(703f) A 3-D Approach to Model Diffusion in Randomly Distributed Nanocomposite

The mass transport properties of a system with impermeable platelets dispersed in a polymer matrix were investigated, through a CFD algorithm, based on finite volume method; the study of small gas particles diffusion has been approached.

Simulations were carried out on 3-D geometries where different shapes of the lamellae were considered, dispersed in both an ordered and random way; different volume fractions Φ and aspect ratios α of the platelets were considered, as well as, in the ordered structures, different values of the flakes spacing σ. In the case of random systems, multiple structures were analyzed for a given set of parameters and the results were treated statistically to obtain reliable information.

The results show that the permeability of the ordered geometries decreases with the product αΦ, and the curves corresponding to different filler shapes have a similar qualitative behavior. It has also reported that the 3-D approach is to be preferred over a simple 2-D one, that overestimates the barrier properties. The data relative to random dispersions also decay with αΦ, but their barrier properties are in general worse than those of ordered dispersions of circular lamellae. The random systems behavior is accurately predicted by the Nielsen's model approach.

The effect of a third phase on the platelets-matrix interface was also investigated to mimic phenomena such as bad adhesion of the organic phase on the filler surface or local crystallization of the polymer. The former situation in particular seems to reduce the barrier effects of the filler in a not negligible way and can compromise the performance of nanocomposite material.