Fabrication of polyelectrolyte brush-functionalized two-dimensional covalent organic frameworks as additives for aqueous lubricants

A polyelectrolyte brush-functionalized COF nanosheets exhibiting fine dispersion stability in water were successfully prepared via UV-induced thiol-ene “click” reaction for initiator binding and subsequent surface-initiated ATRP for polyelectrolyte brush grafting. The as-prepared TD-COF-PSPMA, as water-based lubricant additive, appears as an effective agent to reduce friction and wear; the average friction coefficient of the lubricant decreases to 0.173 from 0.596 under 5 N and 0.5 wt% addition concentration. The advantage of TD-COF-PSPMA is the efficient adsorption of anion groups to the positively charged iron surface, which is beneficial to the formation of a tribo-chemical protective film over the worn surface. Moreover, the presence of hydration layer confined with polyelectrolyte brushes is conducive to friction reduction, resulting in the remarkable lubrication performance.