Membranes incorporating zwitterionic chemistries have recently emerged as promising candidates for facilitating challenging ion–ion separations. Transport of ions in such membranes predominantly ...occurs in hydrated nanopores lined with zwitterionic monomers. To shed light on the physics of ion–ion selectivity underlying such materials, we conducted molecular dynamics simulations of sodium halide transport in model nanopores grafted with sulfobetaine methacrylate molecules. Our results reveal that in both functionalized and unfunctionalized nanopores smaller ions prefer to reside near the pore center, while the larger ions tend to reside near the pore walls. An enhancement in the selective transport of larger anions is observed within the unfunctionalized nanopores relative to that in salt-in-water solutions. Upon functionalization of the nanopores with zwitterions (ZIs), the disparities in the anionic distribution profiles within the pores coupled with differences in the anion-ZI interactions result in a slowdown of larger anions relative to smaller anions. Increasing the ZI grafting density exacerbates these effects, further promoting the selective transport of smaller anions. Our results suggest that selectivity toward large anions can be realized by using nanoporous membranes with ZI content that is high enough to facilitate ion/water partitioning into the pores while preserving the characteristic tendency of the unfunctionalized pores to facilitate faster transport of the larger anions. On the other hand, selectivity toward smaller anions can be achieved by targeting ZI content within the pores that is high enough to significantly slow down the transport of large anions but not high enough to hinder the partitioning of ions/water molecules into the pore due to steric effects.
Ni-rich cathodes have emerged as one of the most promising candidates for power next generation electric vehicles. However, they often suffer from poor capacity retention when charged to high ...voltages and the origin of this degradation remains elusive. Here, by using high throughput
operando
neutron diffraction, a universal four-stage structural evolution of Ni-rich cathodes is revealed during the initial cycle for the first time. Particularly, we discovered a universal structural transition in Ni-rich cathodes at ∼75% delithiation irrespective of Ni or substituent contents. This transition is hallmarked by the anomalous increase of average TM-O bond lengths, contradicting the conventional wisdom that TM-O bond lengths decrease during charge (oxidation). This anomaly is induced by the direct oxidation of lattice oxygen ions, which is rooted in the drastic decrease of oxygen-to-TM charge transfer gap at high degrees of delithiation. The onset of this anomalous transition matches very well with the onset of oxygen gas release and severe decline of capacity retention in Ni-rich cathodes, suggesting that this bulk structural transition plays an indispensable role in the degradation process. These findings shed light on the elusive degradation mechanism of Ni-rich cathodes, providing valuable clues to stabilize oxidized oxygen ions for stable cycling of layered oxide cathodes at high voltages.
A universal four-stage structural evolution mechanism of Ni-rich cathodes is revealed by high throughput
in situ
neutron diffraction. An anomalous increase of average TM-O bond distances is observed when more than ~75% Li
+
are removed.
MDM2 and MDMX, negative regulators of the tumor suppressor p53, can work separately and as a heteromeric complex to restrain p53's functions. MDM2 also has pro-oncogenic roles in cells, tissues, and ...animals that are independent of p53. There is less information available about p53-independent roles of MDMX or the MDM2-MDMX complex. We found that MDM2 and MDMX facilitate ferroptosis in cells with or without p53. Using small molecules, RNA interference reagents, and mutant forms of MDMX, we found that MDM2 and MDMX, likely working in part as a complex, normally facilitate ferroptotic death. We observed that MDM2 and MDMX alter the lipid profile of cells to favor ferroptosis. Inhibition of MDM2 or MDMX leads to increased levels of FSP1 protein and a consequent increase in the levels of coenzyme Q
, an endogenous lipophilic antioxidant. This suggests that MDM2 and MDMX normally prevent cells from mounting an adequate defense against lipid peroxidation and thereby promote ferroptosis. Moreover, we found that PPARα activity is essential for MDM2 and MDMX to promote ferroptosis, suggesting that the MDM2-MDMX complex regulates lipids through altering PPARα activity. These findings reveal the complexity of cellular responses to MDM2 and MDMX and suggest that MDM2-MDMX inhibition might be useful for preventing degenerative diseases involving ferroptosis. Furthermore, they suggest that MDM2/MDMX amplification may predict sensitivity of some cancers to ferroptosis inducers.
