7 research outputs found
Multiple Feeding Strategy for Phase Transformation of GMP in Continuous Couette–Taylor Crystallizer
A continuous Couette–Taylor (CT) crystallizer
with a multiple
feed mode was developed to promote the phase transformation of guanosine
5-monophosphate (GMP). In drowning-out crystallization, amorphous
GMP is initially precipitated and then transformed into hydrate GMP
crystals via the spontaneous nucleation of hydrate crystals and consecutive
dissolution of the amorphous GMP and growth of hydrate GMP crystals.
Importantly, the multiple feeding strategy had a significant accelerating
effect on the phase transformation process, resulting in the complete
conversion of the amorphous GMP into hydrate crystals within an overall
mean residence time of 2.5 min, even with a high GMP feed concentration
of 152.8 g/L and low rotation speed of 300 rpm. Thus, the phase transformation
in the continuous CT crystallizer with the multiple feed mode (feeding
mode IV) was at least 2 times faster than the phase transformation
with the conventional feeding mode (feeding mode I), and 10 times
faster when compared to the phase transformation in a continuous MSMPR
crystallizer. The effectiveness of the multiple feeding mode for the
phase transformation can be explained in terms of independently controlling
the supersaturation, mean residence time, seeding effect, and mass
transfer rates in each region of CT crystallizer depending on the
multiple feeding strategy and feeding distribution ratio
Role of Nanoparticle Selectivity in the Symmetry Breaking of Cylindrically Confined Block Copolymers
We have comprehensively studied the
effect of nanoparticle selectivity
on the self-assembly of symmetrical block copolymer (BCP) under cylindrical
confinement using simulation and experiment. For the simulation, a
coarse-grained molecular dynamics (CGMD) simulation has been utilized,
and we investigated the confined assembly using nanoparticles with
three different interactions with block copolymer: (i) neutral to
both <i>A</i> (wall-attractive) and <i>B</i> (wall-repulsive)
phases, (ii) <i>B</i> domain selective, and (iii) <i>A</i> domain selective. It is predicted that nonselective (neutral)
nanoparticles (NPs) tend to be placed near the interface between radially
alternating layers of <i>A</i> or <i>B</i> domains,
while selective (<i>A</i> or <i>B</i>) NPs swell
the corresponding phase, inducing discrete asymmetrical morphologies.
We also find that pure asymmetrical BCP forms more radially perforated
morphologies, while symmetrical BCP/NP forms more discrete morphologies.
Experimentally, we have incorporated gold or magnetite NPs with the
matching three types of selectivity toward symmetrical diblock PS-<i>b</i>-PI and electrospun them. The morphologies observed from
our study have been quantified by morphological classification numbers
to identify the degree of asymmetry formed. The qualitative and quantitative
comparisons between experiment and simulation confirm the validity
of the simulation tool and shed light on the NP’s role on breaking
the symmetry of BCP under cylindrical confinement
Enhanced Dispersion and Stability of Petroleum Coke Water Slurries via Triblock Copolymer and Xanthan Gum: Rheological and Adsorption Studies
The rheology of petroleum coke (petcoke)
water slurries was investigated
with a variety of nonionic and anionic dispersants including polyÂ(ethylene
oxide) (PEO)-<i>b</i>-polyÂ(propylene oxide) (PPO)-<i>b</i>-PEO triblock copolymers (trade name: Pluronic, BASF),
polyÂ(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), polyÂ(ethylene
oxide) (PEO), polyÂ(carboxylate acid) (PCA), sodium lignosulfonate
(SLS), and polyÂ(acrylic acid) (PAA). Each effective dispersant system
shared very similar rheological behavior to the others when examined
at the same volume fraction from its maximum petcoke loading. Triblock
copolymer, Pluronic F127 (F127), was found to be the best dispersant
by comparing the maximum petcoke loading for each dispersant. The
yield stress was measured as a function of petcoke loading and dispersant
concentration for F127, and a minimum dispersant concentration was
observed. An adsorption isotherm and atomic force microscopy (AFM)
images reveal that this effective dispersion of petcoke particles
by F127 is due to the formation of a uniform monolayer of brushes
where hydrophobic PPO domains of F127 adhere to the petcoke surface,
while hydrophilic PEO tails fill the gap between petcoke particles.
F127 was then compared to other Pluronics with various PEO and PPO
chain lengths, and the effects of surface and dispersant hydrophilicity
were examined. Finally, xanthan gum (XG) was tested as a stabilizer
in combination with F127 for potential industrial application, and
F127 appears to break the XG aggregates into smaller aggregates through
competitive adsorption, leading to an excellent degree of dispersion
but the reduced stability of petcoke slurries
Preparation and Characterization of Amphiphilic Triblock Terpolymer-Based Nanofibers as Antifouling Biomaterials
Antifouling surfaces are critical for the good performance
of functional
materials in various applications including water filtration, medical
implants, and biosensors. In this study, we synthesized amphiphilic
triblock terpolymers (tri-BCPs, coded as KB) and fabricated amphiphilic
nanofibers by electrospinning of solutions prepared by mixing the
KB with polyÂ(lactic acid) (PLA) polymer. The resulting fibers with
amphiphilic polymer groups exhibited superior antifouling performance
to the fibers without such groups. The adsorption of bovine serum
albumin (BSA) on the amphiphilic fibers was about 10-fold less than
that on the control surfaces from PLA and PET fibers. With the increase
of the KB content in the amphiphilic fibers, the resistance to adsorption
of BSA was increased. BSA was released more easily from the surface
of the amphiphilic fibers than from the surface of hydrophobic PLA
or PET fibers. We have also investigated the structural conformation
of KB in fibers before and after annealing by contact angle measurements,
transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy
(EDX), and coarse-grained molecular dynamics (CGMD) simulation to
probe the effect of amphiphilic chain conformation on antifouling.
