Continuum models for directed self-assembly

Abstract

The computational description of directed self-assembly (DSA) of copolymer materials requires the prediction of large-scale structure formation of copolymer materials guided by chemical or topographical patterns. The disparity between the periodicity of self-assembled structures and the large length scale of devices poses computational challenges that requires the use of highly coarse-grained models. The highest level of coarse-graining is achieved by continuum models that integrate out the molecular degrees of freedom and describe the system only by the local composition. We evaluate the abilities of two continuum models – the Swift–Hohenberg and Ohta–Kawasaki free-energy functionals – to describe directed self-assembly qualitatively and quantitatively by comparison to self-consistent field theory and particle-based simulations, illustrating applications to defect motion and annihilation and the design of guiding patterns for fabricating device-oriented structures. We devise a phenomenological mapping between the Ohta–Kawasaki model and the standard Gaussian chain model of block copolymers, highlight the advantages of the Ohta–Kawasaki model and discuss the significance of the disparity between the characteristic length scale of surface-directed spinodal self-assembly and the equilibrium domain spacing.