Yielding Behavior of Bottlebrush and Linear Block Copolymers

Block copolymers can exhibit a pronounced yield stress, but the impact of molecular architecture, chemistry, and self-Assembly on macroscopic rheology remains poorly understood. Here, we study the linear-viscoelastic and yield-stress fluid behavior of two architectures-bottlebrush copolymers (with statistical or blocky sequences) and linear diblocks-that self-Assemble into body-centered cubic (BCC) spheres and hexagonally close-packed cylinders (HEX). The dynamic properties of these polymers were probed by oscillatory frequency and amplitude sweeps at temperatures well below the order-disorder transition (TODT) to furnish insights into the yielding transition. All BCC-forming polymers have a similar signature of yielding: smaller yield strains (γy,BCC ≈ 0.053 < γy,HEX ≈ 0.18), sharper solid-liquid transitions, and better reversibility than HEX. Statistical bottlebrushes show the most frequency-independent structural modulus (G0) and no signs of defect relaxation. A simple power-law relationship captures the dependence of the normalized structural modulus (G0/RT) on the inter-micelle distance (d) across different architectures and morphologies [G0/(RT) = 1.31 × 104 (nm2.6 mol/m3) d-2.6]. These studies establish quantitative structure-property relationships that are relevant in contemporary applications, for example, extrusion-based 3D printing.