Particulate flows and heteroaggregation studied by optical imaging and fluorescence spectroscopy

The production of multiscale heteroaggregates of microparticles coated with nanoparticles has generated renewed interest in recent literature due to the wide-ranging applications of such structured particles. These applications include particle stabilization, nanotemplating, and drug delivery, among others. In the past, the majority of heteroaggregation studies and associated applications have involved rigid, spherical particles. However, as part of a multiscale heteroaggregate, hydrophilic hydrogel particles can be used to open a whole range of new applications. These hydrogel particles have also been of great interest recently due to their significant microencapsulation capabilities and variety of delivery mechanisms. This dissertation is focused on gaining understanding of the heteroaggregation of hydrogel microparticles and nanoparticles and of particulate flows that could potentially be used to influence aggregate formation.;First, concentrated noncolloidal particle suspensions undergoing oscillatory torsional flow between parallel plates were studied using optical imaging. Much of the work focuses on the effect of moderate strain amplitude and frequency on particle migration. Also explored were various effects that can lead to enhanced or reduced particle migration in the flow.;Next, a new quantitative application of fluorescence spectroscopy was developed in order to study the interaction of oppositely charged hydrogel microparticles and nanoparticles in suspensions. Optical microscopy was first used to determine the type of aggregate morphology formed by mixtures of alginate microparticles and fluorescently tagged chitosan nanoparticles at different concentration levels. It was hypothesized that due to fluorophore and particle interaction properties that fluorescence spectroscopy would be able to quantify the boundaries between different types of interactions in the system. With this new technique, the effect of the concentration ratio of nanoparticles to microparticles and the total overall particle concentration was also explored.;Finally, after developing the application of fluorescence spectroscopy for quantifying particle interaction, varying the pH of the interaction environment where heteroaggregation occurs was studied. pH is an important parameter in hydrogel microcapsule and nanocapsule delivery and in heteroaggregation behavior. The change in interaction behavior of alginate and chitosan particles was explored and the capabilities and limits of fluorescence spectroscopy were determined.