熔融插层法制备LLDPE/MgAl-LDH 剥离型纳米复合材料及其热性能研究

The interlayer surface of MgAl layered double hydroxide （MgAl-LDH） was modified by exchanging about half of the interlayer nitrate anions by dodecyl sulfate anions （DS） to get MgAl（H-DS） LDH, and then the MgAl（H-DS） was melt intercalated by LLDPE to get the LLDPE/MgAl-LDH exfoliation nanocomposites. The samples were characterized by Fourier transform infrared （PTIR） spectroscopy, X-ray diffraction （XRD）, ion chromatography, transmission electron microscopy （TEM）, and thermogravimetry analysis （TGA）. The nanoscale dispersion of MgAl-LDH layers in the LLDPE matrix was verified by the disappearance of （001） XRD reflection of the modified MgAl-LDH and by the TEM observation. The TGA profiles of LLDPE/MgAl-LDH nanocomposites show a faster charring process between 210 and 370 ℃ and a higher thermal stability above 370 ℃than LLDPE. The decomposition temperature of the nanocomposites with 10 wt% MgAl（H-DS） can be 42 ℃ higher than that of LLDPE at 40% weight loss.     

基于正电子的反物质研究进展

正电子是最容易获得的反粒子,因而电子-正电子系统最适合研究普通物质与反物质的结合.本文结合最近实验上首次合成物质-反物质分子这个重大发现,介绍反物质(正电子)研究历史、现状及展望;重点讨论基于正电子的捕获、约束、积累等实验技术,以及物质-反物质分子--正电子素分子的合成方法.     

Neutron Star Composition in Strong Magnetic Fields

We study the neutron star composition in the presence of a strong magnetic field. The effects of the anomalousmagnetic moments of both nucleons and electrons are investigated in relativistic mean field calculations for afl-equilibrium system. Since neutrons are fully spin polarized in a large field, generally speaking, the protonfraction can never exceed the field free case. An extremely strong magnetic field may lead to a pure neutronmatter instead of a proton-rich matter.     

Resistivity-Temperature Behavior of CB-Filled HDPE Foaming Composites

High-density polyethylene/carbon black foaming conductive composites were prepared from acetylene black（ACEY） and super conductive carbon black（HG-1P） as conductive filler, low-density polyethylene（LDPE） as the second component, ethylene-vinyl acetate（EVA） and ethylene propylene rubber（EPR） as the third component, azobisformamide（AC） as foamer, and dicumyl peroxide（DCP） as cross-linker. The structure and resistivity-temperature behavior of high-density polyethylene（HDPE）/CB foaming conductive composites were investigated. Influences of carbon black, LDPE, EVA, EPR, AC, and DCP on the foaming performance and resistivity-temperature behavior of HDPE/CB foaming conductive composites were also studied. The results reveal that HDPE/CB foaming conductive composite exhibits better switching characteristic; ACET-filled HDPE foaming conductive composite displays better positive temperature coefficient（PYC） effect; whereas super conductive carbon black（HG-1P）-filled HDPE foaming conductive composite shows better negative temperature coefficient（NTC） effect.     

EFFECT OF PROCESSING METHOD ON THE IMPACT STRENGTH OF POM/TPU/CaCO3 TERNARY COMPOSITES

Polyoxymethylene （POM）/elastomer/filler ternary composites were prepared, in which thermoplastic polyurethane （TPU） and inorganic filler, namely, CaCO3, were used to achieve balanced mechanical properties of POM. The dispersion and phase morphology of POM/elastomer/filler composites were found to depend largely on processing method, CaCO3 content in masterbatch and the filler size. Two processing methods were employed to prepare POM/elastomer/filler ternary composites. One is called the one-step method, in which elastomer and the filler directly melt blended with POM matrix. The other is called the two-step method, in which the elastomer and the filler were mixed to get masterbatch first, which was then melt blended with pure POM of different content. The effect of phase morphology and processing method on impact strength was investigated. It was found that the two-step method results in an increase in impact strength but not for the one-step method. Additionally, the impact strength of POM ternary composites decreases with the increase in the size of CaCO3 particles.     

A New Method to Synthesize Polytitanosilazane as Ceramic Precursor

A new kind of polytitanosilazane precursor PTSZ for Si/C/N/Ti-based ceramic was synthesized from the condensation reaction of silazane lithium salt and titanium tetrachloride (TiCl4). The results indicated that the ceramic yield of PTSZ was much higher than that of corresponding silazane oligomer.     