The results reveal that the amphiphilic KB was evenly distributed
within as-spun hybrid fibers, while migrated toward the core from
the fiber surface during thermal treatment, leading to the reduction
in antifouling. This suggests that the antifouling effect of the amphiphilic
fibers is greatly influenced by the arrangement of amphiphilic groups
in the fibers
Zwitterionic Polymer Gradient Interphases for Reversible Zinc Electrochemistry in Aqueous Alkaline Electrolytes
Aqueous alkaline zinc batteries are of scientific and
technological
interest because of the potential they offer for cost-effective and
safe storage of electrical energy. Poor electrochemical reversibility
and shape change of the Zn anode, propensity of Zn to become passivated
by surface oxides and hydroxide films upon prolonged exposure to the
electrolyte, and electroreduction of water are well-studied but remain
unsolved challenges. Here, we create and study electrochemical and
transport properties of precise, spatially tunable zwitterionic polymer
interphases grown directly on Zn using an initiated-chemical vapor
deposition polymerization methodology. In aqueous alkaline media,
spatial gradients in compositionfrom the polymer–electrolyte
interface to the solid–polymer interfacepromote highly
reversible redox reactions at high current density (20 mA cm–2) and high areal capacity (10 mAh cm–2). Via molecular dynamics and experimental analyses, we conclude
that the interphases function by regulating the distribution and activity
of interfacial water molecules, which simultaneously enables fast
ion transport and suppression of surface passivation and the hydrogen
evolution reaction. To illustrate the practical relevance of our findings,
we study aqueous Zn||NiOOH and Zn||air batteries and observe that
zwitterionic polymer interphases produce extended life at high currents
and high areal capacity
Harvesting Interconductivity and Intraconductivity of Graphene Nanoribbons for a Directly Deposited, High-Rate Silicon-Based Anode for Li-Ion Batteries
Batteries for high-rate
applications such as electric vehicles need to be efficient at mobilizing
charges (both electrons and ions). To this end, choice of the conductive
carbon in the electrode can make a significant difference in the performance
of the electrode. In this work, graphene nanoribbons (GNRs) are explored
as conductive pathways for a silicon-based anode. Water-based electrospinning
is employed to directly deposit polyÂ(vinyl alcohol) (PVA)–silicon–graphene
nanoribbon composite fibers on a copper current collector. The size
of the employed GNRs dictates their placement: either inside each
fiber (small GNRs) or as a bridge between multiple fibers (large GNRs).
Galvanostatic charge/discharge cycles reveal that fibers with GNRs
have higher capacity and overall retention compared to those with
corresponding precursor carbon nanotubes (CNTs). To further distinguish
the effectiveness of GNRs as the conductive agent, samples with two
GNRs and their parent CNTs were subject to rate-capability tests.
Fibers with large GNR inclusions exhibit an excellent performance
at fast rates (1400 mAh g<sup>–1</sup> at 12.6 A g<sup>–1</sup>). For both pairs, enhancement in the performance of GNRs over CNTs
grows with increasing rates. Finally, a small amount of large GNRs
(1 wt %) is blended with small GNRs in the fibers to create synergy
between intra- and interconductivity provided by small and large GNRs,
respectively. The resulting fiber mat exhibits the same capacity as
that of only small GNRs, even at a current rate that is 4 times higher
(300 mAh g<sup>–1</sup> at 21 A g<sup>–1</sup>)
Adaptive Ion Channels Formed in Ultrathin and Semicrystalline Polymer Interphases for Stable Aqueous Batteries
Aqueous
Zn batteries have recently emerged as promising candidates
for large-scale energy storage, driven by the need for a safe and
cost-effective technology with sufficient energy density and readily
accessible electrode materials. However, the energy density and cycle
life of Zn batteries have been limited by inherent chemical, morphological,
and mechanical instabilities at the electrode–electrolyte interface
where uncontrolled reactions occur. To suppress the uncontrolled reactions,
we designed a crystalline polymer interphase for both electrodes,
which simultaneously promotes electrode reversibility via fast and
selective Zn transport through the adaptive formation of ion channels.
The interphase comprises an ultrathin layer of crystalline poly(1H,1H,2H,2H-perfluorodecyl acrylate), synthesized and applied as a conformal
coating in a single step using initiated chemical vapor deposition
(iCVD). Crystallinity is optimized to improve interphase stability
and Zn-ion transport. The optimized interphase enables a cycle life
of 9500 for Zn symmetric cells and over 11,000 for Zn-MnO2 full-cell batteries. We further demonstrate the generalizability
of this interphase design using Cu and Li as examples, improving their
stability and achieving reversible cycling in both. The iCVD method
and molecular design unlock the potential of highly reversible and
cost-effective aqueous batteries using earth-abundant Zn anode materials,
pointing to grid-scale energy storage