The simultaneous use of nonequilibrium reaction processing and complex macromolecular architecture is an exciting way to achieve nanostructures that are not easily accessible via standard static ...block polymer self-assembly. Previous work has shown that the polymerization of styrene in the presence of a poly(styrene)-block-poly(butadiene) (PS-PBD) diblock copolymer induces a nanostructural transition from a lamellar (LAM) to a hexagonally packed cylinder (HEX) morphology. The transition was found to be driven by in situ PS grafting from the PBD block, which transforms the PS-PBD coil–coil diblock copolymer to a poly(styrene)-block-poly(butadiene)-graft-poly(styrene) (PS-b-PBD-g-PS) coil–comb block polymer. In situ small-angle X-ray scattering and oscillatory shear dynamic mechanical spectroscopy measurements show that the order–order transition is not a simple epitaxial transition seen in prototypical block polymers, but undergoes a complex phase path in which the starting LAM phase at room temperature before polymerization initially disorders at elevated temperatures, evolves from a disordered phase to what is presumed to be a hexagonally perforated lamellae phase during the polymerization, and then transitions to a HEX phase on cooling to room temperature. The high-temperature phase persists for extended periods of time during the polymerization process, which allows for both the trapping and the characterization of the structure at room temperature. By utilizing nonequilibrium reactive processing to convert linear block copolymers to comb–coil type polymers, the creation of polymers with complex molecular topologies can be synthetically simplified while simultaneously allowing for the development of new processing modalities.
Lithium is widely used in contemporary energy applications, but its isolation from natural reserves is plagued by time-consuming and costly processes. While polymer membranes could, in principle, ...circumvent these challenges by efficiently extracting lithium from aqueous solutions, they usually exhibit poor ion-specific selectivity. Toward this end, we have incorporated host-guest interactions into a tunable polynorbornene network by copolymerizing 1) 12-crown-4 ligands to impart ion selectivity, 2) poly(ethylene oxide) side chains to control water content, and 3) a crosslinker to form robust solids at room temperature. Single salt transport measurements indicate these materials exhibit unprecedented reverse permeability selectivity (∼2.3) for LiCl over NaCl-the highest documented to date for a dense, water-swollen polymer. As demonstrated by molecular dynamics simulations, this behavior originates from the ability of 12-crown-4 to bind Na
ions more strongly than Li
in an aqueous environment, which reduces Na
mobility (relative to Li
) and offsets the increase in Na
solubility due to binding with crown ethers. Under mixed salt conditions, 12-crown-4 functionalized membranes showed identical solubility selectivity relative to single salt conditions; however, the permeability and diffusivity selectivity of LiCl over NaCl decreased, presumably due to flux coupling. These results reveal insights for designing advanced membranes with solute-specific selectivity by utilizing host-guest interactions.
The local atomic structure of SnSe was characterized across its orthorhombic-to-orthorhombic structural phase transition using x-ray pair distribution function analysis. Substantial Sn displacements ...with a dipolar character persist in the high-symmetry high-temperature phase, albeit with a symmetry different from that of the ordered displacements below the transition. The analysis implies that the transition is neither order-disorder nor displacive but rather a complex crossover. Robust ferrocoupled SnSe intralayer distortions suggest a ferroelectriclike instability as the driving force. These local symmetry-lowering Sn displacements are likely integral to the ultralow lattice thermal conductivity mechanism in SnSe.
