Stofftransport Durch Schichtsysteme aus Polymeren und Dünnen Anorganischen Schichten

Flexible layer systems from polymeric substrates, thin inorganic layers deposited by vacuum coating and additional polymeric layers are frequently in use to obtain high barrier properties, predominantly against oxygen and water vapour. Especially in cases where additional polymeric coatings are able to fill defects in the in-organic layers, barrier properties of the resulting layer systems show a stronger dependence on their thickness. For the transport of condensable substances, especially of water vapour, an additional porosity in the sub-nm-size can be assigned to the inorganic layers. This, however, has a negligible effect on gas permeation. Multilayer structures made from substrates and alternating polymeric and inorganic layers show much better barrier properties than single polymeric substrates coated with single inorganic layers. These improvements, however, are less than previously reported here. Moreover, also in these cases, the condensation of water vapour in sub-nm pores gives much higher rates for the permeation of substances than expected from simple defect models.