Flow-induced orientation transition in charged diblock-copolymer melts

PM Moirangthem and LS Shagolsem, MOLECULAR PHYSICS, 123 (2025).

DOI: 10.1080/00268976.2025.2464064

We present a comprehensive study on the rheological behaviour of a charged diblock-copolymer (DBC) melt under confinement by using molecular dynamics simulation. Lamellae-forming, symmetric DBCs with charged A-block and neutral B-block are considered. In this study, we have focused on systems with moderate charge fraction (i.e. 11% in the A block) with equal number of explicit counterion particles added for charge neutrality. At the considered value of moderate charge fraction, the system maintains vertically oriented lamellae to which a mechanical shear is applied in transverse mode to investigate the response of the system. It is observed that when the shear rate is above a critical value, the vertically oriented lamellae inclined along the shear direction undergo an orientation transition in both charged and reference neutral systems. The critical shear rate for the charged system is lower than that of the neutral system. We systematically investigate how the individual chain conformation, alignment and counterion charge distribution depend on the shear rate. Finally, the onset of shear-thinning occurs at a lower shear rate for charged system, with a similar behaviour observed for the kinetic friction coefficient due to the differences in the spatial distribution of counterions/nanoparticles.

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