Recent experiments have revealed that random zwitterionic amphiphilic copolymer (r-ZAC) membranes exhibit excellent Cl–/F– permselectivity circumventing the solubility-diffusivity trade-off. We ...conducted molecular dynamics simulations to investigate the origin of the experimental results on the transport of sodium halides in r-ZAC membranes. Our results indicate that the enhancement of Cl–/F– diffusivity selectivity in r-ZAC membranes (relative to that in bulk water) stems from the increase in dielectric drag dominating over the increase in Stokes drag, zwitterionic group-induced steric hindrance, and ion–polymer interactions. The importance of dielectric drag is further demonstrated by showing that reduction in ionic charges leads to a complete reversal of the diffusivity selectivity trends. We conclude that leveraging the impact of hydrophilic nanoconfinement on the dynamics of water can be utilized as a strategy to simultaneously augment solubility selectivity and diffusivity selectivity for separations, wherein the flux of the larger ionic species is desired over that of the smaller.
Fast charging (<15 min) of lithium‐ion batteries (LIBs) for electrical vehicles (EVs) is widely seen as the key factor that will greatly stimulate the EV markets, and its realization is mainly ...hindered by the sluggish diffusion of Li+. To have a mechanistic understanding of Li+ diffusion within LIBs, in this study, structural evolutions of electrodes for a Ni‐rich LiNi0.6Mn0.2Co0.2O2 (NMC622) || graphite cylindrical cell with high areal loading (2.78 mAh cm−2) are developed for operando neutron powder diffraction study at different charging rates. Via sequential Rietveld refinements, changes in structures of NMC622 and LixC6 are obtained during moderate and fast charging (from 0.27 C to 4.4 C). NMC622 exhibits the same structural evolution regardless of C‐rates. For phase transitions of LixC6, the stage I (LiC6) phase emerges earlier during the stepwise intercalation at a lower state of charge when charging rate is increased. It is also found that the stage II (LiC12) → stage I (LiC6) transition is the rate‐limiting step during fast charging. The LiC12 → LiC6 transition mechanism is further analyzed using the Johnson–Mehl–Avrami–Kolmogorov model. It is concluded as a diffusion‐controlled, 1D phase transition with decreasing nucleation kinetics under increasing chargingrates.
Operando neutron diffraction has been used to study the structural evolutions and phase transitions in a LiNi0.6Mn0.2Co0.2O2 (NMC622) || graphite cylindrical cell at different charging rates. The phase transition from LiC12 to LiC6 is a limiting step under fast charging, which is a diffusion‐controlled, 1D process with decreasing nucleation kinetics via the Johnson–Mehl–Avrami–Kolmogorov model.
Recently, a variety of “click” or other additive chemistries have been introduced to functionalize polymers after polymerization to target specific applications, for example, membranes, catalysis, or ...drug delivery systems. It is generally assumed that the inclusion of these “click” linking groups has minimal impact on the thermodynamics of the polymer as a whole. In this study, we demonstrate that the introduction of these click-derived units has a profound impact on the Flory–Huggins parameter of polyether derivatives. Using random phase approximation fits for small-angle X-ray scattering data from block copolymer pairs to estimate the Flory–Huggins interaction parameter (χ), we determined that poly(ethylene oxide) (PEO) and poly(allyl glycidyl ether) (PAGE), which differ only by the inclusion of an allyl sidechain, have a χ of 0.030 (at T = 34 °C). While PEO is miscible with poly(lactide) (PLA) at nearly all temperatures, the PLA/PAGE χ determined experimentally is 0.015 (at T = 30 °C). Atomistic molecular dynamics simulations of PEO/PAGE oligomer blends show that upon blending, PEO chains contract and move closer together, while PAGE chains stretch and spread apart, indicating an enthalpic contribution to the χ parameter due to changes in polymer coordination resulting from the conformational asymmetry of PAGE and PEO. These studies demonstrate the large impact that functionalization and side-chain units have on the χ parameter of polymer pairs.
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