Solvent‐Rich Pre‐Coagulation Bath for Tunable Liquid‐State Fusion Enables Robust Two‐Step Polymer Embedded Printing

Abstract Effective interlayer fusion is a critical step enabling a 3D printing process. For engineering polymer printing, interlayer fusion is usually either heat‐enabled or binder‐based, which may introduce thermal residual stress, warpage, and undesirable impurities. To overcome such challenges, a two‐step immersion phase separation (IPS)‐based room‐temperature polymer fusion and solidification approach for self‐supported engineering polymer printing, termed IPS‐embedded 3D printing (IPS‐E3DP) is introduced. IPS‐E3DP is implemented by first depositing polymer inks in a solvent‐rich yield‐stress pre‐coagulation support bath to have an intermediate green part and then immersing the intermediate green part in a non‐solvent coagulation bath for complete solidification. During the first critical step, dissolved polymer ink holds its deposited shape and fuses with a previously deposited polymeric feature in the pre‐coagulation support bath. Specifically, it is the high‐concentration solvent bath (usually 80% or higher) that enables tunable liquid‐state fusion of polymers when the deposited polymer solidifies, and it is the yield‐stress support bath that prevents the deposited polymer ink from spreading and deformation during fusion. IPS‐E3DP enables the self‐supported room‐temperature high‐fidelity printing of a wide range of engineering polymers, blends, and composites with superior geometric complexity. The process can be tailored as a polymer binder‐based printing approach for versatile material printing.