Robust low friction mechanism of HNT-PVPA composite coating based on microviscosity regulation

Reducing the coefficient of friction is a critical method for artificial implants to improve service life and enhance efficiency. Maintaining a robust low-friction effect is essential for optimal artificial implant performance. This paper utilizes the mechanism of the interaction between interfacial charge and microviscosity to design a composite coating for titanium alloy modified with halloysite nanotubes/PVPA. The friction coefficient of the composite coating-PTFE system is stabilized at a low friction state of about 0.008, with an 13.40% improvement in load-bearing capacity compared to pure PVPA coating. This low-friction state is maintained over a wide range of speeds and for extended periods. Further, the study reveals that the electrical property differences between the inner and outer walls of the halloysite nanotubes induce specific aggregation of anions and cations. These ions increase the microviscosity around the tube wall by forming hydrogen bonds with water molecules and attracting water molecules to form hydronium cations, contributing to the low-friction mechanism. The halloysite nanotube/PVPA composite coatings also enhance the coating's toughness in the body fluid environment by stabilizing the crosslinked core region against perturbations from multivalent cations. The results provide a new approach to achieving low-friction composite polymer coatings with improved frictional properties in biotribology