Phoretic Transport Of Colloidal Particles In Complex Microenvironments

Abstract

The transport of colloidal particles is often governed by multiple factors. For instance, the localmicroenvironments, such as the geometry of the surroundings, the neighboring chemical species, and associated forces can contribute to the transport of nanoparticles (NPs). NPs migration in biological hydrogels is often hindered by the strong confinement of the media, thus limiting important applications such as drug delivery and disinfection. In this thesis, we explore phoretic transport of colloidal influenced by its local microenvironments. In the first part of the thesis, we demonstrate enhanced NP transport in collagen hydrogels enabled by diffusiophoresis. Contrary to common expectations for boundary confinement effects, we observe a non-monotonic behavior in which maximum diffusiophoretic mobility is observed at an intermediate confinement. We find that such behavior is a consequence of the interplay between multiple sizedependent effects. Our results display the potential utility of diffusiophoresis for enhanced drug delivery. In the second part of the thesis, we study particle transport driven by electroosmosis on a non-uniformly charged surface. Non-uniform electroosmotic flows can often induce complex flow behaviors, which can be used in applications such as enhanced mixing and designing micromotors. We demonstrate non-uniform electroosmosis induced by electrochemical reactions. The non-uniform electroosmotic flow creates multiple vortices, which promote local particle accumulation that subsequently leads to the formation of a colloidal band. The rapid formation of the particle band can be potentially useful for particle separation and preconcentration processes. For instance, we demonstrate these vortices can promote the accumulation of soft colloids such as oil droplets and fat globules. These two studies highlight the importance of local environments to the transport of colloidal particles in which some unique features may arise with the presence of porous media and pH gradient.