Small Volume-Fraction Limit of the Diblock Copolymer Problem: II. Diffuse-Interface Functional

We present the second of two articles on the small volume-fraction limit of a nonlocal Cahn–Hilliard functional introduced to model microphase separation of diblock copolymers. After having established the results for the sharp-interface version of the functional [SIAM J. Math. Anal., 42 (2010), pp. 1334–1370], we consider here the full diffuse-interface functional and address the limit in which ε and the volume fraction tend to zero but the number of regions (called particles) associated with the minority phase remains O(1). Using the language of Γ-convergence, we focus on two levels of this convergence, and derive firstand second-order effective energies, whose energy landscapes are simpler and more transparent. These limiting energies are finite only on weighted sums of delta functions, corresponding to the concentration of mass into “point particles.” At the highest level, the effective energy is entirely local and contains information about the size of each particle but no information about its spatial distribution. At the next level we encounter a Coulomb-like interaction between the particles, which is responsible for the pattern formation. We present the results in three dimensions and comment on their two-dimensional analogues.