Diffusion layer contact angle tests

Once the durability testing of the fuel cells is finalized, the internal components are then characterized. For diffusion layers, some of these characterization techniques include SEM to visualize surface changes, porosimetry measurements to analyze any changes in porosity within the DL and MPL, IGC (inverse gas chromatography) to identify relative humidity effects on the hydrophobic properties of the DLs, contact angle measurements to observe any changes in the hydrophobic/hydrophilic coatings of the DL, etc. [254,255]. 

The transfer of hydrophobicity onto solid pollution layers is possible by the diffusion of LMW that is contained in the silicone elastomers. This means that LMW diffuses into this layer and is lost when the layer is removed. In service this can be caused by wind or rain. To enable comparison of different materials, it was found useful to evaluate the dynamics of this process by measuring the dynamic contact angles on the surface of such pollution layers. For the tests, the procedure with a pollution layer of fumed silica described in [9] was used. With respect to a lifetime of high-voltage outdoor insulators of at least 25 years, we have to ask at the same time for the long-time effects and the repeatability of the transfer effect. 

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