Mechanochemical preparation of zwitterionic polymer functionalized covalent organic frameworks as water-based lubricant additives

In this paper, we report the successful synthesis of the zwitterionic polymer PEIS functionalized covalent organic frameworks (COFs), abbreviated as LZU1-PEIS, via two mechanochemical means, namely tribochemical reaction and ball milling, denoted as LZU1-PEIS-TC and LZU1-PEIS-BM, respectively. The LZU1-PEIS can be derived when a mechanochemical-driven Schiff base reaction occurs between the aldehyde-terminated COFs and the rich amino-terminated zwitterionic polymers. On account of their two-dimensional nanoscale structure, easiness to shear, and superior hydration capability, the as-prepared LZU1-PEIS manifested remarkable tribological properties as water lubricant additives. The average friction coefficients were reduced from 0.67 to 0.31 (LZU1-PEIS-TC) and 0.23 (LZU1-PEIS-BM), respectively. Furthermore, the formation of a physical protective film fabricated via deposition of the nano-additives and tribochemical reaction is instrumental in curtailing friction and wear. Our research focuses on the preparation of functionalized COFs as lubrication additives, and offers a credible experience and promising design contemplation toward lubricating materials.