Modeling Mass Transport Properties in Binary Composite Systems

The description of mass transport properties of low molecular weight species in heterogeneous polymeric systems is of great importance. The theoretical analysis of composite materials behaviors is indeed fundamental for the proper material design of such systems for a variety of different applications. Among the others, immiscible polymer blends as well as block copolymers are often of interest for their ability to combine properties of two or more materials. Semicrystalline polymers are also systems of great industrial importance, which require a two phases modeling in order to describe their behavior. In recent years, the development of nanocomposite materials was employed for barrier applications by incorporating impermeable platelets in the polymer phase. This technology is also suitable for the design of membranes for gas separation, and to this aim, particles selective to one or more gases, such as for instance zeolites or metallic organic frameworks, are dispersed in the polymer phase. All these examples are constituted by two, or more, well defined and well distinguished regions (of different length scale) characterized by their value of gas permeability Pi. The resulting permeability of the complete heterogeneous medium is then related to these Pi values but also to the relative weight of the two phases as well as the system morphology, i.e. the shape of the dispersed phase. The aim of this work is to develop a valuable tool for the description of transport properties in composite media, able to evaluate the permeability as function of system morphology. Numerical calculations are thus employed to model the two-phases system in a wide range of relative fraction of the two components and varying their characteristics. Results are then compared with existent model equations in order to investigate their predictive ability and ranges of validity.