Correlation Between Evaporation Dynamics and Self-Healing Characteristics in Metallised Polypropylene Films

Abstract

The morphology and structure of electrodes play a pivotal role in determining the self-healing performance and current-carrying capacity of metallised biaxially oriented polypropylene (BOPP) films. An experimental setup replicating the industrial vacuum evaporation process and a custom-designed self-healing testing platform were specifically developed to systematically investigate the influence mechanisms of key evaporation parameters, including evaporation rate and evaporation thickness. As the evaporation rate increases from 2 to 5 $\AA$/s, both the self-healing area and energy are enhanced, whereas the edges of the self-healing morphology exhibit more pronounced fractal characteristics. At the microscale, low evaporation rates reduce and homogenise the micro-level current and decrease the invasion proportion of Al elements into the BOPP substrate. Notably, the metal growth mechanism on the surface of BOPP was clearly demonstrated through atomic force microscopy (AFM) to follow the representative ‘isolated metal islands’ model, resulting in varying current-carrying modes under different electrode thicknesses. Thicker electrodes exhibit significantly enhanced current-carrying capacity, accompanied by a simultaneous increase in self-healing area and energy. Finally, a surface model based on the Gaussian random function was constructed to numerically investigate the impact of surface roughness on current distribution, providing an explanation for the observed self-healing phenomenon.