Self-Assembly of Macromolecules within Single Topological Defects of Nematic Solvents

Solvent-mediated self-assembly of macromolecules has been widely used as a bottom-up strategy for the synthesis of nanostructured materials, but most solvents (e.g., water or isotropic organic solvents) provide limited control over the spatial localization and manipulation of individual assemblies. In this study, we use organic solvents with nematic ordering to explore the possibility of programmed assembly of polymers with tailored side chains within the nanoscopic cores of topological defects of the nematic solvents by developing structure-property relationships. Variation of the side chains of poly(n-alkyl acrylates) (alkyl = butyl, hexyl, and dodecyl) revealed that the driving force for the partitioning of the polymers into the nanoscopic cores of topological defects formed in nematic 4′-n-pentyl-4-biphenylcarbonitrile (5CB) increased with side-chain length, but controlled self-assembly was not observed. Poly(dimethylacrylamide) was found to be soluble in bulk nematic 5CB but did not partition to defects and poly(2-hydroxyethyl acrylate) aggregated in the nematic solvents prior to partitioning to defects. However, poly(2-hydroxyethyl methacrylate) preferentially partitioned into defects above a critical concentration, forming single, well-defined, and reversible assemblies (in the absence of aggregation in the bulk phase) at locations defined by the positions of the defects. By synthesizing copolymers that incorporated anthracene side chains, photo-cross-linked assemblies with cross-section diameters of 30 ± 5 nm could be generated in and recovered from the defects. Overall, this study provides design parameters for programmed polymer assembly in topological defects of liquid crystalline solvents, including the polymer side-chain structure (polarity, flexibility, and hydrogen bonding properties), polymer molecular weight, and properties of the main chain.