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

Abstract

Flow alignment in a large amplitude oscillatory shear field of lamellar AB and ABC block copolymers has been studied in bulk and in solution. Flow birefringence and 2D small-angle X-ray scattering were used to monitor the orientation. Qualitatively similar orientation behaviour was found for the diluted and the bulk AB block copolymer. While in AB diblock copolymers there is only one interface between the different blocks which may influence the orientation behaviour, in ABC triblock copolymers there are two interfaces within the macromolecule. It will be shown that the introduction of a third block leads to a quite different orientation behaviour in comparison to the AB system. In the lamellar diluted ABC system always the parallel orientation dominates, but it occurs in coexistence with the perpendicular and transverse orientations.

Nanostructured PMMA: From Lamellar Sheets to Double-Layered Vesicles

“…This transition, which is also observed when a constant shear is applied, is reminiscent of a transition exhibited by lyotropic lamellar phases in highly concentrated surfactant solutions to onion-like structures . This transition is also consistent with the formation of vesicular nanoobjects by 20 wt % of a symmetric ABC triblock prepared in a polyamide matrix by reactive blending . The nanoobjects shown in Figure are vesicles consisting of a trilayer envelope.…”

“…As a rule, the self-assembly of block copolymers is sensitive to mechanical energy input. For example, large-amplitude oscillatory shear (LAOS) was extensively used in order to extend the periodic self-assembly, mainly lamellar, to a macroscopic scale. , The longer-range alignment of lamellae was found to depend on shear frequency, amplitude, and temperature. Similar work has however not been reported for block copolymer/homopolymer blends.…”

Nonequilibrium Processes in Polymer Membrane Formation: Theory and Experiment

“…Besides single shear also large amplitude oscillatory shear is a known way to yield aligned block copolymer morphologies, where the orientation of the microdomains depends on the frequency both in bulk 348−350 and in concentrated solution. 351 Another challenging topic is block copolymer membranes with pores down to the sub-10 nm range, which requires low-molecular-weight block copolymers with a very high χ-parameter. 352 Such block copolymer membranes will likely suffer from low mechanical stability due to the lack of entanglements in the matrix blocks, a problem which may be overcome by cross-linking.…”

“…Coupling different external stress fields such as, e.g., biaxial mechanical stretching or combining uniaxial shear with an electric field during membrane casting, could influence the final membrane morphology and may become interesting for membrane formation. Besides single shear also large amplitude oscillatory shear is a known way to yield aligned block copolymer morphologies, where the orientation of the microdomains depends on the frequency both in bulk − and in concentrated solution . Another challenging topic is block copolymer membranes with pores down to the sub-10 nm range, which requires low-molecular-weight block copolymers with a very high χ-parameter .…”