Self-consistent Field Theory and Langevin Field Theoretic Simulation of Order-to-Disorder Transition of Block Copolymers in Thin Film

Abstract

It is well known that the ordering of AB diblock copolymer (BCP) thin films is affected by the surface interaction. However, there have been ongoing debates on the direction of change in the order-to-disorder transition (ODT) temperature or (χN)ODT with respect to the type of the surface interaction. We investigated the (χN)ODT movement of cylinder- and lamella-forming BCP films in a series of recent research through collaboration with experimentalists. The self-consistent field theory (SCFT) using discrete chain model reveals that when the thin film is confined within two preferential walls, (χN)ODT value decreases as the film thickness decreases, and this result is confirmed by the experiment. On the other hand, if the two walls are neutral to the two blocks, the direction of the (χN)ODT movement turns out to be the opposite. This trend persists when one wall is neutral and the other wall is not so strongly preferential, and this result is also consistent with the experiment. For the study of the phase behavior of cylinder-forming BCPs confined within neutral surfaces, we further performed Langevin field-theoretic simulation (L-FTS) which accounts for the compositional fluctuation effect. After the removal of ultraviolet divergence through renormalization of Flory-Huggins parameters, the (χN)ODT value of cylinder-forming BCPs within neutral interfaces turns out to increase as the film thickness decreases when the invariant polymerization index is within the experimental range.