Microstructural characterization of transparent silicon oxide permeation barrier coatings on PET

The aim of this study was to correlate the microstructure and gas barrier performance of nanocomposite films. A range of SiO_x layers of varying thickness (13 to 316 nm), deposited by electron beam evaporation on polyethylene terephthalate substrates, have been investigated. The gas barrier properties of the films have been measured for several gases, namely He, Ne, Ar and O. A variety of techniques have been used to microstructurally characterize the oxide coating. It was found that the barrier layer was uniform, amorphous and free of macro-scale defects. A theoretical model has been proposed that describes the SiO_x layer as a solid with a pore size distribution of 2.7 to 4 angstroms. Using this model, it is possible to account for the gas transmission properties exhibited by the films.