Barrier Web 2009 Holger Nörenberg, Technolox Ltd., Oxford, UK Measurement of Water Vapour Permeation: Current State of the Art and Future Challenges “We invent and build permeation measurement equipment”

Barrier Web 2009 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

Barrier Web 2009 Diffusion D = Solubility S & Permeation P Current State of the Art Fickian Diffusion: P=D·S

Barrier Web 2009 Applications of Barrier Layers Flexible OLED displays Lighting Photovoltaics E-paper Thin-film devices (batteries,…)

Barrier Web 2009 Measurement of … g/m 2 /day: We are getting there Calcium Test Tritium Test MOCON Aquatran Technolox Deltaperm

Barrier Web 2009 Optical Calcium Test Observation of the corrosion of a thin calcium layer Position-resolved information Parallel processing

Barrier Web 2009 Electrical Calcium Test Monitoring conductance and 1/f noise during Ca-degradation Sensitivity <10 -6 g/m 2 /day

Barrier Web 2009 Tritium Test Sensitivity g/m 2 /day

Barrier Web 2009 MOCON Aquatran Detection limit: 5x10 -4 g/m 2 /day H 2 O in Carrier gas (N 2 ) Coulometric sensor

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

Barrier Web 2009 Raw Data Information Contents: Rate of Permeation ~ Slope of  p=f(t)

Barrier Web g/m 2 /day and below Inorganic barrier on 100  m PEN- substrate Information Contents: WVTR=f(T) “Activation Energy” Can be (carefully) used for interpolation or extrapolation (“accelerated testing” 40 o C

Barrier Web 2009 Deltaperm -5 g/m 2 /day low noise level Challenge: reduce or understand background signal

Barrier Web 2009 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

Barrier Web 2009 Sensitivity: How small is g/m 2 /day? x 0.1 x 3652 = 3.7x10 -4 g WV fits into a water droplet of Ø 0.9 mm Typical substrate: 100  m thick polyester (PET, PEN) S=0.005g WV /g PET 3x10 -3 g WV /m 2 (RH=50%) g/m 2 /day

Barrier Web 2009 ABCD Sample Conditioning Both sides of sample under ambient conditions Upstream side exposed to water vapour (RH=0.9) Downstream side of sample under vacuum

Barrier Web 2009 Single Barrier Sample can initially take up water

Barrier Web 2009 Multilayers WVTR may fall first and increase later

Barrier Web 2009 Time-lag Information Contents: Rate of Permeation, Diffusion Coefficient, Solubility WV through

Barrier Web 2009 Some Theory D = L 2 /6t lag Transient conditions: Stationary conditions: P = const S= This algorithm works for ideal gases and homogeneous materials Multilayers: system of differential equations

Barrier Web 2009 Outgasing of WV Uptake of WV time

Barrier Web 2009 PET or PEN Outgasing: Water Vapour leaves the Sample US 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

Barrier Web 2009 PET or PEN Water Vapour enters the Sample 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

Barrier Web 2009 Conclusions Various methods method suitable to measure WVTR in the … g/m 2 /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!