Mapping and connecting bulk rheological criteria and microstructure evolution of printable ceramic gels for direct ink writing

Direct Ink Writing (DIW) is an additive manufacturing technique shifting from lab-based research to industrial-scale manufacturing. DIW offers a clear advantage in materials versatility through formulation design of printable yield stress fluids (YSFs). Quantifying and predicting the printability of YSFs for DIW is an enabling factor for industry adoption. However, commonly reported printability criteria are primarily based on material strength , which cannot capture distinctive rheological features linked to printing behaviour. Other criteria such as flowability , recoverability , and stretchability , are emerging but are not yet settled in the field. Another critical factor rarely investigated is the YSF microstructure’s ability to withstand deformation without disruption. In this work, we use rheo-microscopy to directly map microstructure evolution in pH-responsive strontium titanate (STO) emulsion gels subjected to deformations in shear and extension. Rheo-microscopy, gravity-extension rheology, and direct visualisation during DIW reveal a correlation between microstructure, flow instabilities, and printability . Here we demonstrate that complementary bulk rheological measures in shear and extensional flows and microstructure evolution are all key factors to understand and quantify rheological printability criteria in DIW.