THE EFFECT OF ADDED TRIBLOCK COPOLYMER ON THE NONLINEAR RHEOLOGY OF ORDERED DIBLOCK COPOLYMER MESOPHASES

We present a phenomenological theory for the rheological behavior of o rdered mesophases of mixed diblock and triblock copolymer under shear. This theory is based on a coupled multilayer model for mesophase dyna mics, and represents the extension of an earlier theory [Doi et al., M acromolecules 26, 4935 (1993)] for pure diblock copolymer mesophases. We show that added triblock copolymer suppresses yielding behavior in copolymer mesophases. We discuss the possible relevance of our model t o experimental rheological and structural studies of microphase-separa ted diblock+triblock copolymer solutions in selective solvents. (C) 19 96 Society of Rheology.