Date

2015

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Chemical Engineering

First Adviser

Mittal, Jeetain

Abstract

Colloidal particles exhibit versatile dynamic behaviors and structures, dependent on various interactions between these particles. In this dissertation, we studied two representative colloidal systems: one with classic repulsive interparticle interactions and the other with novel DNA-mediated interparticle interactions.In the first part of this dissertation, we studied the equilibrium and nonequilibrium dynamics and structure of soft particles, which are modeled by the inverse power potential. The freezing-point scaling relation, to a good approximation, collapses diffusivity and viscosity data of different particle softness.Using the freezing-point scaling relation as a starting point, shear rheology and microstructures of particles with different softness are studied. A universal shear-thinning behavior was observed for particles with different softness in absence of hydrodynamics, albeit softer particles exhibit stronger shear-thinning tendency. By investigating the microstructure of these systems, a strong relation between the changes of the structures and the particle softness was found in presence of shear. These different microstructure changes in responses to the shearing might explain the extent of shear-thinning behavior for different particle softness.In the second part of this dissertation, we studied the self-assembly of DNA-functionalized particles (DFPs). The coarse-grained model was developed for DFPs. The potential of mean forces (PMFs) between two DFPs were computed as a function of temperatures, DNA grafting density and lengths of the hybridizing and non-hybridizing parts of DNA. The computed PMFs were used to study the self-assembly of ordered 2D binary crystal lattices. Three crystal phases were identified: square lattice, alternating-string (A-S) hexagonal lattice, honeycomb lattice, by controlling the binding energies between different particle species. The square lattices always exhibit perfect compositional ordering while significant defects appear in hexagonal lattices due to the interplay between thermodynamic and kinetic factors.

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