Annealing effect on the structure relaxation and mechanical properties of a Polytetrafluoroethylene film by RF-magnetron sputtering

In the current work, a Polytetrafluoroethylene (PTFE) film with thickness of 3.4 μm was prepared by RF-magnetron sputtering on a silicon substrate. By annealing at different temperatures (100–300 °C), the structure relaxations of PTFE film were systematically investigated via the variations of physical properties, i.e., atomic bonding, density and surface morphology. It was unfolded that inner atomic arrangement and surface morphology changed little whilst film density was greatly increased with increasing annealing temperature. Relying on nanoindentation technology, the mechanical properties including hardness, elastic modulus, creep resistance and friction coefficient were measured in the as-prepared and annealed PTFE films. By increasing annealing temperature, hardness and elastic modulus were enhanced at 100 °C and then gradually declined at higher temperatures. The room-temperature creep resistance was promoted in the annealed films and nearly independent on annealing temperature. During the scratch test, the residual depth of scratches increased and the elastic recovery ratio decreased by further increasing annealing temperature.