Quantized Self-Assembly of Discotic Rings in a Liquid Crystal Confined in Nanopores
journal contributionposted on 25.09.2020, 13:56 authored by Kathrin Sentker, Arne W Zantop, Milena Lippmann, Tommy Hofmann, Oliver H Seeck, Andriy V Kityk, Arda Yildirim, Andreas Schönhals, Marco MazzaMarco Mazza, Patrick Huber
Disklike molecules with aromatic cores spontaneously stack up in linear columns with high, one-dimensional charge carrier mobilities along the columnar axes, making them prominent model systems for functional, self-organized matter. We show by high-resolution optical birefringence and synchrotron-based x-ray diffraction that confining a thermotropic discotic liquid crystal in cylindrical nanopores induces a quantized formation of annular layers consisting of concentric circular bent columns, unknown in the bulk state. Starting from the walls this ring self-assembly propagates layer by layer towards the pore center in the supercooled domain of the bulk isotropic-columnar transition and thus allows one to switch on and off reversibly single, nanosized rings through small temperature variations. By establishing a Gibbs free energy phase diagram we trace the phase transition quantization to the discreteness of the layers' excess bend deformation energies in comparison to the thermal energy, even for this near room-temperature system. Monte Carlo simulations yielding spatially resolved nematic order parameters, density maps, and bond-orientational order parameters corroborate the universality and robustness of the confinement-induced columnar ring formation as well as its quantized nature.
A. W. Z. and M. G. M. gratefully acknowledge the Max Planck Society for funding, and the Deutsche Forschungsgemeinschaft (SFB 937, project A20) for support. A. V. K. acknowledges funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 778156. The German Science Foundation contributed by the Project No. SCHO 470/21-1 and HU 850/5-1 “Discotic Liquid Crystals in Nanoporous Solids: From the Structure and Dynamicsto Local Charge Transport.”P. H. and K. S. profited from the support within the Collaborative Research Initiative SFB 986, Tailor-Made Multi-Scale Materials Systems, projects B7, Z3, Hamburg (Germany). We thank Deutsche Elektronen Synchrotron DESY, Hamburg for access to the beam line P08 of the PETRA III synchrotron.
- Mathematical Sciences