Ordering Kinetics and Alignment of Block Copolymer Lamellae under Shear Flow

Abstract

The effect of large-amplitude oscillatory shear flow on a concentrated block copolymer solution with lamellar order was studied by in-situ small-angle neutron scattering. Microstructural changes were studied as a function of temperature, frequency of the oscillatory flow field, and thermal history prior to turning on the shear field. We find that the alignment path depends mainly on thermal history prior to turning on the shear field and is independent of frequency and temperature. At long times, the lamellae were aligned parallel to the shearing plates, regardless of frequency, temperature, and thermal history. We refer to this as the parallel orientation. Monotonic changes from the unaligned to the aligned state were found when the shear field was turned on after the sample was completely ordered. The alignment kinetics, in this case, occurs in two stages. The first stage consists of a rapid rotation of the grains so that the lamellar normals lie in the velocity gradient-vorticity plane. This is followed by a slower process wherein the lamellar normals get increasingly localized in the velocity gradient direction. We also studied ordering kinetics under shear, by turning on the shear field before significant ordering had taken place. In this case, the first stage of ordering resulted in the formation of lamellae aligned perpendicular to the shearing plates in addition to the parallel lamellae, regardless of temperature and frequency. Eventually the perpendicular lamellae were transformed to parallel lamellae via an undulation instability.

Association properties of diblock copolymer of ethylene oxide and 1,2-butylene oxide: E17B12 in aqueous solution

“…The rheology summarized in Figs. 8, 9, 13 and 14 provides strong evidence favoring worm-like micelles since the lamellar phase of a block copolymer solution should not exhibit the behavior of a Maxwell fluid in the linear viscoelastic regime [38,39]. We also emphasize the SANS evidence for formation of worm-like micelles on heating dilute aqueous solutions of the related copolymer E 18 B 10 [3].…”

Shear-induced instabilities in layered liquids

“…Furthermore there is a reversible coupling between the layer displacement and the velocity field in equation (16). But its coupling constant has to be unity due to the Gallilei invariance of the equations.…”

Progress in control of microdomain orientation in block copolymers – Efficiencies of various external fields

“…The former category involves the LAOS technique where the lamellar orientation depends not only on frequency but also the strain amplitude. While frequency dependence has well been known [36][37][38], strain amplitude dependence has been also noticed [34]. The former researches have documented the perpendicular orientation at small frequency and parallel orientation at high frequency.…”