Field Theoretic Simulation Study of Order-to-disorder Transition of Block Copolymers Confined within Neutral Surfaces

Abstract

In this study, we investigated the order-to-disorder transition (ODT) behavior of multiple-layered cylinder- and lamella-forming block copolymer (BCP) films with neutral boundary conditions. The self-consistent field theory (SCFT) and Langevin field theoretic simulation (L-FTS), which is one of the partial saddle point approximation methods, are used to figure out the influence of wetting condition on the phase transition behavior. The SCFT study showed that (χN)ODT value of lamella-forming BCPs with neutral wetting condition increases as film thickness decreases, and it is consistent with experimental results. However, phase behavior of cylinder-forming BCPs confined within neutral surfaces was unsettled with SCFT which ignores composition fluctuation effect. In order to account for the fluctuation effect, we implemented L-FTS of discrete chain model under confinement. Ultraviolet divergence is eliminated by renormalization and calibration of Flory-Huggins parameters, allowing accurate comparison of (χN)ODT changes. By performing L-FTS with experimentally relevant invariant polymerization index, we showed that (χN)ODT value of cylinder-forming BCPs within neutral interfaces increases as the film thickness decreases, which is a consistent result with experiments.