Caizhen Zhu

Mussel Inspired Modification of Polypropylene Separators by Catechol/Polyamine for Li-Ion Batteries

Inspired by the remarkable adhesion of mussel, dopamine, a mimicking adhesive molecule, has been widely used for surface modification of various materials ranging from organic to inorganic. However, dopamine and its derivatives are expensive which impede their application in large scale. Herein, we replaced dopamine with low-cost catechol and polyamine (only 8% of the cost of dopamine), which could be polymerized in an alkaline solution and deposited on the surfaces of various materials. By using this cheap and simple modification method, polypropylene (PP) separator could be transformed from hydrophobic to hydrophilic, while the pore structure and mechanical property of the separator remained intact. The uptake of electrolyte increased from 80% to 270% after the hydrophilic modification. Electrochemical studies demonstrated that battery with the modified PP separator had a better Coulombic efficiency (80.9% to 85.3%) during the first cycle at a current density of 0.1 C, while the discharging current density increased to 15 C and the discharge capacity increased by 1.4 times compared to the battery using the bare PP separator. Additionally, the modification allowed excellent stability during manifold cycles. This study provides new insights into utilizing low-cost chemicals to mimic the mussel adhesion and has potential practical application in many fields.

Synthesis and self-assembly of tetraphenylethene and biphenyl based AIE-active triazoles

Self-assembly of fluorescent functional materials has attracted increasing interest in the fabrication of optoelectronic and biological nanodevices. Tetraphenylethene (TPE) is a typical dye molecule with aggregation-induced-emission (AIE) characteristics. Melding TPE carrying triple-bond functionality with diazide-containing biphenyl through “click” chemistry generates AIE-active luminogens [1,1′-biphenyl]-4,4′-diyl bis(6-(4-(4-(1,2,2-triphenylvinyl)phenyl)-1H-1,2,3-triazol-1-yl) hexanoate) [1(5)] and [1,1′-biphenyl]-4,4′-diyl bis(11-(4-(4-(1,2,2-triphenylvinyl)phenyl)-1H-1,2,3-triazol-1-yl) undecanoate) [1(10)] with solid state efficiencies up to unity. Slow addition of dilute THF solutions of 1(m) (m = 5, 10) into nonsolvents such as n-hexane and water yields self-assembled white wooly solids. TEM and SEM observations reveal the (helical) nanofibrous structure of the aggregates. Upon cooling from their concentrated hot solutions, 1(m) readily precipitate. Meanwhile, they can also form gels at high concentrations. Both precipitates and gels of 1(m) exhibit structures similar to those of the aggregates formed in nonsolvents. These results indicate that 1(m) can facilely self-assemble into high emission efficiency (helical) nanofibers, thus paving the way for their optoelectronic and biological applications.

Mesogen jacketed liquid crystalline polyacetylene containing triphenylene discogen: synthesis and phase structure

Triphenylene-containing acetylenes with one or three methylene units as spacers and the corresponding mesogen-jacketed liquid crystalline polyacetylenes (MJLCPAs) were designed and synthesized, the mesomorphic properties and phase behaviors of the monomers and novel side-chain liquid crystalline polymers were investigated. The monomers [HCC(CH2)mC18H6(OC6H13)5; m = 1, 3] are prepared by consecutive etherization, coupling, and etherization reactions, and the chemical structures were confirmed by mass spectroscopy and 1H/13C-NMR. The phase behaviors of the monomers were investigated by differential scanning calorimetry (DSC), polarized light microscopy (PLM), and wide-angle X-ray diffraction (WAXD). The results show that both of the monomers form a hexagonal columnar liquid crystal phase at room temperature. The monomers are polymerized using [Rh(nbd)Cl]2 as catalyst and producing soluble polymers in the yields of 55% and 52%, respectively. The chemical structures and phase behaviors of the two polymers are characterized and evaluated by IR, NMR, TGA, DSC, and WAXD analyses. Both of the two polymers show enhanced thermal and chemical stability with thermal decomposition temperatures up to higher than 340 °C due to the protection of the “jacketed effect” of the side-chain triphenylenes wrapped around the rigid polyacetylene main-chain. The polymers adopt a columnar shaped structure and self-organized into hexagonally packed columnar phase. The relative electron density maps of the columnar structure are also reconstructed.

Localized superplastic deformation of nanocrystalline 3Y-TZP ceramics under cyclic tensile fatigue at ambient temperature

Cyclic tensile fatigue tests were performed on 100±20 nm, and 0.35 μm 3Y-TZP ceramic specimens at room temperature. Localized superplastic deformation of the grains in the 100 nm material at and near to the fracture surfaces was first identified by AFM imaging. Slip band-like microfeatures, similar to those reported on some metals, were also unexpectedly seen to develop on the side faces. In contrast, the 0.35 μm specimens retained their equiaxed grain morphology after undergoing similar testing conditions. The micromechanisms underlining these phenomena were discussed. Grain boundary diffusion of the respective atomic species is reasoned to be the major governing process in operation. And the contribution of a dislocation slip mechanism is considered to play a possible or parallel role.

