Coarse-grained molecular dynamics model of AB diblock copolymers composed of blocks with different Lennard-Jones parameters forming lamellar structures

K Hagita and T Murashima, POLYMER, 304, 127132 (2024).

DOI: 10.1016/j.polymer.2024.127132

In thermoplastic elastomers, the structure formation of hard and soft domains and the mechanical response to deformation remain vital areas of interest. To realize the coarse-grained molecular dynamics (CGMD) simulations of systems incorporating the difference in glass transition temperature T-g between domains, we studied AB diblock copolymers (di- BCPs) with asymmetric Lennard-Jones (LJ) parameters (the strength coefficient epsilon(LJ) and cutoff length r(c)). For instance, hard and soft domains were realized by assigning the cutoff lengths of each segment to r(c,(A,A)) = 2.5 (high T-g) and r(c,(B,B)) = 1.5 (low T-g), respectively. To identify how the cutoff length r(c,(B,B)) corresponds to the strength coefficient epsilon((B,B)) in the phase separation behavior against the fixed LJ parameters for the A block (r(c,(A,A)) = 2.5 and epsilon((A,A)) = 1.0), we focused on lamellar structures in which the A and B blocks possess equal segment numbers. For the asymmetric cases with r(c,(B,B)) < r(c,(A,A)), we estimated the effective epsilon((B,B))' on the basis of the D-A/D-B ratio of the partial domain spacings. We confirmed that the scaling relations (D similar to Delta epsilon (1/6), D/N-0.7 similar to Delta epsilon, and D/N-1/2 similar to Delta epsilon N) hold, where epsilon((A,A)) = 1, Delta epsilon = ((1 + epsilon((B,B))')/2 - epsilon((A,B))), and N denotes the number of segments per AB di-BCP chain. Therefore, this work will provide valuable insights for guiding applied research on BCPs.

Return to Publications page