Thermal property of photonic crystals (PCs) prepared by solvent annealing self-assembly of bottlebrush PS-b-PtBA

One-dimensional photonic crystals (1D PCs) prepared by solvent annealing self-assembly of bottlebrush block copolymers have attracted much attention due to their low cost and convenient preparation. However, such 1D PCs are usually unstable as the reflectance will red shift at high temperature. Herein, we study the thermal stability of 1D PCs by post-thermal self-assembly. In general, the 1D PCs with lamellar structures are prepared by solvent annealing self-assembly of bottlebrush block copolymers with hard main chain, polystyrene-block-poly(tert-butyl acrylate) (H(PS-b-PtBA)). At temperatures higher than the glass transition temperature of side chains and main chain, the 1D PCs start to post self-assembly, which reaches equilibrium state when treated at high temperature for 8 h. Correspondingly, the reflectance of the 1D PCs red shifts from purple to blue gradually with temperature increase. Scanning electron microscope characterization shows that after thermal treatment, the domain spacing of the lamellar phases is increased from 108 nm to 160 nm, which results in the red shift of the reflectance wavelength. The red shift of the 1D PCs is related to the metastable self-assembly of bottlebrush block copolymers, which will further self-assemble at high temperatures to increase the domain spacing. After reaching equilibrium, the 1D PCs are thermal stable, which shows potential in high temperature resistance.