Morphology and gas barrier properties of thin SiO_xcoatings on polycarbonate: Correlations with plasma-enhanced chemical vapor deposition conditions

Plasma-enhanced chemical vapor deposition of SiO_x coatings on thermoplastics provides a viable route for production of transparent composite materials with high fracture toughness and high gas barrier properties, which are important considerations in the food packaging and biomedical device industries. By examining several series of systematically varied SiO_x/polycarbonate composites, we have identified design correlations between coating characteristics (thickness, density, surface roughness, and O₂ transmission) and deposition conditions (time, power, pressure, and flow rates). Of particular interest is the observation that the thermal activation energy for O₂ permeation through these composites increases (by up to 17 kJ/mol) as their barrier efficacy increases.