3 research outputs found
Dielectric Characterization of Confined Water in Chiral Cellulose Nanocrystal Films
A known
deterrent to the large-scale development and use of cellulose
nanocrystals (CNCs) in composite materials is their affinity for moisture,
which has a profound effect on dispersion, wetting, interfacial adhesion,
matrix crystallization, water uptake, and hydrothermal stability.
To quantify and control the hydration and confinement of absorbed
water in CNCs, we studied sulfated-CNCs neutralized with sodium cations
and CNCs functionalized with less hydrophilic methylÂ(triphenyl)Âphosphonium
cations. Films were cast from water suspensions at 20 °C under
controlled humidity and drying rate, yielding CNC materials with distinguishably
different dielectric properties and cholesteric structures. By controlling
the evaporation rate, we obtained self-assembled chiral CNC films
with extended uniformity, having helical modulation length (nominal
pitch) tunable from 1300 to 600 nm. SEM imaging and UV–vis–NIR
total reflectance spectra revealed tighter and more uniform CNC packing
in films cast at slow evaporation rates or having lower surface energy
when modified with phosphonium. The dielectric constant was measured
by a noncontact microwave cavity perturbation method and fitted to
a classical mixing model employing randomly oriented ellipsoidal water
inclusions. The dielectric constant of absorbed water was found to
be significantly smaller than that for free liquid indicating a limited
mobility due to binding with the CNC “matrix”. In the
case of hydrophilic Na-modified CNCs, a decreasing pitch led to greater
anisotropy in the shape of moisture inclusions (ellipsoidal to platelet-like)
and greater confinement. In contrast, the structure of hydrophobic
phosphonium-modified CNC films was found to have reduced pitch, yet
the shape of confined water remained predominantly spherical. These
results provide a useful perspective on the current state of understanding
of CNC–water interactions as well as on CNC self-assembly mechanisms.
More broadly, we believe that our results are beneficial for the realization
of CNC-based functional materials and composites
Correction to “Simultaneously Tailoring Surface Energies and Thermal Stabilities of Cellulose Nanocrystals Using Ion Exchange: Effects on Polymer Composites Properties for Transportation, Infrastructure, and Renewable Energy Applications”
Correction
to “Simultaneously Tailoring Surface
Energies and Thermal Stabilities of Cellulose Nanocrystals Using Ion
Exchange: Effects on Polymer Composites Properties for Transportation,
Infrastructure, and Renewable Energy Applications
Probing the Mycobacterial Trehalome with Bioorthogonal Chemistry
Mycobacteria, including the pathogen <i>Mycobacterium
tuberculosis</i>, use the non-mammalian disaccharide trehalose
as a precursor for
essential cell-wall glycolipids and other metabolites. Here we describe
a strategy for exploiting trehalose metabolic pathways to label glycolipids
in mycobacteria with azide-modified trehalose (TreAz) analogues. Subsequent
bioorthogonal ligation with alkyne-functionalized probes enabled detection
and visualization of cell-surface glycolipids. Characterization of
the metabolic fates of four TreAz analogues revealed unique labeling
routes that can be harnessed for pathway-targeted investigation of
the mycobacterial trehalome