Multiscale Modeling of Grain-Boundary Motion in Cylinder-Forming Block Copolymers

Using the combination of a soft, coarse-grained, particle-based model, a free-energy functional that depends on the local composition, and a lattice model of local, metastable states, we study the structure and motion of a grain boundary between two orthogonal grains of cylindrical domains in asymmetric block copolymers. The particle-based model provides direct insights into the elementary class of transitions of the self-assembled morphology in the course of grain-boundary translation. These processes are correlated in space and time. We identify a minimal set of transitions, whose free-energy changes and barriers are obtained by describing the system by a free-energy functional of the local composition and calculating the minimum free-energy path (MFEP). The spatiotemporal correlation arises from the dependence of the free-energy characteristics on the local environment. We use this information to parametrize a lattice model of the correlated processes in the course of grain-boundary motion. This allows us to investigate the grain-boundary motion by kinetic Monte Carlo (kMC) simulation and determine its free-energy landscape. Grain-boundary motion proceeds by nucleating a two-dimensional, anisotropic cluster inside the plane of the grain boundary.