4 research outputs found
Significant Enhancement of the Chiral Correlation Length in Nematic Liquid Crystals by Gold Nanoparticle Surfaces Featuring Axially Chiral Binaphthyl Ligands
Chirality
is a fundamental scientific concept best described by
the absence of mirror symmetry and the inability to superimpose an
object onto its mirror image by translation and rotation. Chirality
is expressed at almost all molecular levels, from single molecules
to supramolecular systems, and present virtually everywhere in nature.
Here, to explore how chirality propagates from a chiral nanoscale
surface, we study gold nanoparticles functionalized with axially chiral
binaphthyl molecules. In particular, we synthesized three enantiomeric
pairs of chiral ligand-capped gold nanoparticles differing in size,
curvature, and ligand density to tune the chirality transfer from
nanoscale solid surfaces to a bulk anisotropic liquid crystal medium.
Ultimately, we are examining how far the chirality from a nanoparticle
surface reaches into a bulk material. Circular dichroism spectra of
the gold nanoparticles decorated with binaphthyl thiols confirmed
that the binaphthyl moieties form a cisoid conformation in isotropic
organic solvents. In the chiral nematic liquid crystal phase, induced
by dispersing the gold nanoparticles into an achiral anisotropic nematic
liquid crystal solvent, the binaphthyl moieties on the nanoparticle
surface form a transoid conformation as determined by imaging the
helical twist direction of the induced cholesteric phase. This suggests
that the ligand density on the nanoscale metal surfaces provides a
dynamic space to alter and adjust the helicity of binaphthyl derivatives
in response to the ordering of the surrounding medium. The helical
pitch values of the induced chiral nematic phase were determined,
and the helical twisting power (HTP) of the chiral gold nanoparticles
calculated to elucidate the chirality transfer efficiency of the binaphthyl
ligand capped gold nanoparticles. Remarkably, the HTP increases with
increasing diameter of the particles, that is, the efficiency of the
chirality transfer of the binaphthyl units bound to the nanoparticle
surface is diminished as the size of the particle is reduced. However,
in comparison to the free ligands, per chiral molecule all tested
gold nanoparticles induce helical distortions in a 10- to 50-fold
larger number of liquid crystal host molecules surrounding each particle,
indicating a significantly enhanced chiral correlation length. We
propose that both the helicity and the chirality transfer efficiency
of axially chiral binaphthyl derivatives can be controlled at metal
nanoparticle surfaces by adjusting the particle size and curvature
as well as the number and density of the chiral ligands to ultimately
measure and tune the chiral correlation length
Non-electronic gas sensors from electrospun mats of liquid crystal core fibres for detecting volatile organic compounds at room temperature
<p>Non-woven mats comprised of liquid crystal-functionalised fibres are coaxially electrospun to create soft gas sensors that function non-electronically, thus requiring no power supply, detecting organic vapours at room temperature. The fibres consist of a poly(vinylpyrrolidone) (PVP) sheath surrounding a core of nematic 4-cyano-4ʹpentylbiphenyl (5CB) liquid crystal. Several types of mats, containing uniformly cylindrical or irregular beaded fibres, in uniform or random orientations, are exposed to toluene vapour as a representative volatile organic compound. Between crossed polarisers all mats respond with a fast (response time on the order of a second or faster) reduction in brightness during gas exposure, and they return to the original state upon removal of the gas almost as quickly. With beaded fibres, the response of the mats is visible even without polarisers. We discuss how variations in fibre spinning conditions such as humidity level and the ratio of core-sheath fluid flow rates can be used to tune fibre morphology and thereby the response. Considering future development perspectives, we argue that fibres turned responsive through the incorporation of a liquid crystal core show promise as a new generation of sensors with textile form factor, ideal for wearable technology applications.</p
Detecting, Visualizing, and Measuring Gold Nanoparticle Chirality Using Helical Pitch Measurements in Nematic Liquid Crystal Phases
Chirality at the nanoscale, or more precisely, the chirality or chiroptical effects of chiral ligand-capped metal nanoparticles (NPs) is an intriguing and rapidly evolving field in nanomaterial research with promising applications in catalysis, metamaterials, and chiral sensing. The aim of this work was to seek out a system that not only allows the detection and understanding of NP chirality but also permits visualization of the extent of chirality transfer to a surrounding medium. The nematic liquid crystal phase is an ideal candidate, displaying characteristic defect texture changes upon doping with chiral additives. To test this, we synthesized chiral cholesterol-capped gold NPs and prepared well-dispersed mixtures in two nematic liquid crystal hosts. Induced circular dichroism spectropolarimetry and polarized light optical microscopy revealed that all three gold NPs induce chiral nematic phases, and that those synthesized in the presence of a chiral bias (disulfide) are more powerful chiral inducers than those where the NP was formed in the absence of a chiral bias (prepared by conjugation of a chiral silane to preformed NPs). Helical pitch data here visually show a clear dependence on the NP size and the number of chiral ligands bound to the NP surface, thereby supporting earlier experimental and theoretical data that smaller metal NPs made in the presence of a chiral bias are stronger chiral inducers
Biocompatible 3D Liquid Crystal Elastomer Cell Scaffolds and Foams with Primary and Secondary Porous Architecture
3D
biodegradable and highly regular foamlike cell scaffolds based
on biocompatible side-chain liquid crystal elastomers have been prepared.
Scaffolds with a primary porosity characterized by spatially interlaced,
interconnected microchannels or an additional secondary porosity featuring
interconnected microchannel networks define the novel elastomeric
scaffolds. The macroscale
morphology of the dual porosity 3D scaffold resembles vascular networks
observed in tissue. 3D elastomer foams show four times higher cell
proliferation capability compared to conventional porous templated
films and within the channels guide spontaneous cell alignment enabling
the possibility of tissue construct fabrication toward more clinically
complex environments