Browsing by Subject "colloidal gels"
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Item Rheology and Flow Behavior of Concentrated Colloidal Gels for Direct-Write Assembly of 3D Mesoscale Structures(University of Texas at Austin, 2010-09-23) Zhu, Cheng; Smay, James E.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.Item Structure and phase behavior of polymer-linked colloidal gels(AIP Publishing, 2019-08-29) Howard, Michael P.; Jadrich, Ryan B.; Lindquist, Beth A.; Khabaz, Fardin; Bonnecaze, Roger T.; Milliron, Delia J.; Truskett, Thomas M.Low-density “equilibrium” gels that consist of a percolated, kinetically arrested network of colloidal particles and are resilient to aging can be fabricated by restricting the number of effective bonds that form between the colloids. Valence-restricted patchy particles have long served as one archetypal example of such materials, but equilibrium gels can also be realized through a synthetically simpler and scalable strategy that introduces a secondary linker, such as a small ditopic molecule, to mediate the bonds between the colloids. Here, we consider the case where the ditopic linker molecules are low-molecular-weight polymers and demonstrate using a model colloid–polymer mixture how macroscopic properties such as the phase behavior as well as the microstructure of the gel can be designed through the polymer molecular weight and concentration. The low-density window for equilibrium gel formation is favorably expanded using longer linkers while necessarily increasing the spacing between all colloids. However, we show that blends of linkers with different sizes enable wider variation in microstructure for a given target phase behavior. Our computational study suggests a robust and tunable strategy for the experimental realization of equilibrium colloidal gels.