We develop a theory to describe the reorientation phenomena in the lamellar phase of block copolymer melts under reciprocating shear flow. We show that, similar to the steady shear, the oscillating flow anisotropically suppresses fluctuations and gives rise to the $\overrightarrow{\Vert }\perp$ transition. The experimentally observed high-frequency reverse transition is explained in terms of interaction between the melt and the shear-cell walls.

• Received 15 June 2001

DOI:https://doi.org/10.1103/PhysRevE.65.031803