Thomas R. Tepe

Shear-induced ordering kinetics of a triblock copolymer melt

Disorder-to-order transitions, in which an isotropic system acquires a spatially periodic structure, are common to a number of phenomena in materials science. Here, we employ small-angle neutron scattering to probe the effects of reciprocating shear on the isotropic-to-lamellar transition of a triblock copolymer composed of poly(ethylene-co-propylene) (PEP) and poly(ethylethylene) (PEE). Prior work has shown that the transition temperature decreases with increasing shear rate, implying that the isotropic state can be produced at low temperatures through application of a flow field [T. Tepe et al., J. Rheol. 41, 1147 (1987)]. Removing this field results in a “jump” to conditions under which the lamellar phase is stable with a time scale set by the relaxation of concentration fluctuations. We describe the ordering process which results, concentrating on the possible existence of a stability limit for the initial (isotropic) state.