Fraunhofer IVV: How to measure ultra-low water vapour permeation faster
Permeation measurements are often a bottleneck for the development of high barrier films required for flexible electronic devices and vacuum insulation panels. The reasons are long measuring times, restricted measuring conditions and specific constants, such as sorption and diffusion coefficients, which cannot be easily read out from results. Physics cannot be cheated, but with some clever use of mathematics, testing conditions and testing devices, tests can be accelerated:
1.) By use of numerical simulation, permeation coefficients can already be calculated before steady state is reached.
2.) Measurements can be done at higher temperatures.
3.) More samples can be measured at the same time in parallel.
To be able to measure faster, the German Fraunhofer Institute for Process Engineering and Packaging IVV developed and tested a new ultra-low permeation measurement device based on a constant-flow carrier-gas-system to measure both the transient and stationary water vapour permeation through high-performance barrier films. Very low water vapour transmission rates (WVTRs) down to 2 x 10-5g / (m² d) at a controlled relative humidity within the range of 15%–90% can be measured.
Measuring times can be shortened by calculating the permeation coefficients already from transient state, by measuring at higher temperatures (temperature range of 23-80 °C) and by measuring more samples in parallel. The Fraunhofer device has 30 measurement cells. This approach allows shortening the very long permeation measurement times for multilayer high barrier structures from many months to only a couple of weeks. These results also support to design multilayer stacks according to the water vapour barrier requirements of the final application and to the targeted product lifetime. The optimisation of the multilayer architecture, in terms of the layer sequence and the thicknesses, avoids the high costs due to over- or under-packaging. The testing procedures and device are now available to other research groups in academia and industry.
Klaus Dieter Bauer, Fraunhofer IVV
Caption: Barrier films are the centrepiece in recent research at Fraunhofer IVV (photo: Fraunhofer IVV)