Effect of Block Copolymers on the Printability of Epoxy Inks for Direct Ink Writing

Direct ink writing (DIW) is a highly versatile additive manufacturing technique that is applicable for a wide range of materials. The primary determination of the printability is based on the materials rheological properties. However, for nanostructured inks, the rheological characterization can be quite complex. Our work has shown that characterization of block copolymer (BCP) containing epoxy inks show no obvious difference in their rheological properties using traditional oscillatory amplitude sweeps as a function of the BCP concentration. However, significant differences are observed during printing. Instead, transient creep testing is used to show that the BCP containing inks had a lower apparent yield stress and a lower time-dependent decrease in the shear rate as compared to the base epoxy ink, which correlate well will with the printing results The creep testing also can be used to identify the time-dependent behavior of these inks, and identify pressures in which the inks will “clog” during printing, even if they initially print well. This work shows that the nanostructure of printable inks can result in complex rheological behavior, but we have identified transient creep testing as an effective way to characterize the printability of these nanostructured inks.