Absorption-Desorption Isotherms for Understanding the Self-Assembly of Block Copolymer Supramolecules

Self-assembled block copolymers (BCPs) are known to be a great candidate for nanolithography. While being excellent in their parent nature, the chemical diversity and functionality of BCPs can be further enhanced by small molecule complexation. Complexed block copolymers allow us to create an added dimension to tune the volume fractions, feature sizes of the resulting morphologies, and interactions between the blocks, and access to rapid self-assembly without the complexity of time and energy consuming synthetic routes. For instance, addition of 3-pentadecylphenol to a polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) BCP further alters the Flory-Huggins interaction parameter (χ) between the PS and P4VP blocks influencing strong phase segregation that could benefit lithography applications by creating sharpened patterns. The high χ of these BCP complexes eliminates thermal annealing for self-assembly driven ordering and calls for solvent vapor annealing (SVA) instead. The dynamic nature of SVA further complicates the self-assembly mechanisms. Although controlled SVA can be engineered, understanding of the resulting kinetics of these multicomponent systems is scarce. We previously introduced absorption-desorption isotherms as a method to deconvolute the self-assembly kinetics of PS-b-P4VP(PDP). However, a deeper understanding of the potential of isotherms is necessary. In this work, we use absorption-desorption isotherms to investigate the diffusion of the small molecule into the non-complexing block. Further, we use the isotherms to understand the effect of solvent selectivity in self-assembled morphologies. This method can be extended to supramolecules that form other lattice structures. Through this work, we intend to universally establish isotherms as a unique characterization technique to simplify the underlying kinetics of supramolecular self-assembly under controlled SVA.