Micrometric Monodisperse Solid Foams as Complete Photonic Bandgap Materials.

Solid foams with micrometric pores are used in different fields (filtering, 3D cell culture, etc.) but today, controlling the foam geometry at the pore level, their internal structure, the monodispersity along with their mechanical properties is still a challenge. Existing attempts to create such foams suffer either from slow speed or size limitations (above 80 µm). In this work, by using a temperature-regulated microfluidic process, 3D solid foams with highly monodisperse open pores (PDI lower than 5%), with sizes ranging from 5 to 400 µm, and stiffnesses spanning two orders of magnitude are created for the first time. These features open the way for exciting applications, in cell culture, filtering, optics, etc. Here, the focus is set on photonics. Numerically, these foams are shown to open a 3D complete photonic bandgap, with a critical index of 2.80, thus compatible with the use of rutile TiO2. In the field of photonics, such structures represent the first physically realizable self-assembled FCC (Face-Centered Cubic) structure that possesses this functionality.