The
effects of polymer chain topology on the order–disorder
transition of symmetric AB diblock copolymer melts are studied using
coarse-grained molecular dynamics simulations. Specifically, we compared
chain conformations near the lamellar-disordered transition in melts
of symmetric (i.e., 50–50) AB diblock copolymers of linear
chains, rings, and trefoil knots at the same chain lengths. The order
(lamellar)–disorder transition temperature and the domain sizes
both shifted to lower values with the introduction of topological
constraints, leading to the following sequence: linear chains >
rings
> trefoil knots. Investigation of the polymer chain conformations
in terms of their radii of gyration, their writhe values (a measure
for the degree of intertwining of a chain around itself), and their
Jones polynomials (a method to measure entanglement of curves) showed
that linear chains and rings remained stretched, while knots were
stretched and tightened in disordered melts close to the lamellar-disorder
transition. This work highlights chain topology as an important factor
in affecting microphase separation in block copolymers.
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