Quantifying hierarchical mixture quality in polymer composite materials: Structure and inhomogeneity in multiple scales

Mixture quality plays a crucial role in the physical properties of multi-component immiscible polymer mixtures including nanocomposites and polymer blends. Such complex mixtures are often characterized by hierarchical internal structures, which have not been accounted for by conventional mixture quantifications. We propose a way to characterize the mixture quality of complex mixtures with hierarchical structures. Starting from a concentration field, which can be typically obtained from TEM/SEM images, the distribution of the coarse-grained concentration is analyzed to obtain the scale-dependent inhomogeneity of a mixture. The hierarchical nature of a mixture is characterized by multiple characteristic scales of the scale-dependent inhomogeneity. We demonstrate how the proposed method works to characterize sizes and distributions in different dispersions. This method is generally applicable to various complex mixtures.