Scalable Processing of Large Area, Oriented 2-Dimensional Polymer Films

2-dimensional polymers (2DPs) such as covalent organic frameworks (COFs) are an emerging class of materials which have displayed significant potential in applications ranging from catalysis, energy storage, dielectrics, nanofiltration, gas storage, and mechanically robust engineering materials. They are synthesized from geometrically pre-defined building blocks and can accommodate a wide variety of pore shapes, sizes, and functionality. Most methods used to produce 2DPs result in an insoluble microporous powder that cannot be processed into a functional form factor which limits their relevance in commercial or military applications. Despite these challenges, a variety of creative approaches have been explored to process 2DPs into films, composites, or gels. Top-down methods such as exfoliation or solution casting or bottom-up methods that form films directly from cast monomer solutions have been used to varying levels of success to access films and membranes. Interfacial polymerization has also been used to form films at the interface of two immiscible solvents. Despite this progress, many of the available techniques suffer from limitations that preclude further elaboration into industrially relevant processing techniques or lead to formation of films of poor quality. Exfoliation based approaches are low-yielding and solution casting techniques often involve appending solubilizing groups to the pore wall which can block access to the pore itself. Methods that cast directly from monomer solution can be scaled up in a roll-to-roll process but often result in films that are mechanically weak as it is difficult to control the size and orientation of the individual 2DP sheets and they often lack sufficient intermolecular interactions. More work is needed to understand the underlying kinetics and thermodynamics of the film forming processes as it relates to monomer selection, layer alignment, domain size, and formation of defects. New engineering approaches are also needed to further control film formation, thickness, functionality, and orientation during deposition and post-processing. Special focus should be given to controlling and minimizing defects that could mitigate material performance: point and stacking defects within 2D polymer crystals, stacking defects in between crystallites, pinholes, and residual solvent / reactant contaminations within the films, crystallite size distributions to name a few. The objective of this topic is to develop a scalable, cost-effective method to produce large area 2DP ensemble films with superb control over structural evolution. Designed processes must consider monomer composition, long range structural order in lateral and parallel planes, interlayer interactions and flaw tolerance. The process should be amenable to roll-to-roll processing or a related method to produce continuous films.