Nanostructured materials through orthogonal self-assembly in a columnar liquid crystal

This paper describes a system in which an acid functionalized discotic molecule and poly(propyleneimine) dendrimer self-assemble into a new type of oblique columnar liquid crystalline (LC) phase that displays a well-ordered superlattice. The orthogonal combination of hydrogen bonding in the columnar direction and ionic interaction in the plane perpendicular to the columns gives rise to a structure in which the dendrimer is confined to separate columnar domains. The structure of the mesophases formed in the mixed system has been elucidated by infrared spectroscopy and X-ray diffraction. Investigation by differential scanning calorimetry and polarizing optical microscopy has shown that the LC phase is most stable in an 8:1 molar mixture but remains stable over a wide temperature and composition range. In dendrimer enriched mixtures the lattice swells to take up more dendrimer, while discotic enriched mixtures show the appearance of lamellar phases with a columnar structure that is probably closely related to the oblique superlattice. Additionally, the structure of the oblique superlattice can be covalently stabilized at elevated temperature via amidation of the ionic carboxylic acid-amine complexes. The results show the potential of orthogonal self-assembly in columnar LC phases to obtain nanostructured materials with a periodicity of 2-10 nm. © 2008 American Chemical Society.