Date of Completion

8-29-2014

Embargo Period

8-26-2024

Major Advisor

Tai-Hsi Fan

Associate Advisor

Nejat Olgac

Associate Advisor

Devendra Kalonia

Associate Advisor

Tianfeng Lu

Associate Advisor

Anson Ma

Field of Study

Mechanical Engineering

Degree

Doctor of Philosophy

Open Access

Campus Access

Abstract

Predicting transport properties and hydrodynamic interactions of colloidal particles in complex or polymer fluids is important for many applications including manufacturing and storage of food and pharmaceutical products. One of the interesting behaviors in colloid-polymer mixtures is the so called macromolecular crowding effect, that is, the self and mutual diffusivity or association of the nanoparticles are strongly influenced by the surrounding polymer chains as the crowding agents. Depending on the colloid-polymer interactions, the polymer chains can be adsorbed to or depleted from the colloidal surface. This thesis addresses the depletion phenomena. At submicron scale, both colloidal particles and polymer chains are strongly influenced by thermal fluctuation in aqueous solutions. Polymers constantly sample their configurations in the solution. Appearance of a surface inhibits certain configurations to be sampled by polymers. This is essentially due to the volume exclusion effect down to the monomer level. To avoid the loss of configuration entropy, polymers tend to be away from the colloidal surface, and thus form a depletion zone around the colloids, which also changes the particle's mobility. What is more interesting is the attractive interaction potential generated between nearby colloids due to the unbalanced entropy or osmotic force when two depletion zones overlap. This often leads to phase separation in the bulk, and therefore the polymer depletants can be used to tune the phase behaviors of colloid-polymer mixtures. The thesis focuses on microscopic dynamics and investigates the stochastic and correlated motion of pair and many particles in nonadsorbing polymer solutions.

On the fluid flow aspect, a three-dimensional boundary integral model has been developed to compute the pair additive mobility tensor of colloids. It is found that the presence of depletion layers enhances the mobility of the particles for the decomposed relative and common motions along parallel and perpendicular directions. The enhancement is even stronger when colloids have relative motion toward each other. The hydrodynamic resistance is connected to the thermal fluctuation through the fluctuation-dissipation theory, so that the Brownian random force applied to the colloids can be realized in the long-time or diffusive regime. The effect of depletants on the auto- and cross-correlation of pair interactions are investigated in details.

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