STUDY ON THE DESALINATION BEHAVIORS OF PA/PSF THIN FILM COMPOSITE

A polypiperazine amide (PA)/polysulfone (PSF) thin film composite (TFC) was prepared by interfacial polymerization (IP) using a trimesoyl chloride hexane solution as the oil phase and a piperazine aqueous solution as the water phase on a porous polysulfone hollow fiber substrate. Its separating behaviors were investigated systematically to various salts such as NaCl, KCI, Na2SO4,MgCl2, CaCl2 and MgSO4, showing the highest rejection rate to Na2SO4, the second to MgSO4, the third to MgCl2 and CaCl2, and the lowest to KCI, NaCl, being 99%, 98%, 70%, 60%, 15% and 10% respectively. Under an increasing pressure or with time, the rejection rate of the TFC rises to a plateau. To various concentration of the feed, the rejection rate reduced gradually with the higher concentration.     

Preparation, Characterization and Magnetic Properties of PANI/La-substituted LiNi Ferrite Nanocomposites

Magnetic nanocomposites containing polyaniline （PANI）-coated La-substituted LiNi ferrite （LiNi0.5La0.02Fe1.98O4） were synthesized by in situ polymerization in aqueous solution of hydrochloric acid. The nanocomposites exhibited the magnetic hysteresis nature under applied magnetic field. The saturation magnetization （Ms） and coercivity （Hc） varied with the ferrite content. The obtained nanocomposites were characterized by X-ray diffraction （XRD）, transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, Fourier transform infrared spectroscopy （FT-IR）, UV-Visible spectroscopy and vibrating sample magnetometer （VSM）. TEM and SEM studies showed that the nanocomposites present the core-shell structure. The results of XRD patterns, FT-IR and UV-Visible spectra indicated the formation of PANI-LiNi0.5La0.002Fe1.98O4 nanocomposites and showed that the interaction existed between PANI backbone and ferrite particles in the nanocomposites. The bonding mechanism in the nanocomposites has been proposed.     

Studies on Kinetics of Crystallization of PA6／UFAPR Composites

The influence of Ultrafine Full-Vulcanized Acrylate Powdered Rubber(UFAPR) on the isothermal crys-tallization kinetics and nonisothermal crystallization behavior of PA8 has been studied by means of DSC. The results show that with the introduction of a small amount of UFAPR, the crystallization rate of PA8 can be increased obviously, and the crystallization temperature range can be augmented and the crystallite size distri-bution of the crystal can be narrowed down. The change of free energy perpendicular to the crystal nucleus, which has been calculated according to the Hoffman theory, is consistent with the result of Avrami′s equa-tion. The unit surface free energy of the radial-developing crystal spherulite decreases while the crystalliza-tion rate of PA8 increases with the introduction of UFAPR. Meanwhile, it is shown by means of the polariz-ing microscope(PLM) that the crystal size drops down and the number of the crystal grains augments with the addition of UFAPR, which shows that UFAPR can function as a nucleating agent.     

Dielectric responses of graded composites having generalized gradation profiles

Under an external uniform electric field, the dielectric response of graded cylindrical composites having generalized dielectric profile inclusions is investigated. The generalized dielectric profile of graded cylindrical inclusion is expressed in the form, $\varepsilon _i (r)=c(b+ r)^k\e^{\beta r}$ where $r$ is the radial variable of the cylindrical inclusions and $c$, $b$, $k$ and $\beta $ are parameters. The local potential solution of generalized dielectric profile graded composites is derived by means of the power series method and the effective dielectric response is predicted in the dilute limit. Moreover, from the result of generalized profile, the analytical solutions of local potentials and the effective responses of graded composites having three cases of dielectric profiles, i.e., the exponential profile $\varepsilon_\i (r)=c\e^{\beta r}$, the general power law profile $\varepsilon_\i (r)=c(b+r)^k$ and the profile $\varepsilon_\i (r)=cr^k\e^{\beta r}$, are sorted out, respectively. In the dilute limit, our exact results are used to test the validity of differential effective dipole approximation (DEDA) for estimating the effective response of graded cylindrical composites, and it is shown that the DEDA is in excellent agreement with the exact result.