The effect of temperature on the nanoscale adhesion and friction behaviors of thermoplastic polymer films.

Adhesion and friction tests were carried out in order to investigate the effect of temperature on the tribological characteristics of poly(methylmethacrylate) (PMMA) film using AFM. The pull-off and friction forces on the PMMA film were measured under a high vacuum condition (below 1 × 10(-4) Pa) as the temperature of the PMMA film was increased from 300 to 420 K (heating) and decreased to 300 K (cooling). Friction tests were also conducted in both high vacuum and air conditions at room temperature. When the temperature was 420 K, which is 25 K higher than the glass-transition temperature (T(g)) of PMMA, the PMMA film surface became deformable. Subsequently, the pull-off force increased in proportion to the maximum applied load during the pull-off force measurement. In contrast, when the temperature was under 395 K, the pull-off force did not depend on the maximum applied load. The friction force began to increase when the temperature rose above 370 K, which is 25 K lower than the T(g) of PMMA, and rapidly increased at 420 K. Decrease of the PMMA film stiffness and plastic deformation of the PMMA film were observed at 420 K in force-displacement curves. After the heating to 420 K, the coefficient of friction was measured under air condition at room temperature and was found to be lower than that measured before the heating. Additionally, the RMS roughness increased as a result of heating.