Nanoscale View of\nAlignment and Domain Growth in a\nHexagonal Columnar Liquid Crystal

Highly ordered liquid crystalline (LC) phases have important\npotential\nfor organic electronics. We studied the molecular alignment and domain\nstructure in a columnar LC thin film with nanometer resolution during\nin situ heating using four-dimensional scanning transmission electron\nmicroscopy (4D STEM). The initial disordered vapor-deposited LC glass\nthin film rapidly ordered at its glass transition temperature into\na hexagonal columnar phase with small (<10 nm), well-aligned, planar\ndomains (columns oriented parallel to the surface). Upon further heating,\nthe domains coarsen via bulk diffusion, then the film crystallizes,\nthen finally transforms back to an LC phase at an even higher temperature.\nThe LC phase at high temperature shows straight columns of molecules,\nwhich we attribute to structure inherited from the intermediate crystalline\nphase. Nanoscale 4D STEM offers direct insight into the mechanisms\nof domain reorganization, and intermediate crystallization is a potential\napproach to manipulate orientational order and texture at the nano-\nto mesoscale in LC thin films.