The effects of annealing conditions on the wear of PDA/PTFE coatings

The effects of annealing conditions on the micro-wear properties of polydopamine (PDA)/polytetrafluoroethylene (PTFE) coatings were studied using atomic force microscopy (AFM) and molecular dynamics (MD) and coarse-grained simulations. It was found that annealing at 372 degrees C for 4 min and 8 min caused columnar PTFE particles to elongate into spindle shapes and bind together more tightly than the 0 min annealing sample, which increases the adhesion between PTFE particles and thus the wear resistance of the PDA/PTFE coatings. However, larger islands formed on the 8 min annealing sample make them easily be scraped off, resulting in more wear at the initial scratch stage than the 4 min annealing sample. Longer annealing duration also caused the degradation of PTFE chain structure, which weakens the strength of the PTFE molecular chain and makes the folded structure in the spindle-shaped PTFE particles more readily pulled out to form fibers. Moreover, more weakly bond paralleled spindle-shaped PTFE particles were formed in the sample with longer annealing duration making the coatings less wear resistant. These results show that controlling the final annealing duration of PDA/PTFE coatings is an effective approach for the fabrication of highly durable PTFE coatings.