Challenging the Minimum Feature Size Assumptions in Embedded 3D printing

Embedding 3D printing technology enables the creation of intricate and customized components during manufacturing. This is achieved by suspending the printing material in a fluid with yield stress properties, leading to enhanced stability and precision of complex structures. The printed filament's structure is shaped by the fluid's yield stress and the ink material's properties. Despite this, interfacial instabilities hinder the minimum stable feature size, which can be calculated using the plasto-capillary length d~2Γ/ σ, a function of the matrix material's yield stress and the ink-bath interfacial tension. Our research explores rheology's impact on printing resolution by printing silicone elastomer ink (PDMS) in various viscoplastic matrix materials. Our findings showed that we could achieve smaller feature sizes than predicted by the plasto-capillary length, consistent with prior studies. We explain this through the concept of a solid sphere in a yield stress fluid where the effective area changes due to yield stress. We also derived an empirical modification of the plasto-capillary equation for printing Newtonian liquids in yield stress fluid baths. These results provide a way to determine the minimum feature size based on the rheological properties involved more precisely in embedded 3D printing.