In-Situ Small-Angle Neutron Scattering from a Block Copolymer Solution under Shear

Abstract

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.

Viscoelastic Properties of Low Molecular Weight Symmetric Poly(styrene-<i>b</i>-2-vinylpyridine)s in the Ordered and Disordered States under Steady Shear Flow

“…However, the J e values obtained for 3 samples in the disordered state are all higher than those of PS, implying that fluctuation effects are more pronounced for elastic behaviors than for η, qualitatively consistent with previous studies. [15][16][17][18][19] In Therefore, we can conclude that no discontinuity of η 0 and J e occur by ODT for SP melts, consistent with the results for SP solutions.…”

“…15,16) In a few studies, flow induced ordering are reported in the quiescent disordered states close to the ODT. [17][18][19] In the quiescent ordered states, G'(ω ) and G"(ω ) show power law dependence on ω (G', G" ~ ω 1 / 2 ) at the low ω end. 14,15,20) This behavior can be theoretically explained by the large scale motions of randomly oriented grains/defects 21) and/or by chain relaxation mechanism of entangled component polymers (chain retraction modes).…”

Morphology of Highly Textured E/EP Diblock Copolymers

“…It is necessary to know whether or not the melt is homogeneous or heterogeneous, i.e., the position of the order-disorder temperature, TORT, relative to the selected processing temperature, so that the corresponding thermorheologically simple [1] or complex (2,3] behavior can be anticipated. Also of importance is the sensitivity of the order-disorder temperature to changes in process variables such as applied stress or shear rate [4,5]. Finally, it is becoming increasingly apparent that processing a single block copolymer material near ToDr can lead to a variety of morphologies in the final product depending upon the process conditions employed [6, 7,8,9].…”

Orientations of the lamellar phase of block copolymer melts under oscillatory shear flow

“…Balzara et. al noticed 18 that in equilibrium the walls of shear cell induce the parallel alignment through the whole 0.5-mm sample, while Laurer et. al observed 19 that under shear there is always a near-surface layer of the parallel lamellae independently of the bulk orientation.…”

“…To explain the second transition we make use of recent experiments 18,19 and argue that the high-frequency parallel orientation is stabilized by the preferable interaction of the shear-cell walls with on of the components of the melt. Validity of this hypothesis requires further experimental studies.…”