Examination of ionic diffusion permeability of polyimide thin films

Abstract

Materials based on polyimide show a wide range of use in electrical engineering, for example as isolation and protection medium. Nevertheless, ions can penetrate such layers, which leads to corrosion and to deterioration of the system. Consequently, it is important to understand the interaction between ions and polymer layers.In this project, polyimide layers were produced, and their thicknesses determined. Subsequently, these layers were integrated into a diffusion cell. In this cell, the polymer was used as a separator for two different concentrated salt solutions. The diffusion leaded to a reduction of potential difference, which can be measured. Furthermore, a Laser Ablation Induced Coupled Plasma Mass Spectrometer (LA ICP MS) was used to examine diffusion profiles and elemental distributions on the surface of these layers.During this project, a new method for determining layer thicknesses and for producing more homogeneous polyimide layers were implemented. Also, Nafion® membranes were used to examine the difference when switching from a ionic highly impervious barrier to a more permeable one and to identify the osmotic impact on layers. Using polyimide P84® layers, no reproducible diffusion trend curves were obtained, despite of several optimisations. Nevertheless, most of the sources of error could be located for further improvement measures. By using LA ICP MS, conclusions about diffusion and their inhomogeneous localities were evaluated.In conclusion, several statements and propositions about mechanics of ionic diffusion using Nafion® and polyimide layers were made. For higher quality, used polyimide layer should be produced industrially. Additionally, a new method should be implemented, to fix penetrated layers on a substrate for the ablation process. The obtained results can be used for comparison with diffusion simulations and further analyses for determining diffusion mechanics in polymers.