Comparison of nanostructure and nanomechanical properties of cast and air sides of polyimide films from different manufacturers

Polyimide films are widely applied in harsh environments because of their outstanding performance. Highquality polyimide films are often manufactured through a two-step process. The complicated procedure results in different properties on the two sides, i.e., the air side and cast side of the films, and the quality of products from different manufacturers varies notably. In the present work, polyimide films with two thicknesses (1 and 2 mm) from four manufacturers were investigated. Atomic force microscope and FT-IR spectrometer were employed to monitor morphology, roughness, nanomechanical properties, and corresponding relative imidization degree on the two sides of each film. Statistical tools were applied to analyze the data. T-test suggests that the two sides of the same film were significantly different in roughness, DMT modulus, and relative imidization degree (p < 0.05). The roughness on the air side was consistently smaller than that of the cast side. ANOVA was used to compare differences among the manufacturers. Manufacturer B provided the smoothest films with the highest DMT moduli and imidization degrees. A positive correlation was found between the DMT modulus and imidization degree (r = 0.7330). Nanostructure and nanomechanical properties could affect the quality of the film. Striped morphology and adhesion were found on the cast side of the 2-mm film from manufacturer D, which compromised the film tension in the direction perpendicular to the strips. Investigations of morphology and mechanical properties of polyimide film at the nanoscale would help us better characterize the film, assure its quality, and select suitable film and side for proper applications.