Thin Polymer Films: Simple Optical Determination of Molecular Diffusion Coefficients

The possibility to assess diffusion coefficients of small molecules in packaging polymer films directly on the shelf, or even along the fabrication line, without the use laboratory equipment commonly employed for gravimetric methods would represent a paradigm changer in the evaluation of barrier properties and byproduct formation in goods packaging and device encapsulation. In this work, we demonstrate a simple, effective, and versatile method for the determination of the molecular diffusion coefficients that exploits simple UV–vis spectroscopy and is suitable for any polymer film. This simple method also allows the direct identification of the intercalating molecule without the need for chemical targeting or of complex laboratory equipment. For this purpose, we report on the assessment of diffusion coefficients of both polar and nonpolar molecules including water, ammonia, methanol, ethanol, toluene, and even hexafluorobenzene into polyvinyl chloride wrap commercialized for food packaging.