Photonic crystals fabricated by block copolymerization-induced microphase separation

Motokawa, Ryuhei   

Block copolymers (BCPs), which spontaneously form periodic nanostructure by microphase separation, have attracted attention as materials for three-dimensional photonic crystals (3D-PCs). However, in conventional solution casting method, the molecular weights of BCPs for PCs are so large that structural relaxation on the microphase separation cannot be completed due to strong chain entanglements. Therefore, 3D-PC for visible wavelength has not been reported, whereas one-dimensional lamellar PCs for visible and near-infrared lights were fabricated using grafted and swollen BCPs. Here we overcome the difficulty by block-copolymerization-induced microphase separation. This method induces the microphase separation when molecular weights of the BCPs are small enough for the structural relaxation, and then enlarges the microphase-separated structure up to optical wavelength while maintaining the self-similarity. Our 3D-PCs have the reflection wavelength (Lm) up to 1000 nm with full width at half-maximum of 0.05Lm.