Abstract
The process of flow-induced alignment in a lamellar diblock copolymer melt is investigated using simultaneous measurements of shear stress and birefringence. Flow birefringence, in situ, during oscillatory shear clarifies how the orientation distribution evolves toward either parallel or perpendicular alignment, i.e., layers normal to either the velocity gradient or the vorticity axis, respectively. A nearly symmetric, polystyrene-polyisoprene diblock (ODT ≃ 164 °C) is studied at 120 °C (T/T ODT ≃ 0.90). The critical frequency (ω' c ) associated with a crossover in the relaxation dynamics from being dominated by the macromolecular response to being dominated by the microstructural response is estimated to be ω' c 3-7 rad/s at 120 °C. At high frequencies (relative to ω' c ), shearing induces parallel alignment, while shearing at lower frequencies leads to perpendicular alignment. In all cases, alignment proceeds through a fast process followed by a slow one. The fast process is dominated by depletion of the projection of the orientation distribution along either the perpendicular direction or the transverse direction (layers normal to the flow). The resulting biaxial distribution is transformed into a well-aligned uniaxial one during the slow process. Surprisingly, the projection along the perpendicular direction can disappear faster than the projection along the transverse direction. This occurs during the fast process en route to parallel alignment with sufficiently high frequencies. As the shearing frequency is lowered, the projection along transverse orientation decreases faster than that along the perpendicular direction.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.