Ordering and Grain Growth in Charged Block Copolymer Bulk Films: A Comparison of Solvent‐Related Processes

Abstract While prior efforts have demonstrated that the morphologies of block copolymer (BC) bulk films can be controlled through judicious chemical design and thermal annealing, recent interest has focused on regulating the orientation of BC nanostructures and minimizing defects. Thermal processes developed to achieve this purpose for nonpolar BCs are not, however, suitable for orienting microphase‐ordered BCs composed of at least one block with charged moieties that can form thermally stable ionic clusters. To overcome this challenge, we have previously applied solvent‐vapor (SV) annealing to block ionomer (BI) bulk films composed of midblock‐sulfonated pentablock copolymers and established that this approach yields highly ordered morphologies that display evidence of improved in‐plane orientation. Here, we employ small‐angle X‐ray scattering to compare the effectiveness of three solvent‐related processes–SV annealing, SV permeation, and SV sorption–on BI ordering and grain growth, and offer explanations for observed differences on the basis of thermodynamic‐ and transport‐related considerations. Differences in the experimental design of these solvent‐related processes are found to affect nanostructural development, as evidenced by the extent of in‐plane grain growth.