4 research outputs found
Filaments with Affinity Binding and Wet Strength Can Be Achieved by Spinning Bifunctional Cellulose Nanofibrils
We
demonstrate benzophenone (BP) conjugation via amine-reactive
esters onto oxidized cellulosic fibers that were used as precursors,
after microfluidization, of photoactive cellulose nanofibrils (CNF).
From these fibrils, cellulose I filaments were synthesized by hydrogel
spinning in an antisolvent followed by fast biradical UV cross-linking.
As a result, the wet BP-CNF filaments retained extensively the original
dry strength (a remarkable ∼80% retention). Thus, the principal
limitation of these emerging materials was overcome (the wet tensile
strength is typically <0.5% of the value measured in dry conditions).
Subsequently, antihuman hemoglobin (anti-Hb) antibodies were conjugated
onto residual surface carboxyl groups, making the filaments bifunctional
for their active groups and properties (wet strength and bioactivity).
Optical (surface plasmon resonance) and electroacoustic (quartz crystal
microgravimetry) measurements conducted with the bifunctional CNF
indicated effective anti-Hb conjugation (2.4 mg m<sup>–2</sup>), endowing an excellent sensitivity toward Hb targets (1.7 ±
0.12 mg m<sup>–2</sup>) and negligible nonspecific binding.
Thus, the anti-Hb biointerface was deployed on filaments that captured
Hb efficiently from aqueous matrices (confocal laser microscopy of
FITC-labeled antibodies). Significantly, the anti-Hb biointerface
was suitable for regeneration, while its sensitivity and selectivity
in affinity binding can be tailored by application of blocking copolymers.
The developed bifunctional filaments based on nanocellulose offer
great promise in detection and affinity binding built upon 1D systems,
which can be engineered into other structures for rational use of
material and space
Adsorption Behavior of Perfluorinated Sulfonic Acid Ionomer on Highly Graphitized Carbon Nanofibers and Their Thermal Stabilities
A systematic
adsorption study of perfluorinated sulfonic acid Nafion ionomer on
ribbon-type highly graphitized carbon nanofibers (CNFs) was carried
out using fluorine-19 nuclear magnetic resonance spectroscopy. On
the basis of the values obtained for the equilibrium constant (<i>K</i><sub>eq </sub>, derived from Langmuir isotherm), the
ionomer has varying affinities for CNFs (<i>K</i><sub>eq </sub>between 5 and 22) as compared to Vulcan (<i>K</i><sub>eq </sub> = 18), depending on surface treatments. However, the interactions
are most likely governed by different adsorption mechanisms depending
on hydrophilicity/hydrophobicity of the adsorbent carbon. The ionomer
is probably adsorbed via the polar sulfonic group on hydrophilic Vulcan,
whereas it is adsorbed primarily via hydrophobic −CF<sub>2</sub>– backbone on the highly hydrophobic pristine CNFs. Ionomer
adsorption behavior is gradually altered from apolar to polar group
adsorption for the acid-modified CNFs of decreasing hydrophobicity.
This is indicated by the initial decrease and then increase in the
value of <i>K</i><sub>eq </sub>with the increasing
strength of the acid treatment. The corresponding carbon–ionomer
composite also showed varying thermal stability depending on Nafion
orientation. The specific maximum surface coverage (Γ<sub>Smax</sub>) of the CNFs is 1 order of magnitude higher than that of Vulcan.
The large discrepancy is due to the fact that the ionomers are inaccessible
to the internal surface area of Vulcan with high microporosity
High-Throughput Synthesis of Lignin Particles (∼30 nm to ∼2 μm) via Aerosol Flow Reactor: Size Fractionation and Utilization in Pickering Emulsions
An
aerosol flow reactor was used for the first time for high-throughput,
high yield synthesis of spherical lignin particles with given inherent
hydrophilicity, depending on the precursor biomolecule. In situ fractionation
via Berner type impactor afforded populations with characteristic
sizes ranging from ∼30 nm to 2 μm. The as-produced, dry
lignin particles displayed excellent mechanical integrity, even after
redispersion under high shear in either mineral oil or water. They
were effective in the stabilization of oil-in-water (O/W) Pickering
emulsions with tunable droplet size, depending on the dimension of
the lignin particles used for emulsification. The emulsion stability
correlated with particle concentration as well as the respective lignin
type. For the O/W emulsions stabilized with the more hydrophilic lignin
particles, negligible changes in phase separation via Ostwald ripening
and coalescence were observed over a period of time of more than two
months. Together with the fact that the lignin particle concentrations
used in emulsification were as low as 0.1%, our results reveal a remarkable
ability to endow emulsified systems with high colloidal stability.
Overall, we offer a new, high-yield, scalable nanomanufacturing approach
to producing dry spherical lignin particles with size control and
high production capacity. A number of emerging applications for these
organic particles can be envisioned and, as a proof-of-concept, we
illustrate here surfactant-free emulsification
Formulation and Composition Effects in Phase Transitions of Emulsions Costabilized by Cellulose Nanofibrils and an Ionic Surfactant
Cellulose nanofibrils
(CNF) offer great prospects as a natural
stabilizer of colloidal dispersions and complex fluids for application
in food, pharma, and cosmetics. In this study, an ionic surfactant
(sodium dodecyl sulfate, SDS) was used as emulsifier of oil-in-water
and water-in-oil emulsions that were further costabilized by addition
of CNF. The adsorption properties of SDS in both, CNF dispersions
and emulsions, as well as the influence of composition (CNF and SDS
concentration) and formulation (ionic strength, oil, and CNF types)
on the phase behavior were elucidated and described in the framework
of Windsor systems. At low salinity, the phase transition of emulsions
containing CNF and SDS at low concentrations was controlled by molecular
transfer in the oil-in-water system. Irregular droplets and “bi-continuous”
morphologies were observed at medium and high salinity for systems
containing high CNF and SDS concentrations. Water-in-oil emulsions
were only possible at high salinity and SDS concentrations in the
presence of small amounts of CNF. The results revealed some subtle
differences in CNF interfacial activity, depending on the method used
for their isolation via fiber deconstruction, either from microfluidization
or aqueous counter collision. Overall, we propose that the control
of emulsion morphology and stability by addition of CNF opens the
possibility of developing environmentally friendly complex systems
that display high stability and respond to ionic strength following
the expectations of classical emulsion systems