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 symmetric poly(ethylene propylene)–poly(ethylethylene)–poly(ethylene propylene) (PEP–PEE–PEP) triblock copolymer have been studied using small-angle neutron scattering and rheological measurements.

Shearing in the ordered state produced parallel lamellae under all steady-state conditions investigated, and the lamellar-to-disorder transition temperature decreased dramatically with increasing shear rate. Both phenomena are qualitatively different from the documented behavior of PEP–PEE diblock copolymers.

However, cooling the disordered material while shearing at a relatively low deformation rate initially induces perpendicular lamellae, analogous to the diblock response. These observations are considered in the context of theory and other experimental studies.