Polymer materials are rarely used in their pure in applications. They are often filled with additives that improve their processability and mechanical or electrical properties. An understanding of the polymer-filler interaction and the ramifications for the properties of filled polymer blends is a matter of significant practical interest. Phase separation plays an important role in determining the morphology and properties of filled polymer composites, which usually are a blend of various macromolecular fluids, and additive particles. Despite the wide application of these blends, the development and the stability of the phase separating morphology are not fully understand. In particular, the interference of the filler induced composition waves remains unexplored. Mesoscale structures such as particle clusters have been observed both experimentally and in numerical computer simulations of circulating fluidized beds. In numerical simulations, these structures result from nonlinearities present in even the simplest of two-fluid models based on closure models that account only for phase interactions at the scale of the particles. Simple particle-fluid drag closure models are one example. In many cases, the mesoscale structures have been demonstrated to have predominant effects on the macroscopic behavior of fluidized beds. As a result, some two-phase flows can be computed using very simple two-phase flow averaged conservation equations as long as enough resolution is used.
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