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Interfacial Interactions and Dynamic Adhesion of Synthetic and Living Colloids in Flow

Abstract
This thesis focuses on the interactions between flowing particles and a surface, where hydrodynamics couples with chemical interactions in order to modify the way they come into play. First this thesis shows how electrostatic chemical heterogeneities on a flowing particle affect the interactions with a wall, using a highly tunable electrostatically heterogenous system produced by adsorbing small amounts of cationic polyelectrolytes onto silica particles in suspension and studying their behavior in flow over the fixed surface. By comparing this behavior to a system with equivalent chemical heterogeneity on a channel wall it was shown that the rotation of a particle will produce a lower attempt frequency, resulting in chemical heterogeneity being less effective on a flowing particle then on a fixed surface. This establishes the importance of hydrodynamics in the chemical interactions of flowing colloids. Next this work shows how swimming of Escherichia coli increases both the frequency of bacteria encountering a surface and the durations of the resulting engagements, in an unconfined flowing environment, due to hydrodynamic interactions between bacteria and surfaces. This swimming effect was decoupled from the effect of flagella interactions. It was found that the presence of flagella, when not active, producing steric kicks, increasing the escape frequency and as a result reducing surface engagements length. Expansion of this work showed that the effects caused by morphological differences between bacteria strains can be significantly reduced by altering the mechanical properties of a surface coating. Finally, this thesis shows that rod shaped particles are able to diffuse through a concentration boundary layer and adhere to surfaces at a rate faster than possible with spherical particles, due to hydrodynamic interactions between the non-spherical particles and the surrounding fluid. Current literature contains a wide variety of experiential results and mathematical predictions for the behavior of rods in flow but the lack of consistent systems with well-studied spherical controls has led to many discrepancies in their results. This thesis addresses these apparent discrepancies using model rod-shaped silica particle suspensions and spherical controls. Overall, this thesis probes the effects of three hydrodynamic effects on interactions between particles and surfaces in the presence of flow.
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