Determining Printability of Nanostructured Epoxy/Block Copolymer Blends for Direct Ink Writing

Direct ink writing (DIW) is a versatile, material agnostic additive manufacturing method where the printability of a material is solely dependent on the rheological properties of the inks. We have previously shown that for inks consisting of epoxy/block copolymer (BCP) blends, transient creep testing has proven to be the most effective method to determine the printability of the inks. However, the testing of these nanostructured materials is highly sensitive to the careful selection of the pre-shear conditions used during testing. Poor pre-shear protocols can result in preferential rearrangement of the nanostructures and an inaccurate characterization of the yield stress, and thus the printability, of the materials. In this talk, we will show that large amplitude oscillatory shear is the most effective pre-shear method to obtain repeatable rheological results from the transient creep testing. Through the consistent application of this approach, through the characterized yield stress, we were able to identify the phase boundaries in the epoxy/BCP inks when the BCP micelles undergo an order-order transition from spherical to hexagonal micelles. This work demonstrates the effectiveness of our methodology to determine the yield stress of the nanostructured inks and connect the nanostructure to the printability of the ink, which can be used to facillitate the printability of new inks.