Controllable superlubricity achieved with mixtures of green ionic liquid and glycerol aqueous solution via humidity
Jing Hua, Marcus Björling, Roland Larsson, Yijun Shi
Abstract
In this work, superlubricity between steel surfaces lubricated by mixtures of [Choline][Proline] ([Cho][Pro]) ionic liquid and glycerol aqueous solution has been reached by using a rotating tribometer. Stable superlubricity could be obtained even under the humidity between 7 and 9% RH. The lowest friction is observed when the lubricant contains 3 wt% ionic liquid. It is found that adding 3 wt% [Cho][Pro] is helpful to maintain enough water in the steady period to retain a low viscosity. According to the calculation, the superlubricity achieved in thin film lubrication region, which is attributed to the stern layer formed by [Cho][Pro] and hydrogen-bond network that enabled a thin water layer at the interface. Interestingly, it is observed that humidity can be used to control lubrication state between superlubricity and non-superlubricity. This study provides a new method to accomplish switchable superlubricity under low humidity.