The Role of Shear and Extensional Flows in 3DP-Induced Alignment of Block Copolymer Nanostructures*

Biological systems frequently achieve remarkable functional material properties through self-assembly of complex, hierarchically ordered structures. We have previously demonstrated controlled alignment of block copolymer (SEBS) nanostructures by leveraging the flows intrinsic to melt-extrusion 3D printing. These processing flows align the stiff cylindrical polystyrene domains within the rubbery matrix to achieve nearly two orders of magnitude of mechanical anisotropy parallel versus perpendicular to the print path. Here, we investigated the relationship between the local shear and extensional flow history and the resulting material nanostructure and extent of alignment. To accomplish this, we employed high spatial resolution imaging techniques to capture the spatial heterogeneity in structure induced by the non-uniform flow profile of 3D printing. Our outcomes help inform the rational design of 3DP nozzles and flow conditions to improve control over material anisotropy in 3D printed nanostructured polymers.