Gas diffusion in polymer nanocomposites: Role of defects and caves in fillers

Gas barrier in polymers is able to be effectively enhanced by adding air-impervious nano-fillers. It is inevitable that there are some defects or caves on the surface of nano-fillers, which can have a certain effect on the gas barrier. The effect of defects and caves in nano-fillers was investigated using the finite element model in order to better understand the diffusion process in a polymer nanocomposite film with staggered array nano-fillers by varying the microstructural features such as volume fraction, aspect ratio, gaps between fillers, and so on. The results showed that the effect of defects and caves on relative diffusivity arises from the following two aspects: the first is the effect of cave volume which dominates, and the second is the induced effect from defects and caves. A theoretical model for predicting relative diffusivity was developed based on the volume effect, and then was generalized into three dimensions. In order to estimate the value range of the model, the upper and lower boundaries of the model have been derived. Comparisons were then made between the estimated and simulated values, and the results showed that the upper and lower boundaries are basically correct, and especially the upper boundary is on the same order of magnitude as the real value.