Shear-induced structure and rheology of multichain amphiphilic diblock and triblock copolymers in dilute solutions

This study presents a computational investigation of self-assembly and rheological behavior of multichain amphiphilic block copolymers under varying chain length (N), architecture, composition (f), and shear rate (γ˙). Using Brownian dynamics simulations, we systematically examined bead-spring model multichain diblock and triblock copolymers with N = 12–48 beads, f ranging from 0 to 1.0, and γ˙ spanning 0–0.1 ns−1. These systems self-assemble into spherical, prolate, rodlike, and oblate/disk micelles, with transitions governed by each variable, where increasing shear rate drives nonmonotonic prolate-to-rod redistribution, aggregating at weak shear rate before fragmenting at high rates; longer chains strengthen the dominant rod population; and higher hydrophobic fraction shifts assemblies from rod toward sphere at f = 1. Triblock copolymers form bridged assemblies, where hydrophobic end-blocks anchor into distinct micellar cores while hydrophilic middle blocks span the intervening space, producing solution viscosities up to half an order of magnitude greater than counterpart diblock systems. Linear viscoelastic spectra show terminal power-law scaling (G′ ∼ ω2, G″ ∼ ω1) with a liquidlike response (G″ > G′) throughout the accessed window. The triblock relaxation is governed by chain-end escape. The bridge fraction rises with the chain length as a longer midblock spans neighboring cores but falls with hydrophobic fraction as the shorter midblock forces chains into loops. The bridge lifetime saturates with increasing chain length once bridging is established (N ≥ 24), while the loop lifetime shortens with chain length yet increases with hydrophobic fraction, providing qualitative design insights relevant to flow-responsive polymer self-assembling systems.