Phase diagrams of conformationally asymmetric pentablock copolymer melts: a theory and simulation study.
basic_science · Level V
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- Record sourced from PubMed, PMID 41879830.
- Also identified by DOI 10.1039/d5sm01223f.
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Abstract
Conformational asymmetry, a difference in Kuhn length between two monomers, is known to shift the order-order transition (OOT) boundaries of block copolymer (BCP) melts and stabilize complex morphologies (<i>e.g.</i>, Frank-Kasper phases) with enticing optical and transport properties. In this work, we investigate the influence of conformational asymmetry on the self-assembly of A<sub><i>x</i></sub>B<sub><i>y</i></sub>A<sub><i>z</i></sub>B<sub><i>y</i></sub>A<sub><i>x</i></sub> pentablock copolymers (pentaBCPs) by adopting our previously developed workflow involving self-consistent field theory (SCFT) calculations and coarse-grained (CG) molecular dynamics (MD) simulations aided by the RAPSIDY protocol. For varying conformational asymmetry ratios, CAR ≡ <i>β</i><sub>A</sub>/<i>β</i><sub>B</sub>, where <i>β</i><sub><i>i</i></sub> is related to the Kuhn length of each block, SCFT shows shifts in the OOTs as CAR changes. For example, as CAR increases, the stability window widths of the hexagonally closed-packed cylinder and body-centered cubic spherical phases expand. To further understand the effect of CAR on chain conformations, we conduct MD simulations using two CG models - the 'semiflexible' chain model and the 'unequal-bead-diameter' (UBD) model. To vary CAR, in the 'semiflexible' chain model we vary the stiffness of A and B blocks, and in the UBD chain model we vary the A bead diameter with respect to the B bead diameter. The simulated phase behavior is qualitatively similar with both models and agrees to a large extent with the predicted phase diagram from SCFT. The normalized chain end-to-end distance and A-B interface width are consistent between both models and generally insensitive to CAR. However, the normalized lamellae periodicity expands with increasing conformational asymmetry (<i>i.e.</i>, as CAR moves away from 1) for the semiflexible chain model, and the opposite is observed with the UBD chain model.