Quantized Self-Assembly of Discotic Rings in a Liquid Crystal Confined in Nanopores

TL;DR

This study demonstrates that confining discotic liquid crystals in nanopores induces a reversible, quantized formation of concentric rings of bent columns, revealing new self-assembly behavior driven by confinement and energy quantization.

Contribution

It reveals a novel quantized self-assembly of discotic rings in nanopores, supported by experimental and simulation evidence, expanding understanding of confined liquid crystal behavior.

Findings

Reversible formation of concentric rings in nanopores.

Quantized layer-by-layer self-assembly driven by energy discreteness.

Agreement between experiments and Monte Carlo simulations.

Abstract

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.