Evaluation of rheological properties and tribological properties of choline/acetylamino acid ionic liquids at different frequencies

Abstract

With the increasing average lifespan of human beings, the wear and tear caused by daily activities on joints will also escalate. Consequently, there is a growing focus on the development of green, environmentally friendly, and biocompatible non-toxic lubricating materials. The presence of dual chemical active centers in natural amino acids results in anions and cations that lead to precipitation and poor lubrication effects in traditional choline amino acid ionic liquids. In this study, nine types of choline acetyl-amino acid ionic liquids ([Ch][Ac-AA]ILs) were synthesized using acetylated amino acids (Ac-AA) as anions and choline (Ch) as cations. The physicochemical properties and tribological behavior of [Ch][Ac-AA]ILs at different frequencies were evaluated. The results demonstrated that [Ch][Ac-AA]ILs exhibited excellent tribological properties and maintained effective lubrication even under high-frequency friction conditions compared to sodium hyaluronate (HA-T). This performance was attributed to the carbon chain length and functional group composition of [Ch][Ac-AA]ILs' anions. Energy dispersive spectroscopy and X-ray photoelectron spectroscopy analysis revealed that the superior lubrication performance of [Ch][Ac-AA]ILs was associated with the formation of chemical reaction films and physical adsorption films on the surface of friction pairs. This research enriches our understanding of [Ch][AA]ILs-based lubrication systems while providing valuable insights for selecting joint lubricants suitable for different activity frequencies.