Improved Tribological Performance of Polydopamine/Polytetrafluoroethylene Thin Coatings With Silica Nanoparticles Incorporated into the Polydopamine Underlayer

Abstract

Polytetrafluoroethylene (PTFE) is a solid lubricant with low friction coefficient. However, it lacks durability as a thin coating. Prior studies have shown that a polydopamine (PDA) underlayer enhances the coating durability. In this study, 100, 200, and 300 µL of aqueous silica nanoparticle (NP) dispersions were added to a 15 mL PDA deposition solution. Stainless steel substrates were coated with PDA + silica in the mixed dispersions and then coated with PTFE layers to form thin PDA + silica/PTFE coatings. The coatings were tested in ball-on-flat linear reciprocating motion under dry contact conditions. The durability of the PDA/PTFE coating was improved by 70% when 100 µL of aqueous silica NP dispersion was added. The significant improvement in the durability was attributed to the increased adhesion of the PTFE coating to the PDA underlayer, the fragmented wear debris, and the enhanced counterface transfer film. These samples also showed enhanced resistance under linearly increasing load scratch testing with lower coefficient of friction (COF) and higher delamination resistance when compared to samples without silica.