SiOx gas barrier coatings on polymer substrates: Morphology and gas transport considerations

Plasma-enhanced chemical vapor deposition (PECVD) of SiOx thin coatings on polymer surfaces yields tough hybrid materials with the gas barrier propert ies and transparency of glass. Combination of these properties makes these materials ideally suited for food packaging and biomedical device applicati ons. In this study, we employ a Non-Parametric Response Surface Methods opt imization to identify the Magnetron-PECVD conditions responsible for superl ative SiOx, barrier coatings on poly(ethylene terephthalate) (PET). Oxygen and water vapor permeances of optimized PET/SiOx, composites produced by he xamethyldisiloxane and trimethylsilane have been measured as functions of t emperature and are found to exhibit Arrhenius behavior. The thermal activat ion energy for water val,or permeation, unlike that for oxygen permeation, depends on barrier performance and increases by as much as 20 kJ/mol with a n increase in barrier efficacy. Examination of these materials by phase-ima ging atomic force microscopy and energy-filtered transmission electron micr oscopy reveals a correlation between SiOx, morphology (including defects) a nd barrier performance. Morphological and permeation results are compared t o identify some of the physical factors governing water vapor permeation th rough SiOx-modified polymers.