| The goal of this dissertation is to develop new colloidal particles that are capable of forming reversible, directional bonds with specific well-defined symmetries. Due to their size, anisotropic colloids are particularly promising for photonic applications, where tetrahedrally-interacting colloids are expected to assemble into a material with a complete band-gap in the visible. However, until now there has yet to be introduced a systematic method of producing monodisperse colloids and assembling them with directional, reversible interactions. Here we show the fabrication and directed assembly of "patchy particles," a set of colloidal molecules comprising an almost-spherical anti-patch and chemically distinct patches with strictly defined symmetry, number and size, located on the particle surface. By maintaining separate functionalizable chemistries on the two types of surfaces, assembly is shown to occur at the patch both by charge screening and by biotin/Neutravidin linkages. We also introduce temperature-induced reversibility to the directed assembly by incorporating ssDNA on the patches. We demonstrate the technique by forming daisy chains from patchy 'dimers,' particles with two diametrically-opposed patches. We also observe branched chains upon the addition of a small number of higher-order patchy particles. Finally, we fabricate particles with one type of DNA on the patches and another on the anti-patch for use in self-replicating systems of colloids. Our results confirm that anisotropic colloidal molecules may be engineered in a highly reproducible fashion on the bench top and manipulated in water or organic solvent to induce reversible, directed assembly. |
