Dynamic Masks and External Fields in Periodic Self-Consistent Field Theory: A Case Study on Double-Gyroid Thin Films

Self-consistent field theory (SCFT) accurately models the equilibrium thermodynamics of polymeric systems, including those under geometric confinement. Confinement is typically imposed in SCFT using a mask that modifies the incompressibility constraint─an approach that is limited to systems with rigid boundaries. Here we derive a “dynamic mask method” that allows a nonrigid boundary to be modeled within standard periodic SCFT by optimizing the confining geometry during a single calculation. The method requires only that the confining geometry be defined in terms of the lattice parameters of the calculation box. A corresponding technique is also derived to optimize externally imposed chemical potential fields. The method is then used to model thin films of self-assembled diblock polymers in a high-throughput manner, where the film thickness can be relaxed within a single SCFT calculation to a commensurate value that minimizes the areal excess free energy. Specifically, we extend our previous work on thin films of the double-gyroid phase, revealing that changes in segregation strength χN and conformational asymmetry b_A/b_B do not significantly affect the relative stability of different orientations of the double gyroid, meaning that the “boundary frustration” model developed previously is generalizable to any neat melt of AB diblock polymer.