The astonishing variety of functionalities found in nature is almost always based on a self-assembly of relatively simple building blocks over multiple length scales, typical in hierarchical arrangements. This concept continues to inspire scientists that seek possibilities to create functional materials in a cheap, fast and simple way. Colloidal particles are interesting in that respect as they can be synthesized with high uniformity and precision to yield building blocks with nanoscale dimensions. In the simplest case, such particles are of spherical shape and do not have any special properties by themselves. However, their uniform size allows such spheres to assemble into ordered crystals, much like oranges or apples on display in a supermarket. In my presentation, I will introduce techniques to assemble such colloidal crystals over macroscopic areas in two- and three dimensions and discuss strategies on how to improve order and homogeneity of these structures. I will then highlight how such colloidal assemblies can serve as masks or templates to create defined surface nanostructures. Translating of the assembly process into the confining element of an emulsion droplet gives rise to supraparticles with a well-ordered internal structure, which are useful components to create hierarchical structuration.
I will introduce how functional, macroscopic properties can emerge from the ordered arrangement of these simple colloidal building blocks, using two examples of the natural world. Structural coloration, responsible for the flamboyant optical effects in many different animals, emerges from the self-assembled colloidal crystals as light waves impinging on the assembly constructively interfere in the visible range. Non-wetting and liquid-repellent surfaces, mimicking the Lotus leaf or the pitcher plant, can be created by controlling the surface topography and surface chemistry. The combination of these two effects can be used to provide simple sensor platforms that distinguish different liquids by their different wettability colorimetrically.