Optical microscopy measurements of kT-scale depletion and electric field mediated colloidal potentials, assembly, and landscapes

The ordering of colloidal components is a complex process involving many interactions. Colloidal assembly methods on the kT-scale are the only means of achieving reversible assembly for the removal of structural defects. The ability to assemble colloidal particles into ordered microstructures in a robust manner could serve as a basis for synthesizing meta-materials. The development of such materials has been limited due to a lack of understanding regarding concentrated colloidal interactions in the presence of different potentials and external fields. Consequently, there is an increased desire to generate stochastic models that quantitatively connect interactions governing colloidal ordering to microstructures. In this dissertation, equilibrium and non-equilibrium particle configurations resulting from kT-scale depletion attraction or inhomogeneous AC electric field mediated colloidal self-assembly are directly quantified using interaction potentials and landscape models.;Total Internal Reflection Microscopy (TIRM) and video microscopy (VM) are utilized to directly measure depletion attraction in quasi-2D ensembles of micron-sized colloidal particles. The majority of studies involving depletion interactions currently show depletion potentials that deviate from that of the traditional Asakura-Oosawa (AO) model. More rigorous models have been developed, but these are typically material specific, theoretically complex, and require other intricate computations. We have formulated an analytically simple modified AO potential and demonstrate that it accurately describes directly measured depletion attraction and colloidal phase behavior in a variety of material systems.;Potentials in colloidal systems interacting with inhomogeneous AC electric fields have already been well characterized and linked to equilibrium phase behavior. This work aims to further connect these interactions to the temporal evolution of microstructures that arise during electric field mediated assembly. The particle configurations observed in going from disordered fluids to ordered crystals are captured using order parameters and understood by constructing free energy and diffusivity landscapes based on these order parameters. The effects of system size on the thermodynamics and kinetics of electric field mediated assembly are also considered. The information obtained from this work not only serves to provide a better comprehension of colloidal crystallization dynamics, but it also lays the foundation for developing stochastic models that could be used to optimize controlled colloidal assembly.