Directionally solidified eutectics exhibit important mechanical, and for emerging systems, interesting magnetic and optical properties. The goal of this work is to understand and apply directional solidification of anisotropic eutectics to form structures with structural motifs, which behave as optical metamaterials. The eutectic’s unique two-phase repeating structures can be controlled by adjusting thermal gradients and cooling rates to finely tune the structure and shape, producing distinctive optical properties with potential for new applications in photonics. This work investigates a eutectic with a eutectic phase that forms facets due to the anisotropy of one of the phases, which restricts the solidification in certain directions. If the solidification direction and facet directions are aligned, the eutectic will uniformly solidify along the thermal gradient. Due to the faceted nature of anisotropic phase, once the eutectic is uniformly directionally solidified the interfaces will be anatomically smooth, providing great benefits to the optical responses.
The microstructures necessary to provide the desired properties may require more complexity than eutectics naturally provide. We and others have observed that a template can be used to guide the phase separation into unique structural motifs. However, it remains experimentally challenging to study the effects of confinement in traditional metallic and ceramic systems. One possible solution is to study the microstructure development in low temperature, optically transparent organic eutectics. In our experiments, organic eutectics were solidified through an assortment of 2D and 3D templates ranging in size and shape. The effects of the templates can be seen in optical images and videos. These effects also were modeled using phase field methods, starting with 2D models of lamellar eutectic solidification through confining geometries. These results were compared to the experimental data.