Impact of Architecture of Symmetric Block Copolymers on the Stability of a Dislocation Defect

Abstract

Increasing the excess free energy (ΔFd) and lowering the free-energy barrier (ΔFb) of a defect are very critical for the preparation of defect-free ordered structures from the self-assembly of block copolymers. It is well known that chain architecture is one of the most useful variables for controlling the self-assembly of block copolymers. In this work, we have investigated ΔFd and ΔFb of a prototypical dislocation defect in the melts of various symmetric [AB]n linear and AnBn star copolymers (n = 2, 3, and 4) using self-consistent field theory together with the string method. We compare the magnitudes of ΔFd and ΔFb between these different copolymers in two cases: equal χN/n and unified equivalent degree of segregation. In the case of equal χN/n, [AB]n linear copolymers have a much lower ΔFd and ΔFb than AB diblock, while AnBn star copolymers have a significantly higher ΔFd but only slightly higher ΔFb. In the other case, ΔFd and ΔFb of [AB]n linear copolymers are lower and higher than those of AB diblock, respectively, but the differences decrease with increasing n. In contrast, ΔFd of AnBn star copolymers is slightly higher or comparable to that of AB diblock, and ΔFb is significantly lower than that of AB diblock. Moreover, ΔFb of AnBn continues to decrease as n increases. Our results lead to an important conclusion that AnBn star copolymers are desired by the directed self-assembly to produce defect-free stripes.