Blue phase liquid crystals in a Grandjean–Cano cell

Blue phase liquid crystals are soft photonic crystals that are of interest for sensing and display applications. In recent years, considerable progress has been made in forming blue phase single crystals on chemical patterns. Blue phase single crystals are appealing for technological applications owing to their optical homogeneity. To study single crystal formation when the thickness is incommensurate with blue phase lattice size we prepare cells with a thickness gradient or a “Grandjean–Cano cell”. We observe formation of stripes in the direction perpendicular to the thickness gradient in blue phase single crystals. The stripes occur at a thickness interval significantly smaller than the lattice size. To understand the origin of these mysterious stripes we perform Landau-de Gennes based continuum simulations. Based on experimental and theoretical findings we speculate that the spacing between stripes is related to the size of double twist cylinders in the blue phase.