Review of some recent progress on materials science researches in China

New materials have become one of the most important and fastest-growing industries all over the world.Important progress in materials science and technology has produced profound influences on the national economy,daily life and national defense of our country.In this paper,we review the state of the art of materials science and technology in China,with emphasis on recent research focuses and advanced technology.     

Characterization of structural knot distributions in UHMWPE fibers

Microbeam wide-angle X-ray diffraction (WAXD) experiments were carried out at different structural knot positions of SIOC and M4 fibers of ultra-high molecular weight polyethylene (UHMWPE). The optical microscope images revealed that SIOC fiber had bamboo-like structural knots, and M4 fiber had chaotic distribution of structural knots. WAXD patterns showed the monoclinic unit cell in the whole M4 fiber, but different lamellar orientations in the bamboo joint of SIOC fiber. In addition, small-angle X-ray scattering (SAXS) patterns confirmed that the SIOC fiber contained uniform distribution of shish structures, and differential scanning calorimetry (DSC) measurements showed that its less branched and short chains benefited the orthorhombic-hexagonal phase transformation.     

Imidazole-buffered acidic catholytes for hybrid Li–air batteries with high practical energy density

Hybrid Li–air batteries with acidic catholyte offer high cell voltage and are stable with CO₂ in air. However, the practical capacity of the acidic catholyte is limited by the low concentration of acids utilized and the limited solubility of the discharge products. Only weak acids or diluted strong acids with limited practical capacity are generally used due to the poor stability of the solid electrolyte in low pH solution. We show here the pH of high-concentration, strong acids can be increased to near neutral values by forming a buffer with imidazole additive, which can be used in hybrid Li–air batteries. With the addition of 6.06 mol L^− 1 of imidazole to 6 mol L^− 1 HCl, the solution has a mild pH of ~ 5.0, facilitating the operation of hybrid Li–air batteries with high practical capacity and stability.     

Selective solvent annealing induced phase separation and dewetting in PMMA/SAN blend ultrathin films

Phase behaviors induced by solvent annealing in poly(methyl methacrylate) (PMMA) and poly(styrene‐ran‐acrylonitrile) (SAN) blend ultrathin films have been investigated by atomic force microscopy and grazing incidence small‐angle X‐ray scattering. Our results indicate that both the phase separation within the blend and the dewetting of the film induced by composition fluctuation take place upon the selective solvent annealing, producing complex structures containing upper droplets (of one phase) and mimic‐films (of the other rich‐phase). The use of acetic acid (the selective solvent for PMMA) generates PMMA mimic‐film and SAN droplets, while the introduction of DMF (exhibiting better solubility for SAN) vapor results in the formation of SAN mimic‐film and PMMA droplets. Essentially, the interaction at polymer/substrate interface, resultant wettability of selected component, solubility of PMMA and SAN in adopted solvent dominate not only the phase separation and the dewetting of the whole film but also the synergism of them. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1243–1251     

PolyHIPEs块体的磺化改性及其吸附研究

以乙酰磺酸酯为磺化剂,对不同内相比的高内相比乳液聚合所得多孔聚合物块体(polyHIPEs)进行磺化改性处理,通过傅立叶变换红外光谱(FT-IR)、电导滴定、紫外-可见-近红外分光光度计等对磺化产物及其吸附性能进行了表征。结果表明,polyHIPEs已被成功磺化,磺化后块体表面的亲水亲油性发生了明显的变化,其吸水性明显增强,而吸油性明显减弱。由于引入了带负电荷的磺酸基团(-SO3H),其对正离子或带正电荷的分子(如亚甲基蓝染料)具有较强的吸附性能。同时,磺化后的块体具有一定的pH敏感性。     

Surface and interface properties of carbon fiber composites under cyclical aging

Carbon fiber-reinforced BMI composites have been subjected to combination accelerated aging comprising a hygrothermal process, a thermal-oxidative process, and a freezing process in order to simulate their responses under complicated service environments. This cyclical condition, including the freezing process, has not been investigated by other researchers so far. The effects of this combination accelerated aging on the mechanical properties have been characterized by FTIR, SEM/EDXA, XRD, and moisture-uptake determination. The results indicated that combination accelerated aging had great effects on the mechanical properties of the composite, the network structure of the BMI matrix, and the moisture uptake by the composite. After a third cycle of accelerated aging, moisture reached the center layer of the composite and as a result led to an obvious decrease in ILSS due to deterioration of the carbon fiber-BMI interface. Sufficient moisture absorption on the composite surface made the network structure of the BMI matrix more open, which facilitated stress relaxation and the creation of micro-cracks, with a consequent obvious decrease in flexural strength. With increasing number of combined-action accelerated aging cycles, ever more moisture was absorbed during each hygrothermal process due to the plasticizing effect of water, and micro-cracks propagated as a result of internal stresses caused by the hygrothermal process, the thermal-oxidative process, and the freezing process of each cycle. XRD analysis indicated that moisture penetrated through the amorphous region of the BMI matrix.     

Facile fabrication of cerium niobate nano-crystalline fibers by electrospinning technology

In this study, one-dimensional (1D) cerium niobate nano-crystalline fibers were first prepared by a facile sol–gel and electrospinning process, followed by heat treatment. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM) were used to characterize the samples. It can be seen from SEM images that the as-prepared xerogel samples and those annealed at 900 °C presented uniform fibrous morphology, with the diameter of 100–300 nm and length of several centimeters. The XRD and FT-IR results showed that cerium niobate samples had well-crystallized phase of CeNbO_4.25 with the crystallite size of about 28.6 nm at a heat treatment temperature of 900 °C, which can also be validated with the TEM image. The AC impedance of annealed disks made from the CeNbO_4.25 nano-crystalline fibers has been probed.     

Enhanced cycle ability of spinel LiMn2O4 by controlling the phase purity and structural strain

By applying the annealing step during the solid-state synthesis, well-crystallized spinel LiMn₂O₄ with high phase purity was fabricated. The sensitive effect of heating procedure on the structural and electrochemical properties of LiMn₂O₄ product was investigated. It was found that preheat-treatment-calcinations-annealing process can effectively eliminate the impurity phase. The post-annealing process also leads to a better crystalline and suitable strain for the LiMn₂O₄ product, which contributes to the enhanced cycling performance.