INFLUENCE OF SHEAR ON A LAMELLAR TRIBLOCK COPOLYMER NEAR THE ORDER-DISORDER TRANSITION

The effects of a large strain (600%) reciprocating steady shear on the lamellar orientation and the order-disorder transition of a nearly sy mmetric poly(ethylene propylene)-poly(ethylethylene)-poly(ethylene pro pylene) (PEP-PEE-PEP) triblock copolymer have been studied using small -angle neutron scattering and rheological measurements. Shearing in th e ordered state produced parallel lamellae under all steady-state cond itions investigated, and the lamellar-to-disorder transition temperatu re decreased dramatically with increasing shear rate. Both phenomena a re qualitatively different from the documented behavior of PEP-PEE dib lock copolymers. However, cooling the disordered material while sheari ng at a relatively low deformation rate initially induces perpendicula r lamellae, analogous to the diblock response. These observations are considered in the context of theory and other experimental studies. (C ) 1997 The Society of Rheology.