The Effects of PTFE Thickness on the Tribological Behavior of Thick PDA/PTFE Coatings

In this study, the effects of polytetrafluoroethylene (PTFE) thickness on the wear and friction properties of spin-coated PTFE and polydopamine (PDA)/PTFE coatings on stainless steel (SS) substrates were investigated. The PTFE coating thickness was varied by controlling the number of PTFE spin-coating deposition cycles. The PDA/PTFE coatings showed 1.4 to 4.9 times the wear life of that of the PTFE coating deposited at the same number of PTFE spin-coating cycles. The coefficients of friction and water contact angles of the PDA/PTFE coatings were found to be slightly higher than those of the PTFE coatings due to higher surface roughness. The addition of a PDA underlayer helped the PTFE to adhere more strongly to the SS substrate, which contributed to the coatings' improved durability. The durability of the PDA/PTFE coating increased sharply when the PTFE thickness exceeded 30 μm. Notably, a 42-μm-thick PDA/PTFE coating had 105 times the wear life of that of a 3-μm-thick PTFE coating. The enhanced transfer film on the counterface and the larger contact area for supporting the load were responsible for the extended durability of the thicker coatings.