SELF-ASSEMBLED ANISOTROPIC COLLOID SYSTEMS FOR PHOTONIC APPLICATIONS
Stelson, Angela Carrier
Photonic crystals are optical structures periodic on the length scale of light, and support useful attributes including photonic bandgaps (ranges of frequencies forbidden from propagating in the material), negative refraction and slow light effects (extremely low group velocity). Such effects have applications in sensors, waveguides, solid-state lighting, photovoltaics and superlenses, among others. The optical characteristics of a photonic crystal are determined by the interplay of structure, order and materials properties in the crystal. Self-assembled anisotropic colloids are attractive templates for photonic crystals due to their cost effectiveness and diversity of structures and symmetries. Introducing entropic and enthalpic effects to engineer inter-particle interactions increases the variety of phases and mesophases in anisotropic colloidal assemblies. In this dissertation, the photonic properties of self-assembly inspired structures are investigated via electromagnetic simulations. New paradigms for self-assembled photonic crystals are developed, and desirable properties such as photonic bandgaps, negative refraction, and slow light are correlated with structural and materials parameters informed by colloidal assemblies. Specifically, the photonic crystal properties of partial order rotator crystals, Archimedean tilings, and quasi-two dimensional ‘slab’ crystalline structures are investigated. All three systems display large photonic bandgaps. Slow light effects are observed in the rotator crystal and Archimedean tilings. As well, negative refractive index is predicted in the ‘slab’ crystal and the Archimedean tiling. These projects open new frontiers for research to manipulate self-assembled systems for photonics. Additionally, the assembly of colloidal C60 platelets is investigated under two-dimensional confinement and electric field. The C60 platelets are synthesized via a co-solvent precipitation method. The particles assemble under dipolar forces, dielectrophoretic forces, and electrohydrodynamic flows. Frequency-dependent phase transitions occur at the critical Maxwell-Wagner crossover frequency, where the effective polarizability of the particles in the medium is substantially reduced. Structures form as a function of field strength, frequency and confinement including hexagonal, oblique, string fluid, coexistent hexagonal-rhombic, and tetratic.
Materials Science; Colloids; Fullerenes; Negative Refraction; Photonic Bandgaps; Photonic Crystals; Self-assembly
Liddell, Chekesha M.
Giannelis, Emmanuel P.; Clancy, Paulette
Materials Science & Engr
PHD of Materials Science & Engr
Doctor of Philosophy
Attribution 4.0 International
dissertation or thesis