The effect of shape and orientation on the barrier properties of flake-filled composites: A 3D approach

Abstract

We carry out fully three-dimensional (3D) simulations in flake-filled composites with the objective of determining the effect of flake shape and orientation on their barrier properties. Our simulations are carried out in multi-particle unit cells, each containing up to 4,000 individual flakes. We represent the flakes as 2D rectangles of dimensions (l) and (w); this representation is suitable for very thin flakes, such as exfoliated nano-platelets of montmorillonite or graphene-oxide. We analyze the effect of flake shape on the effective diffusivity Deff and find that square flakes offer the best barrier improvement. For constant flake area, the barrier properties are predicted to decrease as the diagonal and/or the aspect ratio of the flake increase. We also analyze the effect of flake misalignment with respect to the direction of macroscopic diffusion and find that, in a manner similar to what has been seen in 2D systems, the decrease in Deff with flake loading and/or flake diameter is less severe as the degree of misalignment increases. Finally, fully 3D systems are compared to systems in which one flake dimension is progressively approaching the dimensions of the unit cell, thus rendering mass transport essentially two-dimensional. We find that in this case the predicted Deff is lower than that of a system in which mass transfer is three-dimensional in nature. Copyright 2019. Used by the Society of the Advancement of Material and Process Engineering with permission.