Shear Instability of the Gyroid Phase of a Diblock Copolymer

For lamellar (symmetric) diblock copolymers it is well established that mechanical shear couples to composition fluctuations in the melt state. Both theory and experiment show that the order-disorder transition temperature TODT increases with the oscillatory shear amplitude. The result is a more mean field-like state under shear. The influence of these composition fluctuations is to stabilize the gyroid phase, which is the equilibrium morphology close to the TODT of asymmetric diblock copolymers. Therefore, it is tempting to ask: “Is the cubic bi-continuous gyriod phase stable when exposed to large amplitude oscillatory shear?”