Small-angle neutron scattering profiles from linear polystyrene-polyisoprene block copolymers were measured as a function of temperature. Measurements were made on eight diblock copolymers and two triblock copolymers, with molecular weights ranging from 1.2 104 to 4.1 104 and ranging from 0.13 to 0.46 ( is the volume fraction of the minor component). The scattering profiles were consistent with the mean-field theory of Leibler for block copolymers with 0.25 < < 0.5. Fluctuation corrections proposed by Fredrickson and Helfand were found to be increasingly important as the order-disorder transition was approached. However, large deviations between experiment and theory were observed in low molecular weight asymmetric block copolymers with < 0.25. The amplitude of the concentration fluctuations was found to be an order of magnitude larger than predictions by Leibler, and Fredrickson and Helfand. These findings cannot be explained on the basis of a composition-dependent Flory-Huggins parameter because this anomaly is not evident in a higher molecular weight block copolymer with the same asymmetry ( ).

Small-angle neutron scattering profiles from a concentrated (65 wt % ) polystyrene-polyieoprene block copolymer solution in dioctyl phthalate under shear were obtained both above and below the quiescent order-disorder transition (ODT). The ordered solution has a lamellar structure under quiescent conditions. The shear-induced structure was inferred from scattering measurements in two planes: the v-vxVv plane and the Vv-VXVU plane (v is the fluid velocity direction and Vv is the velocity gradient direction). Below the quiescent ODT, oscillatory shear produces lamellae that are aligned along the shearing surface, while steady shear results in a reorientation of the lamellae normals from the v-vxVv plane to the Vu-vxVv plane. Above the quiescent ODT, steady shear induces order above a critical shear rate. The resulting scattering anisotropy obtained at different temperatures obeys a universal scaling law, and the critical shear rate increases exponentially with temperature.

The effect of shear flow on a concentrated block copolymer solution with lamellar microstructure was studied by in-situ small angle neutron scattering. Microstructural changes were determined from scattering measurements in all three principal directions (flow, velocity gradient, and neutral directions). The lamellae were found to align along the velocity direction but exhibited two orientations:  one parallel to the shearing surfaces and the other perpendicular to the shearing surfaces. The perfection of the perpendicular alignment was always significantly greater than that of the parallel alignment. In fact, our sample in the parallel alignment was, to a large extent, disordered (i.e., liquid-like). In some cases, we found transient, well-aligned, perpendicular lamellae that eventually degenerated to poorly ordered, parallel lamellae. In one case, a systematic increase in lamellar undulations was evident prior to disordering. These results are not in agreement with current theories, which only predict enhanced order in block copolymers under shear flow.

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