Pattern forming precipitation in gels due to coupling of chemical reactions with diffusion

Precipitate-forming chemical reactions have been studied in chemically cross-linked poly(vinyl alcohol) gel medium. One of the reactive components was incorporated into the gel, the other was allowed to diffuse into it. Depending on the experimental conditions the reaction-diffusion process often results in patterns of different type. Experiments performed in tubes and in thin layers were carried out in order to investigate the effects of various factors (cross-linking density, swelling degree as well as the concentrations of the outer and inner electrolytes) on the morphologies of the precipitate patterns. It was found that precipitation occurs not only in the Liesegang bands, but also between bands. Beside Liesegang-type structures, tree-like patterns have been observed, showing a characteristic periodicity in the density profile obtained by digitalized image analyses.     

Calorimetric study of Diepoxide Chain-Extended Poly(Ethylene Terephthalate)

A series of chain-extended PET samples were obtained by the use of different amounts of a diepoxide as chain extender, which was prepared for this purpose. These samples exhibited different intrinsic viscosities and degrees of branching or cross-linking. The effects of this differentiation on the thermal properties were studied by differential scanning calorimetry. The thermal parameters studied were the glass transition temperature (T_g), the cold-crystallization temperature (T_cc), the melting temperature (T_m), the enthalpy (ΔH_m) and the degree of crystallinity. The data revealed that, the higher the quantity of chain extender or the chain extension time, the higher T_gand T_cc, but the lower T_mand ΔH_m, i.e. the more amorphous the chain-extended samples, as also shown by density measurements. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal behaviour of styrene butadiene rubber/poly(ethylene-co-vinyl acetate) blends

The thermal behaviour of styrene butadiene rubber (SBR)/poly (ethylene-co-vinyl acetate) (EVA) blends was studied by using thermogravimetry (TG) and differential scanning calorimetry (DSC). The effects of blend ratio, cross-linking systems and compatibilization on the thermal stability and phase transition of the blends were analyzed. It was found that the mass loss of the blends at any temperature was lower than that of the components, highlighting the advantage of blending SBR and EVA. The addition of compatibilizer was also found to improve the thermal stability. DSC studies indicated the thermodynamic immiscibility of SBR/EVA system even in the presence of the compatibilizer. This is evident from the presence of two different glass transition temperatures, corresponding to SBR and EVA phases in both compatibilized and uncompatibilized blends.     

接枝和交联对纳米Si02改性NR／PP共混型热塑弹性体的影响

动态硫化制备纳米二氧化硅（SiO2）改性天然橡胶，聚丙烯共混型热塑性弹性体（NR/PPTPE）．研究了马来酸酐，苯乙烯，过氧化二异丙苯（MAH／St／DCP）多单体“就地”熔融接枝、交联对TPE力学性能、耐溶剂性能和耐热变形性能的影响，并用SEM分析了TPE的断面形貌．结果表明：纳米SiO2和MAH／St／DCP的最佳质量分数分别为0．03和0．0375／0．0188／0．00375时，MAH／St／DCP接枝、交联改性NR／PP／纳米SiO：TPE的力学性能、耐溶剂性能和耐热变形性能最佳．MAH／St／DCP“就地”接枝、交联通过细化交联NR分散相、改善交联NR分散的均匀性和增加两相之间的共交联，使NR与PP两相界面结合强度明显提高，NR／PPTPE的综合性能得到明显的改善．     

辐照对聚己内酯结构和性能的影响

研究了γ 辐照对不同分子量的聚己内酯 (PCL)的力学性能、热性能、结晶行为的影响 ,在此基础上 ,研究了辐射交联后的PCL的形状记忆行为 .研究结果表明 ,PCL的分子量越大 ,辐射交联所需的凝胶化剂量越低 .溶胶分数S +S1 2 与 1 D的关系很好地符合Charlesby Pinner关系式 ,说明PCL的辐射交联属于无规交联 .剂量对PCL的力学性能影响显著 ,剂量越大 ,抗张强度和断裂伸长率下降越多 ,但分子量较高的PCL的抗张强度受剂量的影响较小 .DMA分析表明 ,聚己内酯辐照交联后的弹性模量和耐热性能显著提高 .交联度较高的PCL表现出高弹态 ,可以拉伸 ,并具有较好的形状记忆行为 .DSC分析表明 ,辐射交联使PCL的结晶度有所增加 ,但也使结晶熔点有所降低     

