Development of a semi-empirical model to describe the temperature-dependent permeation mechanisms through plasma-polymerized barrier layers

• Applicant: Professor Dr. Rainer Dahlmann
• Subject Area: Plastics Engineering
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 542661390

Due to their molecular structure, plastics have a comparatively high permeability to gases and vapors, which must be reduced for certain applications such as food packaging or the enclosure of electronics. Various methods have been developed to achieve a barrier effect, for example by using multilayer films with barrier materials such as ethylene vinyl alcohol (EVOH) or by using oxygen absorbers. However, most of these barrier technologies require large quantities of additives so that the product no longer consists of a mono-material. The application of plasma-enhanced chemical vapor deposition (PECVD) barrier layers, on the other hand, requires only small amounts of foreign substances, so that the product can still be considered a monomaterial in terms of its recyclability and can therefore be recycled much more easily. To date, PECVD barrier layers have mostly been developed empirically and based on experience. Precise adjustment of the permeation requires a systematic development process for coatings in which the essential mechanisms of mass transfer are considered. In addition, the sustainability of coating development processes can be improved by reducing energy consumption and the use of reactants. This is where the proposed research project comes in. The description of permeation through thin films containing defects has so far been limited to defects in the µm range - defects in the nm range have hardly been considered due to their small size, although their importance has been known for some time. The investigation of these pores is now possible using positron annihilation spectroscopy (PAS) and has been used successfully. It therefore seems logical to use PAS data to develop a model to describe the permeation processes. For this purpose, PECVD layers with different porosities are generated and characterized. Based on the data, pore structures are generated in order to obtain a geometric model of the layer. In addition to the porosity, the temperature-dependent permeation behavior of different gases is also considered, as this allows conclusions to be drawn about the interaction of the gases with the coating. Using the geometric model, different sorption and diffusion mechanisms are investigated in order to find a suitable description of the permeation processes, taking into account the measured mass transfer rates. This should enable the virtual optimization of layer properties, which can then be transferred to real systems. The successful implementation of such a model provides a basis for further research into permeation mechanisms with reduced time and resource input.

• DFG Programme: Research Grants