2 research outputs found
Stereochemical Control of Nonamphiphilic Lyotropic Liquid Crystals: Chiral Nematic Phase of Assemblies Separated by Six Nanometers of Aqueous Solvents
Unlike conventional thermotropic
and lyotropic liquid crystals,
nonamphiphilic lyotropic liquid crystals consist of hydrated assemblies
of nonamphiphilic molecules that are aligned with a separation of
about 6 nm between assemblies in an aqueous environment. This separation
raises the question of how chirality, either from chiral mesogens
or chiral dopants, would impact the phase as the assemblies that need
to interact with each other are about 6 nm apart. Here, we report
the synthesis of three stereoisomers of disodium chromonyl carboxylate,
5′DSCG-diviol, and the correlation between the molecular structure,
bulk assembly, and liquid crystal formation. We observed that the
chiral isomers (enantiomers 5′DSCG-(<i>R,R</i>)-diviol
and 5′DSCG-(<i>S,S</i>)-diviol) formed liquid crystals
while the achiral isomer 5′DSCG-<i>meso</i>-diviol
did not. Circular dichroism indicated a chiral conformation with bisignate
cotton effect. The nuclear Overhauser effect in proton NMR spectroscopy
revealed conformations that are responsible for liquid crystal formation.
Cryogenic transmission electron microscopy showed that chiral 5′DSCG-diviols
form assemblies with crossings. Interestingly, only planar alignment
of the chiral nematic phase was observed in liquid crystal cells with
thin spacers. The homeotropic alignment that permitted a fingerprint
texture was obtained only when the thickness of the liquid crystal
cell was increase to above ∼500 μm. These studies suggest
that hydrated assemblies of chiral 5′DSCG-diviol can interact
with each other across a 6 nm separation in an aqueous environment
by having a twist angle of about 0.22° throughout the sample
between the neighboring assemblies
Novel Surface Molecular Functionalization Route To Enhance Environmental Stability of Tellurium-Containing 2D Layers
Recent
studies have shown that tellurium-based two-dimensional
(2D) crystals undergo dramatic structural, physical, and chemical
changes under ambient conditions, which adversely impact their much
desired properties. Here, we introduce a diazonium molecule functionalization-based
surface engineering route that greatly enhances their environmental
stability without sacrificing their much desired properties. Spectroscopy
and microscopy results show that diazonium groups significantly slow
down the surface reactions, and consequently, gallium telluride (GaTe),
zirconium telluride (ZrTe<sub>3</sub>), and molybdenum ditelluride
(MoTe<sub>2</sub>) gain strong resistance to surface transformation
in air or when immersed under water. Density functional theory calculations
show that functionalizing molecules reduce surface reactivity of Te-containing
2D surfaces by chemical binding followed by an electron withdrawal
process. While pristine surfaces structurally decompose because of
strong reactivity of Te surface atoms, passivated functionalized surfaces
retain their structural anisotropy, optical band gap, and emission
characteristics as evidenced by our conductive atomic force microscopy,
photoluminescence, and absorption spectroscopy measurements. Overall,
our findings offer an effective method to increase the stability of
these environmentally sensitive materials without impacting much of
their physical properties