Rheology and Flow Behavior of Concentrated Colloidal Gels for Direct-Write Assembly of 3D Mesoscale Structures

3D mesoscale structures with various patterns have been successfully fabricated by direct-write assembly of concentrated colloidal gels. Geometric fidelity of these structures is very important to functionality as devices and has been closely tied to gels microstructure dynamics, which depends on the rheology and shear history. Here, Al2O3 gels were prepared and employed as model materials. A thixotropic rheological model was developed to show the time dependent behavior of gels structure during shear flow. The model accounts for structure formation and attrition, each with a shear history dependent rate constant. The true wall stress was measured by correcting the end effects and wall slip. The extrusion flow dynamics of the gel was simulated by using CFD method to disclose the structure profiles of extrusion filaments and predict the structure evolution of as-deposited filaments.