Quantized self-assembly of discotic rings in a liquid crystal confined in nanopores

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-forientational order parameters corroborate the universality and robustness of the confinement-induced columnar ring formation as well as its quantized nature.

Subjects

Soft Condensed Matter

Mesoscopic Systems and Quantum Hall Effect

Materials Science

Statistical Mechanics

Chemical Physics

DDC Class

620: Ingenieurwissenschaften

Funding(s)

Diskotische Flüssigkristalle in Nanoporösen Festkörpern: Von der Struktur und Dynamik zum lokalen Ladungtransport

Lizenz

https://creativecommons.org/licenses/by/4.0/

Name

PhysRevLett.120.067801.pdf

Size

1.78 MB

Format

Adobe PDF

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Quantized self-assembly of discotic rings in a liquid crystal confined in nanopores