Tunable Elasto-Viscoplastic Properties of Polymer Blends for 3D Printing Applications

Post-extrusion flow dynamics of soft matter are governed by their elasto-viscoplastic (EVP) rheological properties, which influence filament stability, die swelling, and shape fidelity in extrusion-based 3D printing. Achieving precision and control in printed structures requires optimizing yield stress, viscoelasticity, and extrusion pressure to minimize excessive die swelling and material spreading, which can lead to unstable extrusion and poor print fidelity. We investigate Carbopol-polyethylene oxide (PEO) blends as model EVP fluids, systematically varying their composition to assess die swelling, print width, and deposition accuracy. Rheo-SAXS measurements reveal that die swelling can be directly related to characteristic nanoscale lengthscales. Parametric analysis using the Ohnesorge ( $Oh$ ) and modified Bingham ( $\xi /Bi$ ) numbers reveals that at high $\xi /Bi$ (yield stress, Pa) and , surface tension and viscoelastic effects dominate, leading to excessive die swelling and spreading upon deposition (up to 1.6 and 6 times the nozzle diameter, respectively), ultimately causing drop formation rather than stable filament extrusion. Conversely, $Oh\ge {10}^2$ and $\xi /Bi\le 8\times {10}^4$ ensure optimal printability, high shape fidelity, and minimal die swelling. These findings guide EVP formulation and optimal extrusion pressure using dimensionless groups that capture material rheology and flow behavior.