Permeability in barrier membranes: Comparison between experiments, direct calculations, and analytical models

This paper compares direct calculations, experimental data and analytical models in materials with controlled barrier microstructure. Confocal Raman was used to follow mass transport of a penetrant, hexadecanol (HDOL), through the barrier structure. produced by carving holes in specific positions and orientations in a polydimethylsiloxane (PDMS) matrix. Finite element method (FEM) was used to predict maps of HDOL concentration around the obstacles, which were directly compared to Raman data. Effective diffusion coefficients were obtained in homogeneized microstructures of slender obstacles in diluted and semi-concentrated obstacles regimes. Results were compared with predictions of simple analytical models: Nielsen, Lape, those derived from the ideas of Bharadwaj (Greco; Greco and Maffezzolli), and those developed from FEM simulations (Minelli et al. and Dondero et al.). For the first time, predictions of these widely used analytical models could be tested against well-controlled barrier membranes. The influence of obstacle orientation, size polydispersity and eventual aggregation, all features occurring in real polymeric nanocomposites are analyzed. Some limitations about the use of simple analytical models to interpret permeability data in real nanocomposites are discussed.