(534b) Thixotropy-Guided Design of Printable Gels

Soft materials exhibit a complex interplay between structure, dynamics, and rheological behavior, presenting significant challenges in accurately predicting their response to shear stress. In this study, we investigated the properties of thixotropic yield stress fluids, which are a class of materials that exhibit properties intermediate between fluids and solids due to the self-assembly of nanostructures. When these materials are subjected to stress, their nanostructures break down and the viscoelasticity of the fluid decreases. To precisely study these materials, we developed a protocol called serial creep divergence that fully characterizes the time-dependent evolution of material structure and properties. This protocol allows us to quantify the yield stress in this class of soft materials unambiguously. By using this method, we investigated how different types of colloidal bonds affect the mechanical properties of gels, including linear and nonlinear rheology. We find that gels exhibiting thixotropic hysteresis could fully recover their yield stress over time, while non-thixotropic gels possess time-independent yielding metrics. We hypothesize that these time-dependent properties can form the basis of new printability metrics for direct-ink writing applications. To test this hypothesis, we investigate ability of printed filaments to span gaps and the slumping of printed cones under different shear rate conditions. By linking these printing properties to the restructuring kinetics of the material, we aim to create a clear connection between the flow properties of the gels and their printability. This connection will provide practical guidelines for designing printable soft materials and improving their performance in additive manufacturing.