CROSS-LINKING OF AROMATIC POLY（THIOETHER）S

A novel cross-linking process using two high molecular weight aromatic poly(thioether)s,which were synthesized by the reactions of 4,4′-thiobisbenzenethiol with 4,4′-difluorobenzophenone and 4,4′-difluorodiphenylsulfone,respectively, and commercially available lower molecular weight poly(p-phenylene sulfide)was investigated.These reactions were carried out in bulk by the addition of silver tetrafluroborate andα,α′-dibromo-p-xylene at 190℃over a period of 45 min. Furthermore,the same procedure could be modified to cross-link compression-molded films of these three polymers.The thermal and solubility behaviors of these polymers before and after cross-linking reactions,are presented.     

用热聚法固定指示剂的光纤氧气传感器研究

采用热聚法将甲叉双丙烯酰胺（MBBA）聚合并共价交联在硅烷化的玻璃微珠上 ，同时将指示剂Ru（Ⅱ）-邻啡咯啉配合物物理包埋于聚合物中，研制了一种基于 荧光猝灭原理的光纤氧气传感器，采用NaHSO_3-O_2-MnSO_4体系引发MBBA水溶液热 聚合后应，通过确定NaHSO_3,MnSO_4,MBBA和Ru(phen)_3Cl_2的最佳反应浓度以及 玻璃微珠的尺寸，优化了聚合反应条件，改善了指示剂的固定效果，制备了性能较 好的传感器探头，该传感器的检测下限为5×10~(-6)(V/V)，响应时间为10s该传感 器连续工作50min,重复性标准偏差为±1%。     

Photovoltaic and spectral properties of tetraphenyloporphyrin and metallotetraphenyloporphyrin dyes

Spectroscopical properties and photocurrent (or photovoltage) of tetraphenyloporphyrins and metallotetraphenyloporphyrins in nematic liquid crystal have been studied. Photoelectric response has been measured in an electrochemical cell made of the semitransparent semiconducting and golden electrodes with porphyrin dyes embedded in liquid crystal. Fluorescence, time-resolved luminescence in microsecond time scale and photoacoustic spectra have also been measured. The competition between radiative, non-radiative processes and charge transfer is discussed. It has been shown that effectivity of porphyrins for photocurrent generation depends on the presence/absence of central metal in the macrocycle of porphyrin skeleton and the kind of metal. The schematic model of the contributions of the dye molecule and semiconducting electrode in the electron transfer process is shown.     

A bi-virus competing model with time-varying susceptibility and repeated infection

This paper introduces a bi-virus model with time-varying susceptibility. The model describes the case that there coexist two viruses and the time-varying susceptibility due to repeated infections. For different parameters, we investigate the stability of various equilibriums. Under appropriate conditions the two viruses show competitive relationship, that is, one virus will eventually become a pandemic, and the other virus will eventually disappear. For this case, we further study the dynamical behavior of virus transmission. The model shows some new phenomena, that is, the outbreak of the virus will be delayed appropriately, giving people an illusion. Finally, we present a numerical example to illustrate the effectiveness of the theoretical results.     

Fe2O3-ZrO2层柱蒙脱石的合成和热稳定性

蒙脱石是具有2∶1层状结构的粘土矿物,酸化蒙脱石用途广泛[1]。利用较大体积多聚金属阳离子与蒙脱石进行离子交换并把蒙脱石层撑开,可以得到复合材料—层柱蒙脱石(ＰＩＬＭ),它具有二维的层柱结构,其孔径比一般的分子筛大。其孔径还可以根据蒙脱石离子交换当量和交换阳离子的体积大小加以控制。它具有良好的热稳定性和酸性,并且合成方法简单。蒙脱石和膨润土在我国分布广泛,储量大。因此ＰＩＬＭ在载体、吸附剂及较大分子转化催化剂等方面具有较好的应用前景。传统的层柱蒙脱石是由单组分多聚金属阳离子与蒙脱石进行交联而合成的,本文在…