Impact Of Architecture Of Symmetric Block Copolymers On The Stability Of A Dislocation Defect

Increasing the excess free energy (Delta F-d) and lowering the free-energy barrier (Delta F-b) 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 Delta F-d and Delta F-b of a prototypical dislocation defect in the melts of various symmetric [AB](n) linear and A(n)B(n) star copolymers (n = 2, 3, and 4) using self-consistent field theory together with the string method. We compare the magnitudes of Delta F-d and Delta F-b between these different copolymers in two cases: equal chi N/n and unified equivalent degree of segregation. In the case of equal chi N/n, [AB](n) linear copolymers have a much lower Delta F-d and Delta F-b than AB diblock, while A(n)B(n) star copolymers have a significantly higher Delta F-d but only slightly higher Delta F-b. In the other case, Delta F-d and Delta F-b of [AB](n) linear copolymers are lower and higher than those of AB diblock, respectively, but the differences decrease with increasing n. In contrast, Delta F-d of A(n)B(n) star copolymers is slightly higher or comparable to that of AB diblock, and Delta F-b is significantly lower than that of AB diblock. Moreover, Delta F-b of A(n)B(n) continues to decrease as n increases. Our results lead to an important conclusion that A(n)B(n) star copolymers are desired by the directed self-assembly to produce defect-free stripes.