Collapse of theIa3¯dcubic symmetry by uniaxial stretching of a double-gyroid block copolymer

We report an experimental observation of collapse of the $\mathrm{Ia}3\mathrm{}¯d$ symmetry by stretching of an elastomeric block copolymer that forms a double-gyroid (DG) microdomain structure. Some new diffraction spots were observed for a deformed DG structure. These spots were assigned to {110} and {200} reflections. For the $\mathrm{Ia}3\mathrm{}¯d$ symmetry, these reflections are prohibited by the extinction rule and therefore none of them appeared for the sample before deformation. Appearance of these reflections indicates breakdown of the extinction rule and can be explained as a result of collapse of the symmetry of glide when three-dimensional DG networks are partially ruptured upon stretching.