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Holger Nörenberg, Technolox Ltd. , Oxford, UK technolox

Measurement of Water Vapour Permeation: Current State of the Art and Future Challenges. “We invent and build permeation measurement equipment”. Holger Nörenberg, Technolox Ltd. , Oxford, UK www.technolox.com. Problem: How to ensure a sufficiently long lifetime

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Holger Nörenberg, Technolox Ltd. , Oxford, UK technolox

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  1. Measurement of Water Vapour Permeation: Current State of the Art and Future Challenges “We invent and build permeation measurement equipment” Holger Nörenberg, Technolox Ltd. , Oxford, UK www.technolox.com

  2. Problem:How to ensure a sufficiently long lifetime of flexible electronics to make money • Key Aspect:Failure due to ingress of water vapour • Solution:Barrier layer to prevent ingress of water vapour • Good Barrier?Measurement of the permeation of WV • Problem 1:Very small amount of water vapour to be measured • Problem 2: Short Measurement time, easy operation

  3. Current State of the Art Solubility S & Diffusion D = Fickian Diffusion: P=D·S Permeation P

  4. Applications of Barrier Layers • Flexible OLED displays • Lighting • Photovoltaics • E-paper • Thin-film devices (batteries,…)

  5. Measurement of 10-4 … 10-6 g/m2/day: We are getting there • Calcium Test • Tritium Test • MOCON Aquatran • Technolox Deltaperm

  6. www.vitexsys.com Optical Calcium Test • Observation of the corrosion of a thin calcium layer • Position-resolved information • Parallel processing

  7. Electrical Calcium Test • Monitoring conductance and 1/f noise during Ca-degradation • Sensitivity <10-6 g/m2/day • www.imre.a-star.edu.sg

  8. Tritium Test • Sensitivity 10-6 g/m2/day • www.ga.com

  9. MOCON Aquatran • Detection limit: 5x10-4 g/m2/day • www.mocon.com H2O in Carrier gas (N2) Coulometric sensor

  10. Total Pressure Method valve upstream side Water vapour upstream side Water vapour 2: Admission of water vapour to the upstream side. pump OFF sample Pump ON sample pressure sensor downstream side downstream side PC 3: Measuring the total pressure p(t) means of a pressure sensor. upstream side Water vapour Pump OFF sample pressure sensor downstream side p t 1: Evacuation of upstream side and downstream to remove the ambient air • Sensitivity: <2x10-4 g/m2/day • suitable for gases and vapours • wide parameter range (100oC)

  11. Raw Data • Information Contents: Rate of Permeation ~ Slope of Dp=f(t)

  12. Inorganic barrier • on 100mm PEN- • substrate 10-4g/m2/day and below 40oC • Information Contents: WVTR=f(T) “Activation Energy” • Can be (carefully) used for interpolation or extrapolation (“accelerated testing”

  13. Deltaperm Sensitivity • @5x10-5 g/m2/day low noise level • Challenge: reduce or understand background signal

  14. Challenges • Sensitivity • Sample conditioning - Measurement time • Distinguishing between good barriers caused by a long time-lag or by low permeability • Parameter range of measurement (temperature, RH): valuable tool • Interpretation of “unwanted effects” (background signal, noise, edge permeation, outgasing, …) • Easy operation • Theoretical understanding of the permeation process

  15. Sensitivity: How small is 10-6g/m2/day? • 10-6 x 0.1 x 3652 = 3.7x10-4g WV • fits into a water droplet of Ø 0.9 mm • Typical substrate: 100 mm thick polyester (PET, PEN) S=0.005gWV/gPET 3x10-3 gWV/m2 (RH=50%) 10-6 g/m2/day

  16. Sample Conditioning A B C D Both sides of sample under ambient conditions Upstream side exposed to water vapour (RH=0.9) Downstream side of sample under vacuum

  17. Single Barrier • Sample can initially take up water

  18. Multilayers • WVTR may fall first • and increase later

  19. WV through PEN @23ºC Time-lag • Information Contents: Rate of Permeation, Diffusion Coefficient, Solubility

  20. S= Some Theory • Transient conditions: D = L2/6tlag • Stationary conditions: P = const • • This algorithm works for ideal gases and homogeneous materials • Multilayers: system of differential equations

  21. Outgasing of WV Uptake of WV time

  22. Outgasing: Water Vapour leaves the Sample US PET or PEN DS • Water vapour leaves the • sample (outgasing) • After some WV has accumulated • outside the sample it is removed • with a vacuum pump • More WV leaves the sample • WV removed again • And so on • Pressure increase due to outgasing • is summed up and the total amount • of WV coming from the sample • is then calculated

  23. Water Vapour enters the Sample PET or PEN • A dry sample is exposed to water • vapour • Sample takes up WV • More WV is admitted • Sample takes up more WV • And so on • The pressure decrease of the • WV is summed up and used to • calculate the amount of WV that • has gone into the sample

  24. Conclusions • Various methods method suitable to measure WVTR in the 10-4 … 10-6 g/m2/day-range • Wealth of information from permeation measurement • Measurement under stationary and transient conditions • Valuable tools: T, RH • Outgasing • Theoretical calculations should complement experimental work • A lot of challenges remain !!! Thank you very much for your attention!

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