Super-low friction of thermal-treatment-concentrated polymer brushes (TT-CPBs) under boundary lubrication: A practical method to shorten the swelling time of CPBs in solvents

Abstract

Concentrated polymer brushes (CPBs) are a class of thin polymer films that are composed of polymer chains densely grafted to substrate surfaces. Due to their excellent tribological performance derived from the highly stretched conformation of the polymer chains in suitable solvents, CPBs are expected to be applicable as tribological coatings in sliding components. However, a long swelling time is required to obtain fully swelled CPBs in solvents. To overcome this issue, we propose a simple method involving thermal treatment of CPBs in solvents. Our results showed that this method can dramatically reduce the swelling time of CPBs from more than 48 h to less than 3 min. Moreover, thermal-treatment-CPBs (TT-CPBs) can provide an extremely low friction coefficient (0.002) under the boundary lubrication regime at the TT-CPB/steel tribo-pair interface. All our results suggest that the thermal treatment method is a practical method that will allow the industrial application of CPBs.