How do ionic superdiscs self-assemble in nanopores?

• Main Authors: Li, Zhuoqing, Raab, Aileen R, Kolmangadi, Mohamed A, Busch, Mark, Grunwald, Marco, Demel, Felix, Bertram, Florian, Kityk, Andriy V, Schoenhals, Andreas, Laschat, Sabine, Huber, Patrick
• Format: Journal Article
• Language: English
• Published: 23-01-2024
• Subjects: Physics - Applied Physics; Physics - Chemical Physics; Physics - Materials Science; Physics - Mesoscale and Nanoscale Physics; Physics - Soft Condensed Matter
• DOI: 10.48550/arxiv.2401.12663

Discotic ionic liquid crystals (DILCs) consist of self-assembled superdiscs
of cations and anions that spontaneously stack in linear columns with high
one-dimensional ionic and electronic charge mobility, making them prominent
model systems for functional soft matter. Unfortunately, a homogeneous
alignment of DILCs on the macroscale is often not achievable, which
significantly limits their applicability. Infiltration into nanoporous solid
scaffolds can in principle overcome this drawback. However, due to the extreme
experimental challenges to scrutinise liquid crystalline order in extreme
spatial confinement, little is known about the structures of DILCs in
nanopores. Here, we present temperature-dependent high-resolution optical
birefringence measurement and 3D reciprocal space mapping based on
synchrotron-based X-ray scattering to investigate the thermotropic phase
behaviour of dopamine-based ionic liquid crystals confined in cylindrical
channels of 180~nm diameter in macroscopic anodic aluminum oxide (AAO)
membranes. As a function of the membranes' hydrophilicity and thus the
molecular anchoring to the pore walls (edge-on or face-on) and the variation of
the hydrophilic-hydrophobic balance between the aromatic cores and the alkyl
side chain motifs of the superdiscs by tailored chemical synthesis, we find a
particularly rich phase behaviour, which is not present in the bulk state. It
is governed by a complex interplay of liquid crystalline elastic energies
(bending and splay deformations), polar interactions and pure geometric
confinement, and includes textural transitions between radial and axial
alignment of the columns with respect to the long nanochannel axis.