Defectivity in Laterally Confined Lamella-Forming Diblock Copolymers: Thermodynamic and Kinetic Aspects

We use self-consistent field theory (SCFT) to study the directed self-assembly of laterally confined diblock copolymers. In this study, we focus on systems in which the self-assembled lamellae are oriented parallel to selective sidewalls in a channel. While well-ordered, perfect lamellae are observed in narrow channels both experimentally and numerically, undesirable defective structures also emerge. We therefore investigate the energetics of two categories of isolated defects (dislocations and disclinations) for various segregation strengths and channel dimensions, and establish conditions that favor the formation of defects. We also determine the energy barrier and the transition path between defective and perfect states using the string method. We find that only a few kT of energy are necessary to overcome the kinetic barrier and remove a defect, sharply contrasting with the large gain in free energy (many tens of kT) that is necessary for the formation of a defect from the pristine state.