Interconnected CoFe₂O₄–Polypyrrole Nanotubes as Anode Materials for High Performance Sodium Ion Batteries

CoFe₂O₄-coated polypyrrole (PPy) nanotubes (CFO-PPy-NTs) with three-dimensional (3-D) interconnected networks have been prepared through a simple hydrothermal method. The application has been also studied for sodium ion batteries (SIBs). The finely crystallized CoFe₂O₄ nanoparticles (around 5 nm in size) are uniformly grown on the PPy nanotubes. When tested as anode materials for SIBs, the CFO-PPy-NT electrode maintains a discharge capacity of 400 mA h g^–1 and a stable Coulombic efficiency of 98% after 200 cycles at 100 mA g^–1. Even at a higher current density of 1000 mA g^–1, the composite can still retain a discharge capacity of 220 mA h g^–1 after 2000 cycles. The superior electrochemical performance could be mainly ascribed to the uniform distribution of CoFe₂O₄ on the 3-D matrix of PPy interconnected nanotubes, which favors the diffusion of sodium ions and electronic transportation and also buffers the large volumetric expansion during charge/discharge. Thereby our study suggests that such CFO-PPy-NTs have great potential as an anode material for SIBs

Synthesis and Isomeric Characterization of Well-Defined 8‑Shaped Polystyrene Using Anionic Polymerization, Silicon Chloride Linking Chemistry, and Metathesis Ring Closure

A methodology to efficiently synthesize well-defined, 8-shaped polystyrene using anionic polymerization, silicon chloride linking chemistry, and metathesis ring closure has been developed, and the 8-shaped architecture was ascertained using the fragmentation pattern of the corresponding Ag⁺ adduct, acquired with tandem mass spectrometry. The 4-arm star precursor, 4-<i>star</i>-α-4-pentenyl­polystyrene, was formed by linking α-4-pentenyl­poly­(styryl)­lithium (PSLi) with 1,2-bis­(methyl­dichlorosilyl)­ethane and reacting the excess PSLi with 1,2-epoxybutane to facilitate purification. Ring closure of 4-<i>star</i>-α-4-pentenyl­polystyrene was carried out in dichloromethane under mild conditions using a Grubbs metathesis catalyst, bis­(tricyclohexyl­phosphine)­benzylidine ruthenium­(IV) chloride. Both the 4-arm star precursor and resulting 8-shaped polystyrene were characterized using SEC, NMR, and MALDI-ToF mass spectrometry (MS). Tandem mass spectrometry (MS²) was used for the first time to study the fragmentation pattern of 8-shaped polystyrene. The results confirmed the formation of the intra-silicon-linked, 8-shaped polystyrene isomer, but the observed spectra left open the possibility that the inter-silicon-linked, 8-shaped polystyrene isomer was also produced

Solid-State NMR Study of the Chain Trajectory and Crystallization Mechanism of Poly(l‑lactic acid) in Dilute Solution

The nucleation and growth mechanisms of semicrystalline polymers are a controversial topic in polymer science. In this work, we investigate the chain-folding pattern, packing structure, and crystal habits of poly­(l-lactic acid) (PLLA) with a relatively low molecular weight, ⟨<i>M</i>_w⟩ = 46K g/mol, and PDI = 1.4 in single crystals formed from dilute amyl acetate (AA) solution (0.05 or 0.005 wt %) at a crystallization temperature (<i>T</i>_c) of 90, 50, or ∼0 °C. The crystal habits drastically changed from a facet lozenge shape at <i>T</i>_c = 90 °C to dendrites at ∼0 °C, whereas the chains adopt a thermodynamically stable α packing structure at both 90 and 0 °C. Comparing the experimental and simulated ¹³C–¹³C double quantum (DQ) buildup curves of ¹³C-labeled PLLA chains in crystals blended with nonlabeled chains at a mixing ratio of 1:9 indicates that the PLLA chains fold adjacently in multiple rows when the <i>T</i>_c ranges from 90 to ∼0 °C. The results at different length scales suggest that (i) a majority of the chains self-fold in dilute solution and form baby nuclei (intramolecular nucleation) and (ii) the intermolecular aggregation process (secondary nucleation), which is dominated by kinetics, results in morphological differences

Anomalous Confinement Slows Surface Fluctuations of Star Polymer Melt Films

The unusually large film thickness at which confinement effects manifest themselves in surface fluctuations of unentangled four-arm star polymers has been defined using film thicknesses from 10<i>R</i>_g to 107<i>R</i>_g. For 15k four-arm star polystyrene (SPS), confinement appears at a thickness between 112 nm (40<i>R</i>_g) and 72 nm (26<i>R</i>_g), which is remarkably larger than the thicknesses at which confinement appears for unentangled 6k linear (<15 nm, <7<i>R</i>_g) and 6k and 14k cyclic (24 and 22 nm, respectively) polystyrenes. Data for 15k star films can be rationalized using a two-layer model with a 17 nm (6<i>R</i>_g) thick highly viscous layer at the substrate, which is significantly thicker than the 1<i>R</i>_g thick “irreversibly adsorbed” layer. For a 29 nm (10<i>R</i>_g) thick film, more striking confinement occurs due to the combined influence of both interfaces. These results underscore the extraordinary role long-chain branching plays in dictating surface fluctuations of thin films

Assembly of Multifunctional Ni₂P/NiS_0.66 Heterostructures and Their Superstructure for High Lithium and Sodium Anodic Performance

The combination of structure designs at the microscopic and macroscopic level can efficiently enable electrode materials with greatly enhanced lithium and sodium storage. In this paper, the construction of Ni₂P/NiS_0.66 heterostructures and their assembly into a superstructure at the nanoscale were successfully achieved by a facile and effective strategy. In the obtained superstructure, the Ni₂P/NiS_0.66 heterostructures are homogeneously coated with ultrathin carbon layers (HT-NPS@C) and, at the same time, assembled into a yolk–shell nanosphere. Upon evaluation as the anode materials for Li-ion batteries, the HT-NPS@C delivers a high reversible capacity of 430 mA h g^–1 after 200 cycles at 200 mA g^–1 and ultrastable cyclability with negligible capacity loss over 500 cycles. Furthermore, the coin-type full cell with the LiNi_1/3Co_1/3Mn_1/3O₂ (LNCMO) cathode and HT-NPS@C anode deliver a high specific capacity of 323.5 mA h g^–1 after 50 cycles at 0.3 A g^–1. Apart from an excellent performance as promising anode materials for LIBs (Li-ion batteries), the Na-ion batteries with HT-NPS@C sphere electrodes also manifest a remarkable electrochemical performance

Modifying Surface Fluctuations of Polymer Melt Films with Substrate Modification

Deposition of a plasma polymerized film on a silicon substrate substantially changes the fluctuations on the surface of a sufficiently thin melt polystyrene (PS) film atop the substrate. Surface fluctuation relaxation times measured with X-ray photon correlation spectroscopy (XPCS) for ca. 4<i>R</i>_<i>g</i> thick melt films of 131 kg/mol linear PS on hydrogen-passivated silicon (H–Si) and on a plasma polymer modified silicon wafer can both be described using a hydrodynamic continuum theory (HCT) that assumes the film is characterized throughout its depth by the bulk viscosity. However, when the film thickness is reduced to ∼3<i>R_g</i>, confinement effects are evident. The surface fluctuations are slower than predicted using the HCT, and the confinement effect for the PS on H–Si is larger than that for the PS on the plasma polymerized film. This deviation is due to a difference in the thicknesses of the strongly adsorbed layers at the substrate which are impacted by the substrate surface energy