Relationship between performance and microvoids of aramid fibers revealed by two-dimensional small-angle X-ray scattering

Although the crystal structure in aramid fibers and the relationship between the size and orientation of crystallites and the performance of a material have been explored in detail, the effect of microvoids in an aramid fiber on its performance is still not clear. However, it is known that the mechanical properties depend strongly on the fiber morphology. In the present research, two-dimensional small-angle X-ray scattering is applied to characterize the microvoids in aramid fibers. Pauws two-dimensional full pattern fitting method and scattering model have been enhanced by introducing orientation parameters, such as zenith angle distribution and azimuthal angle distribution, and instrumental parameters like point spread function and beam profile function. A series of aramid fibers with different strengths were studied using the new two-dimensional full pattern fitting method to extract the microvoid parameters from the scattering patterns. The results show that the microvoids in the aramid fiber affect the fiber strength directly. The greater the number of spherical microvoids and the larger the ellipsoidal microvoids, the weaker the aramid fiber.

2D SAXS/WAXD analysis of pan carbon fiber microstructure in organic/inorganic transformation

Structure of PAN fibers during pre-oxidation and carbonization was studied using two dimensional small angle X-ray scattering/wide angle X-ray diffraction (2D SAXS/WAXD). The SAXS results show that during pre-oxidation between 180 °C and 275 °C, the volume content of microvoids increases with the temperature increasing, which may be one of reasons for the decrease of tensile strength of pre-oxidized fibers. 253 °C was the critical transition temperature, the length, diameter, aspect ratio and orientation distribution of microvoids increased with temperature before this temperature and decreased after this temperature. After the high temperature carbonization, lots of spindly microvoids formed. WAXD patterns demonstrate that the crystallite size of PAN fibers first increased before 230 °C and then decreased with the increase of temperature during the pre-oxidation. The diffraction peak of PAN fibers at 2θ ≈ 17° almost disappeared at the end of preoxidation while the diffraction peak of aromatic structure at 2θ ≈ 25° appeared at 253 °C. During carbonization, the peak intensity at 2θ ≈ 25° increased apparently due to the formation of graphite structure. The results obtained give a deep understanding of the microstructure development in the PAN fibers during pre-oxidation and carbonization, which is important for the preparation of high performance carbon fibers.

Effect of microgel content on the shear and extensional rheology of polyacrylonitrile solution

Crosslinked polyacrylonitrile (cPAN) particles with uniform size were synthesized through precipitation polymerization. The as-formed cPAN nanoparticles were dispersed in polyacrylonitrile (PAN) solutions to form microgels with various contents, which were used as model to study the influence of the microgels on the shear and extensional rheology of PAN solutions. Flow curves of steady shear viscosity displayed shear thinning and followed time–temperature superposition principle. The dependency of activation energy on the content of cPAN microgels indicated that introduction of microgels weakened the temperature sensitivity of PAN solutions. For extensional rheology study, we utilized the capillary thinning rheometry to characterize the elongation relaxation time and apparent extensional viscosity. Study of filament thinning dynamics with a series of system strains confirmed that the higher content of cPAN microgels the lower extensional strength and worse spinnability of the PAN solution.

Folding and birefringence behavior of poly(vinyl alcohol) hydrogel film induced by freezing and thawing

Band-like folds with high aspect ratio and birefringence behavior were observed on an in situ formed thin poly(vinyl alcohol) (PVA) hydrogel film via freezing–thawing treatment of PVA aqueous solution coated on glass. The crystallites generated during the freezing of the PVA solution cross-linked the PVA to form the hydrogel film. The volume expansion of the hydrogel film due to the absorption of condensed water in thawing induced the formation of folds. These folds show interesting birefringence behavior. The morphology, crystallization and birefringence behavior of the folds were characterized by polarized optical microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. A plausible principle for the fold formation is also discussed. It has been found that the moderate interaction between the hydrogel film and the substrate and the existence of condensed water on the frozen hydrogel film play important roles in the appearance of the folds.

Uniform core–shell nanobiscuits of Fe7S8@C for lithium-ion and sodium-ion batteries with excellent performance

Iron sulfides, as promising anode materials, have been intensively studied, but still encounter problems due to their limited cycle life caused by huge volume changes. In the present work, a facile method has been presented to prepare Fe2O3 nanobiscuits followed by poly(dopamine) coating. After thermally induced sulfurization, Fe7S8@C nanobiscuits have been successfully obtained, which show high specific capacities, excellent rate capabilities and stable cycling stability as anodes for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). They exhibit high reversible capacities of 547.3 mA h g−1 after 600 cycles and 530.8 mA h g−1 after 1000 cycles at a high current density of 5 A g−1 for LIBs and SIBs, respectively. This outstanding electrochemical performance may be attributed to the stress-buffering effect owing to the biscuit-like nanostructure and conformal surface coating with carbon.

Cu-enhanced photoelectronic and ethanol sensing properties of Cu2O/Cu nanocrystals prepared by one-step controllable synthesis

Metal nanocrystals are considered as effective components to enhance the photoelectronic properties of semiconductors. Herein, we report the enhancement of the photoelectronic response and photoelectronic catalysis on Cu2O by forming a Cu nanocrystal layer on its surface via a one-step approach. The photocurrent of Cu2O-rich Cu2O/Cu reaches 190 μA cm−2 in the first run and is about 4 times that of pure Cu2O. The cyclic voltammetry (CV) signal for methanol oxidation with Cu2O/Cu gives a higher methanol oxidation peak current than with that with Cu2O when irradiated by ultraviolet-visible light. The ethanol gas sensing performance of Cu2O-rich Cu2O/Cu hetero-nanocrystals is also investigated. It is shown that the sensitivity of the Cu2O-rich Cu2O/Cu hetero-nanocrystals is higher (4.83) than that of Cu2O nanocrystals (3.87) at an ethanol concentration of 2000 ppm.