Achievement of Super-Low Friction between Ultra-polished Quartz Lubricated by Hydrated Hydroxyethyl Cellulose

The hydroxyethyl cellulose (HEC) is a biocompatible and nonperishable natural compound, which makes it an ideal additive for achieving super-low friction in hydration lubrication. In this work, ultra-polished quartz glasses were used as friction pairs with a contact area as large as 50.24 mm². The lubrication behavior of HEC solutions was studied and the topology of the friction pairs was investigated. A super-low COF of 0.0012 was achieved under lubrication of 1.00 wt.% HEC. Increasing or decreasing the dosage of HEC will lead to defective lubrication. Dehydration tests have shown that saturated salts compete for the water of the hydrated HEC and destroy the lubricating film, demonstrating the importance of hydration in achieving super-low lubrication. The XPS spectra of quartz and quartz covered with lubricant indicate that there is no chemical interaction between the quartz and HEC during the friction. However, a negative shift in the peak of O 1s lines were detected, suggesting that physical adsorption of the oxygen atoms occurs at the interface between the quartz and the lubricant. The lubrication regime was analyzed by Hamrock-Dowson theory and the ratio λ is around 1.7–24.5, which suggested that the lubrication regime was mixed lubrication or hydrodynamic lubrication. According to the experiments and discussions, possible lubrication models are proposed for HEC lubricants with different concentrations, which can contribute to the development of new hydration lubricants with superlubricity properties and are of great importance for scientific exploration and engineering applications.