Hierarchical and Fractal Structuring in Polymer Processing

The potential of structuring thermoplastic polymers by convection only, using a combination of static mixer elements, which easily produce stratified structures with thousands of layers, and the black box concept that serves to elegantly combine materials in standard co-extrusion technology is investigated. The aim is to obtain an alternative for routes that try to structure organic matter such as polymers down to submicrometer levels, usually via self-organization based on phase separation. Structure is characterized by its complexity, here defined by the level of hierarchy. Horizontal stratification, parallel to the surface, is level 0. Vertical stratification connected to horizontal surface layers, is level 1. A series of horizontal stratifications in distinct places vertically connected to the surface layers is level 2. Higher levels of hierarchy finally result in dendritic structures that are fractal. Applications of complex structures with a huge interface and guaranteed cocontinuity throughout the whole cross section of the products are found in, for example, membranes for fuel cells and gas separators, and in miniaturizing electronic and optical devices such as photovoltaic cells.