MD simulation and cluster analyses of the gas permeability of parylene AF4 membranes

In poly-p-xylylene (parylene) AF4 membranes, amorphous and crystalline areas were constructed by a novel computational technique: a combination of NVT + NPT-molecular dynamics (MD) and “gradually reduce the size” (GRS) methods. The corresponding free volume was determined via the homology cluster method. Crystalline parylene AF4 membranes were found to provide less free volume for the adsorption and transfer of gases than amorphous parylene AF4. The permeability results showed that amorphous and crystalline parylene AF4 membranes have different permeation properties, and the corresponding permeability coefficients approach those observed experimentally. This work determined the behaviours and directions of diffusing gases via a cluster analysis technique. Gas diffusion occurs only along the y-axis in the crystalline area and randomly in the amorphous area. The relative permeability was close to the experimental value.