Sentker, K.; Zantop, A.W.; Lippmann, M.; Hofmann, T.; Seeck, O.H.; Kityk, A.V.; Yildirim, A.; Schönhals, A.; Mazza, M.G.; Huber, P.:
Quantized Self-Assembly of Discotic Rings in a Liquid Crystal Confined in Nanopores. Physical Review Letters 120 (2018), p. 067801/1-7
10.1103/PhysRevLett.120.067801
Open Access Version
Abstract:
Disklike molecules with aromatic cores spontaneously stack up in linear columns with high, onedimensional
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 bondorientational
order parameters corroborate the universality and robustness of the confinement-induced
columnar ring formation as well as its quantized nature.