聚乙烯管材的开裂动力学与机理

PE气体管材在室温低应力长期作用下发生开裂破坏的过程是由较长时间的裂纹慢速增长(SCG)阶段和较短时间的快速增长阶段(FCG)构成的.通过预测SCG阶段的持续时间可以预测PE材料的使用寿命,而SCG阶段可由PE的拉伸试验和三点弯曲试验进行模拟并用Dugdale理论处理.用弯曲试验来模拟预测PE开裂破坏时间的式子为■PE的这种开裂破坏是由连结分子的解缠滑脱作用造成的.在宏观上表现为脆性断裂.它受应力、温度、试样切口深度以及分子量与分子量分布、支化情况和结晶情况等因素的影响.改变这些因素能够使断裂机理发生改变,从而改变PE材料的使用寿命.     

Measuring Charge Distribution of Molecular Cations by an Atomic Coulomb Probe Microscope

Imaging the charge distributions and structures of molecules and clusters will promote the understanding of the dynamics of the quantum system.Here,we report a method by using an Ar atom as a tip to probe the charge distributions of benzene(Bz) cations in gas phase.Remarkably,the measured charge distributions of Bz⁺(δ_H=0.204,δ_C=-0.037) and Bz²⁺(δ_H=0.248,δ_C=0.0853) agree well with the calculated Mulliken distributions,and the struc...     

超快飞秒激光场中原子分子量子态调控

超快激光及其调控技术的发展使得原子分子量子态超快测控受到广泛关注,这些研究加深了对强激光与原子分子量子态相互作用的认识。本文回顾了相关领域的研究进展,特别集中在超快激光场对分子转动、解离的调控以及原子分子电离的量子态调控的研究,并对未来发展进行了展望。     

Ultrafast Coulomb explosion imaging of molecules and molecular clusters

Taking an image of their structure and a movie of their dynamics of small quantum systems have always been a dream of physicists and chemists. Laser-induced Coulomb explosion imaging (CEI) provides a great opportunity to make this dream a reality for small molecules or their aggregation —— clusters. The method is unique for identifying the atomic locations with ångstrom spatial resolution and capturing the structural evolution with a femtosecond time scale, in particular for imaging transient state products. This review summarizes the determination of three-dimensional equilibrium geometry of molecules and molecular cluster system through the reconstruction from the fragments momenta, and also shows that the dissociation dynamics on the complex potential energy surface can be tracked in real-time with the ultrafast CEI (UCEI). Furthermore, the detailed measurement and analysis procedures of the CEI, theoretical methods, exemplary results, and future perspectives of the technique are described.     

Ca0.5Sr0.5TiO3弹性和热学性质的第一性原理研究

利用能量最小原理, 确定了Ca_0.5Sr_0.5TiO₃晶体中4c位置的Ca/Sr原子对称分布, 建立了Ca_0.5Sr_0.5TiO₃稳定的晶体结构, 在此基础上利用基于密度泛函理论第一性原理的平面波超软赝势方法, 采用局域密度近似和广义梯度近似函数, 计算了Ca_0.5Sr_0.5TiO₃的晶格参数、弹性常数、体弹模量、剪切模量、杨氏模量、泊松比, 并基于Christoffel方程的本征值研究了平面声波的特征, 基于Cahill和Cahill-Pohl模型研究了最小热导率的特征. 计算结果表明: Ca_0.5Sr_0.5TiO₃晶格参数和实验值很接近, 体弹模量大于剪切模量, [100], [010], [001]晶向的杨氏模量、泊松比、普适弹性常数(A^U)以及杨氏模量三维图均显示了弹性各向异性; 平面声波在(010), (001)平面呈现各向异性, 在(100)平面呈现各向同性, 平面声波大小与平均横波和平均纵波的数值很接近. Cahill模型最小热导率在各平面呈现各向同性, Cahill-Pohl模型最小热导率在高温时趋于恒定. 准谐德拜模型下Ca_0.5Sr_0.5TiO₃ 晶体的摩尔热容和热膨胀系数与CaTiO₃晶体的接近, 并且高温下具有稳定的热膨胀性能. 计算所得禁带宽度为2.19 eV, 导带底主要是Ti-3d与O-2p态电子贡献; 由电荷布居和电荷密度图理论证实Ca_0.5Sr_0.5TiO₃具有稳定的Ti-O八面体结构.     

可生物降解聚合物乙肝疫苗微球的制备和表征

采用双乳液体系（Ｗ１／Ｏ／Ｗ２）溶剂抽提法制备了聚－ＤＬ－乳酸－聚乙二醇嵌段共聚物（Ｐｏｌｙ－ｄｌｌａｃｔｉｄｅ－ｂ－ｐｏｌｙｅｔｈｙｌｅｎｅ ｇｌｙｃｏｌ,ＰＥＬＡ）包裹乙肝表面抗原（ＨＢｓＡｇ）微球。微球外观规整,平均粒径２．１７μｍ,抗原包裹量达１．２５％,包裹效率７１．８％。经聚丙烯酰胺凝胶电泳（ＰＡＧＥ）检测,ＨＢｓＡｇ在微球制备过程中保持了结构完整性。以乙肝常规铝佐剂疫苗为对照,ＢＡＬ     

ENHANCEMENT OF COMPATIBILITY OF POLYPROPYLENE AND NYLON-66 BY MALEATED POLYPROPYLENE

The compatibility of PP/N-66 blending system modified with maleated polypropylene was studied by means of SEM, DMA and other mechanical testing. It was found that when proper amount of modifier was applied, the compatibility was greatly enhanced and the impact toughness was significantly improved. An important direct evidence of the formation of the interfacial copolymer was also found. However, when excessive amount of modifier was used, the modification effect was not conspicuous. The phenomena were interpreted from a view of molecular motion that the interfacial block copolymer forced the two components to 'compatibilize' and many flexible PP molecules were set free from the restraint of the crystallites of plain PP so as to absorb much more impact energy.