Mechanism study on phase behavior of colloids with depletion attraction

Abstract

This dissertation investigates the mechanism on the phase behavior and self-assembly of colloidal systems under depletion attraction, a suitable model for mimicking and simulating the behavior of atoms and molecules. Colloidal particles offer a more accessible model than real atoms and molecules, as their larger size allows for direct observation. However, existing assembly methods for colloidal particles have limitations, such as complex pretreatment or lack of particle-level control. Depletion attraction can address these issues, enabling controlled self-assembly and rich phase behavior in colloidal systems. The research is divided into three parts. First, the study explores the depletion-mediated phase behavior of polystyrene particles dispersed in water, examining the effects of concentration and salt on fluid, crystal, and glass formation. Generalized phase boundaries are established based on pair potentials, and fluid-crystal and glass formation boundaries are analyzed in terms of potential well depth as well as assembly rate. Second, the scaling laws of dendritic growth in colloidal systems are investigated using depletion interaction in aqueous suspensions of spherical colloids. This approach yields insights into the formation-determinants and growth kinetics of dendrites, revealing that their formation depends on colloidal flux parameterized by an assembly time scale. Lastly, a single-step, bottom-up approach is presented for inducing regioselective crystallization of colloidal particles on patterned substrates. This method involves the depletion-mediated assembly of particles onto the substrate with controlled morphologies, leading to the regioselective nucleation and growth of colloidal crystals and providing a simple and novel alternative to traditional top-down fabrication techniques. The findings from this dissertation contribute to a systematic understanding of rich phase behavior of colloidal particles, with implications for the use of colloidal systems as atomic models. This research also suggests the potential for crystal patterning using site-selective control of crystallization behavior based on the entropy-dependent nature of depletion attraction.