Sol-Gel Chemistry of Inverse Opals

Controlling nano to microscale structuration enables one to alter a material’s optical, wetting, mechanical, and chemical properties. Structuration on this scale can be formed from spherical building blocks; in particular, monodisperse, spherical colloids assemble into crystals that can be used to template an ordered, porous structure known as an inverse opal. The structure’s porosity and periodicity provide control over both light (photonic effects) and fluid flow (wetting effects). Controlling the composition allows chemical functionality to be added to the ordered, porous structure. Inverse opals are widely used in many applications that take advantage of these properties, including optical, wetting, sensing, catalytic, and electrode applications; however, high quality structures are necessary to maintain consistent properties. Many of their properties stem from the structure itself, so controlling inverse opals’ structure (including the local composition) provides the ability to control their properties, with the potential to improve some applications and potentially enable additional ones. This thesis explores how molecular precursors can be used to control colloidal assembly and therefore alter the optical and wetting properties of high quality inverse opals. Using a bio-inspired approach, highly ordered, crack-free, silica inverse opals can be grown by co-assembling the colloidal template with a sol-gel matrix precursor using evaporation-induced self-assembly. Using sol-gel chemistry, the size, shape, and charge of the precursor can be controlled, which can be used to tune the colloidal assembly process. Here, we use the sol-gel chemistry of the precursors to control both the morphology and composition of these photonic structures. In particular, temperature-induced condensation of the silica sol-gel matrix alters the shape of an inverse opal’s pores (Chapter 2), and silica and titania precursors can be mixed to make hybrid oxide structures (Chapter 3). Additionally, rationally designed precursors enable the fabrication of crack-free inverse opals in materials beyond silica, which we show for titania as a proof-of-concept (Chapter 4). By controlling the structure and composition with sol-gel chemistry, we can tailor both the optical and wetting properties, as discussed in the second part of each chapter; these properties have important effects for the various applications. In this way, sol-gel chemistry can be used to assemble inverse opals with com