Abstract
We study concentration dependence of the critical shear rate of a layer orientation transition in lyotropic triblock copolymer lamellar phase. Theory predicts that suppression of undulation fluctuation by shear triggers the transition. The critical shear rate at high polymer concentration is in reasonable agreement with theory. However, experimental results at low polymer concentrations show different behavior from the prediction. Violation of the theory is attributed to defective nature of the lamellar phase, in which creation of defects prevents the suppression of the undulation fluctuation.
