Bryan Kaehr1, Madeline Van Winkle2, David Scrymgeour1, Hoke Wallace2, Joseph Reczek2
- Sandia National Laboratories
- Denison University
For decades, liquid crystals (LCs) have found ubiquitous use in display technologies, operating as stimuli responsive polarizers largely based on controlled ordering of calamitic (rod-shaped) LCs. Recently, the sub-class of multi-component, columnar phase liquid crystals (CLCs) has attracted substantial investigation due to their broad potential as self-assembling and self-healing absorbers, semiconductors, and potentially room temperature ferroelectrics. These materials can exhibit synergistic charge-transfer (CT) behavior (e.g., band gap) that is tunable via simple mixing of donor/acceptor moieties, and the anisotropic nature of this CT absorption can be manipulated to form inherently dichroic films. Here, we take advantage of the functionality and chemical malleability of bi-component CLCs to develop an optically re-writable material (OWR) with fine control over dichroic properties. Films of mixed stack donor-acceptor columnar liquid crystals (DACLCs) comprised of diaminonaphthalene/ naphthalenediimide (DAN/NDI) complexes are subjected to laser-induced temperature gradients to direct columnar alignment. Fast laser scanning induces a sharp temperature gradient that leads to flash-cooling of the DACLC resulting in no long-range molecular order, with written areas becoming completely isotropic. Slower scanning leads to a sustained thermal gradient that realigns the columnar director, and the subsequent polarization axis of the region, exactly in the direction of laser movement. Using this simple mechanism, the columnar alignment and hence CT-based dichroism can be patterned intentionally and repeatedly, as we demonstrate via fabrication of reconfigurable micro-polarizers and bar codes.
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.