Capillarity-driven interfacial self-Assembly of amphiphilic photonic tiles

Abstract

Photonic crystals adopt periodic nanostructures where the constructive interference of incident light effectively excludes a certain wavelength within the structures. Plants and algae make use of the structures on the epidermis either to protect themselves from detrimental rays or diffract light for a higher photosynthetic efficiency. Photonic surface formed on water constructs photo-protective environment as the epidermal structures protect inner cells. Here, photonic tiles with periodic air cavities are physically etched along with chemical functionalization so that one side of each tile becomes almost superhydrophobic according to Cassie-Baxter model. The amphiphilicity facilitates the assembly of photonic tiles at the air-water interface in that the interaction force of etched tiles at the air-water interface becomes stronger than that of plain tiles. In addition, the amphiphilic tiles rarely stand up in water, which is crucial for a uniform assembly. The assembly of photonic tiles can cover two- and three dimensional water interface, which makes a liquid photonic mirror and a new type of photonic ball, respectively. The assembly at the air-water interface can be transferred to a solid substrate to make photonic surfaces that have own properties of the substrate. These liquid or solid photonic surfaces can create photo-protective reservoir for cells or algae or light harvesting membrane in solar cells.