and chemical process is required to allow the molecules to produce a desired shape upon self‐assembly . In this regard block copolymers with an ability to phase separate due to their dissimilar chemical contents can resolve the issue of having a controlled morphology .…”

“…However, for the artificial molecules, a proper adjustment of chemical groups, size, and chemical process is required to allow the molecules to produce a desired shape upon self‐assembly . In this regard block copolymers with an ability to phase separate due to their dissimilar chemical contents can resolve the issue of having a controlled morphology . In these materials, a strong repulsion between two unlike segments of block copolymer may usually result in microphase separation leading to columnar, lamellar, bicontinuous, and gyroid types of morphologies .…”

“…In this regard block copolymers with an ability to phase separate due to their dissimilar chemical contents can resolve the issue of having a controlled morphology . In these materials, a strong repulsion between two unlike segments of block copolymer may usually result in microphase separation leading to columnar, lamellar, bicontinuous, and gyroid types of morphologies . In the bulk, the phase separation between different chemically immiscible blocks and the chemical bonds constraints govern the formation of ordered domains.…”

“…One class of polymers known as poly(phosphoester)s have been receiving attention due to their biodegradable properties for biomedical applications. Copolymers based on poly(phosphoester)s, for example, poly(ethylene alkyl phosphonate) have been suggested to show a phase transition from single chain to macroscopic coacervates in aqueous media. These polymers were investigated for their aggregates formation and thermoresponsive behavior.…”