SCFT Study on Topological Defects of Symmetric Block Copolymers

Block copolymers, as typical soft material, have a long relaxation time and are highly susceptible to thermal fluctuations, and thus their self-assembly is often accompanied by the occurrence of a variety of defects. At present, most research focuses on some simple defects in AB diblock copolymer melts, and there are few studies on the influence of block copolymer architectures on defect stability. Herein, the stability of various defects in (AB)_n linear and A_nB_n star block copolymer systems is investigated by self-consistent field theory (SCFT) and string method. We calculate the excess free energy of different defects and barriers of defect-removal in different symmetric block copolymers with the same effective segregation. The comparison of excess free energy between different defects indicate that the creation of a defect with more disconnections cost higher free energy. Moreover, our results demonstrate that (i) whether for linear or star block copolymer systems, the relationship between n and the excess free energy of a defect of the block copolymer is not monotonic and (ii) the same defect has different minimum free-energy path in different block copolymer systems.