A new tool for characterising water permeation across films

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The growing sector of optoelectronics (e.g. organic light emitting diodes and organic photovoltaic devices) requires the development of transparent materials to protect the circuitry from moisture. Assessing the permeation of water through such materials is, therefore, a key factor in product development. As a result, there is an increasing interest in understanding water permeation and how this varies with different thin film materials.

Researchers at the University of Oxford have conceived a new method to study water vapour permeation through films. The technique allows the determination of the degree of permeation and the mechanism by which it occurs. Sample preparation is also simple and can be carried out without the need for a dry box or clean room.

The threat of humidity

Water poses an inherent hazard to many technologies and industrial processes. A plethora of different protecting barriers or films has been devised and implemented to fit the needs of specific applications. A key example of this is in the field of optoelectronics where films are necessary to protect organic light emitting diodes (OLEDs) used in mobile phone screens.It is of utmost importance to understand how water vapour permeation through these films may occur in order to improve their performance.

Finding the leaks in the current methods

Various methods are currently used to assess water vapour transmission rate (WVTR) through films but none of them present a satisfactory combination of sensitivity, accuracy, reliability and low cost. The electrical Ca test represents a promising methodology. The test relies on a metal Ca plate in contact with the film, which undergoes a change in electrical conductivity when the moisture permeates the film. Unfortunately, the preparation of samples is very cumbersome, requiring the use of a dry box and therefore is expensive to implement.

Increasing accuracy and simplicity

Academics from the University of Oxford have developed a new version of the Ca test that improves its accuracy and overall performance. The method uses a camera to record the build-up of calcium hydroxide on the Ca plate caused by the moisture that permeates across the film. Furthermore, it gives additional information about the mechanisms of permeation (macrodefects or background/nanodefects) allowing better material designs and production controls.

Sample preparation has also been simplified and the need for the use of an inert atmosphere removed.

Advantages of the Oxford technology

Other main advantages of using our technology are:

  • High sensitivity
  • High throughput
  • Control of test environmental conditions
  • Facile sample preparation


This technology is under patent protection and the University is looking for investors willing to help in its development and commercialisation.

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