Tailored Gradient Morphologies and Anisotropic Surface Patterns in Polymer Blends

Gradient morphologies and surface patterns can provide a template for smart materials with tailored local properties. Fabricating such structures in a one-step melt-extrusion process will be most beneficial as they usually require several manipulation steps. In this study, gradient morphologies are developed by melt-spinning matrix-dispersed polypropylene/polystyrene blends as a template system and dynamic control of their formation is achieved, which further leads to anisotropic surface patterns. Cross and longitudinal sections and the surface of extruded fibers are evaluated by scanning electron microscopy. Distinct microstructure gradients regarding size and shape of the dispersed phase are formed in the bulk. After dissolving the dispersed phase, ordered (sub)micron channels appear on the surface, which are further refined by hot-drawing. The resulting textures form anisotropic grooves along the fiber axis on the surface, as verified by atomic force microscopy. Capillary theory is applied to elucidate the formation mechanisms of gradient microstructures in polymer blends during processing. It is shown that all these features can be tailor-made by using the extrusion die as a design tool. By transferring the knowledge to suitable polymer blends and processes, the designed gradient and surface structures can find applications, for instance, in materials with adaptive mechanical or interfacial properties.