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Abstract

Suspensions are mixtures of solid particles in a fluid. If a suspension is dilute, the particles merely elevate the Newtonian viscosity. For dense suspensions, however, staggering and sometimes catastrophic effects can be observed, such as discontinuous shear thickening (DST) and shear jamming (SJ). In DST, the suspension viscosity jumps discontinuously, often by orders of magnitude, at a critical shear rate. In SJ, the viscosity can fully diverge under shear, leading to reversible, shear-induced solidification. These behaviors arise from particles being pushed into direct contact by shear, at which point they interact frictionally. This can form a particle network that provides solid-like qualities. However, phenomenological models did not clearly explain why aqueous cornstarch suspensions demonstrate this behavior while seemingly similar systems do not. In this thesis, we show that what differentiates aqueous cornstarch suspensions is the capacity to form interparticle hydrogen bonds. This elevates the interparticle friction and provides rigidity to the particle network. Armed with this knowledge, we demonstrate that other systems can easily be designed to display strong DST and SJ, provided one pays close attention to the chemistry of the solvated particle-particle interface. Extending these findings, we explore a unique repercussion of how hydrogen bonding elevates interparticle friction: adhesive interactions. Adhesion can be clearly observed in SJ systems, and works to increase friction. So far, adhesion has been neglected in simulations and its incorporation will likely aid in the quantitative agreement between simulations and experiments. Finally, we apply these findings to design a novel system with enhanced DST and SJ at reduced particle concentration. We show that concentrations necessary for DST and SJ are sensitively dependent on particle aspect ratio, which can be a valuable tool in tuning DST and SJ behavior for dynamically responsive material applications. Overall, this work integrates the chemical perspective of solvated solid interfaces with granular and soft matter physics. In this way we provide a framework to anticipate and prevent unwanted flow behaviors in processing applications, and contribute design recommendations for how to engineer DST and SJ for dynamically-responsive materials.

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