Simulation of nucleation dynamics at the cylinder-to-lamellar transition in a diblock copolymer melt

Abstract

We examine the dynamical evolution of a stable lamellar phase nucleating from a metastable cylinder phase in a diblock copolymer melt, through large-scale simulations of the time-dependent Landau–Brazovskii model. Ellipsoidal nuclei form, whose minor axis is parallel to the cylinder axis. We use our observation of both shrinking and growing droplets to determine the critical nucleus size as a function of undercooling, and find that the critical size grows as we approach coexistence. The nucleus shape and critical size agree, near coexistence, with the predictions of an approximate theory. This supports the idea that the underlying microstructure produces an anisotropic droplet interfacial tension, and that the interplay between this interfacial tension and a reduction in bulk free-energy is central to the nucleation process. The nucleus interface moves with a time-independent velocity that depends on the interface orientation in a manner that preserves the ellipsoidal droplet shape into the late stages of growth. Near coexistence, the magnitude of the interfacial velocity varies linearly with undercooling, consistent with theoretical predictions and experimental observations.