Yield Stress Dependence on the Nanostructure of 3D Printable Epoxy/Block Copolymer Inks using Rheological Creep Testing*

Rheological characterization is critical in determining the printability of materials using direct ink writing (DIW). Our previous work showed that the results from transient creep testing correlated better to the printability of the DIW inks than results from traditional oscillatory amplitude sweeps. Creep testing was used to show that epoxy/block copolymer (BCP) inks had time-dependent flow properties resulting in the identification of critical apparent yield stress for the materials on time scales relevant to printing. In this presentation, we will build on this previous work to show the effects of the ink composition and the resultant BCP nanostructure on the yield stress of these materials. Specifically, the transition from spherical nanostructures to cylindrical structures results in three-fold increase in the yield stress. Additionally, we will demonstrate the importance of carefully selecting the preshear conditions to get repeatable results on these nanostructured epoxy/BCP inks.