Dynamics of Kink Bands in Layered Liquids:  Theory and in Situ SAXS Experiments on a Block Copolymer Melt

Abstract

We consider the dynamics of an isolated kink band within an otherwise well-aligned lamellar block copolymer (or other smectic A liquid crystal) subjected to a macroscopic shear flow. We find on geometrical grounds that normal relative motion of the tilt boundaries that delineate such a band, relative to the normal velocity of the fluid, can occur only if there is jump in the tangential component of the fluid velocity across the boundary. We show that such tangential slippage should be negligible for well-developed bands with narrow boundaries. These observations lead to a simple description of the evolution of an idealized kink band, in which the kink bandwidth remains constant after the formation of narrow tilt boundaries, and the tilt boundaries rotate as material surfaces in a shear flow. The resulting prediction for the rate of rotation of the layers within such a band is confirmed by in situ small-angle X-ray scattering (SAXS)-steady shear experiments, which measure the evolution of the distribution of lamellar orientations within kink bands in a predominantly parallel poly(styrene-co-ethylenepropylene) diblock copolymer.

Three‐Dimensional Observations of Grain Boundary Morphologies in a Cylinder‐Forming Block Copolymer

“…In the TGB, on the other hand, the plane is parallel to the boundary surface. The KGB of block copolymers has been intensively studied, both experimentally [6,[8][9][10] and theoretically. [11] Thomas et al proposed the doubly periodic morphology approximating Scherk's first surface as a model for the TGB simply due to the minimization of the surface area, [12] which was later confirmed experimentally by Jinnai et al [13] In contrast to the KGB, there are only a few experimental studies concerning the structure of TGBs in the literature [6,7] and, to our best knowledge, there are no study dealing with the grain boundaries in the cylinder-forming block copolymers.…”

Orientation behaviour of AB and ABC block copolymers under large amplitude oscillatory shear flow in bulk and in concentrated solution

“…Besides orientation of block copolymers also morphological defects induced by shear have attracted interest [21,24,[59][60][61]. In the following, focus will be on works dealing with lamellar block copolymers.…”

Deformation and alignment of lamellae in melt extension of blends of a styrene‐butadiene block copolymer with polystyrene

“…The influence of the molecular architecture of several styrene-butadiene triblock copolymers with similar styrene and butadiene content was investigated by Thunga et al 26 The dynamics of kink bands in a shear field was determined using electron microscopy and small angle X-ray scattering in Refs. 17,18. The work of Geiger et al was devoted to the rheology of triblock copolymers under extrusion conditions.…”