Strain-induced crystallization in elongated polyisobutylene elastomers

Elastomeric networks were prepared from a sample of polyisobutylene having 2 mol% isoprene units as unsaturated sites for free-radical crosslinking. Four samples having different degrees of crosslinking were obtained by peroxide thermolysis, and were then studied with regard to their thermoelastic properties in elongation. Each network strip was elongated at 338 K to ensure that it was completely amorphous, and then held at this constant length. The temperature was then slowly decreased at intervals, and the equilibrium value of the elastic force recorded for each temperature. The temperatures at which crystallization was observed from changes in the stress-temperature dependence were taken to be approximate melting points. The temperature range over which crystallization occurred was found to narrow considerably with increase in elongation. It was found that at lower elongations, the nominal melting points increased gradually with increase in elongation, while at higher elongations, their dependence on elongation became linear and more pronounced. The dependence of the melting points on the molecular weights between crosslinks and on strain were documented, and then compared with relevant theory. For each degree of crosslinking, estimated degrees of crystallinity were found to increase substantially and linearly with increase in elongation.     

The configuration space of low-dimensional Yang-Mills theories

We discuss the construction of the physical configuration space for Yang-Mills quantum mechanics and Yang-Mills theory on a cylinder. We explicitly eliminate the redundant degrees of freedom by either fixing a gauge or introducing gauge invariant variables. Both methods are shown to be equivalent if the Gribov problem is treated properly and the necessary boundary identifications on the Gribov horizon are performed. In addition, we analyze the significance of non-generic configurations and clarify the relation between the Gribov problem and coordinate singularities.     

CH3Cl adsorption on a Si(100)2 × 1 surface modified by alkali metal overlayer studied by soft X-ray photoemission using synchrotron radiation

We present the first study of the effect of an alkali metal overlayer on the adsorption of an organic molecule, methylchloride, on a Si(100)2 × 1 surface. In strong contrast to the behavior of molecular oxygen or nitrogen which were found to react with the silicon substrate, there was no significant interaction between methylchloride and silicon, rather, the formation of alkali-chlorine bonds was observed. Core level and valence band spectroscopies using synchrotron radiation were used to study these systems. Sodium was found to exhibit the strongest interaction with mehtylchloride which was dissociated, while the effects produced by K and Cs were weaker.     

Structure and magnetic properties of a novel copper diphosphonate with pillared layered structure:: Cu2(H2O)2{O3PCH2N(C2H4)2NCH2PO3}

Compound Cu₂(H₂O)₂{O₃PCH₂N(C₂H₄)₂NCH₂PO₃} (1) has a pillared layered structure in which the organic groups of N,N′-piperazinebis(methylenephosphonate) are sandwiched between the inorganic layers. Compared with other copper phosphonates with layered or pillared layered structures, the inorganic layer in 1 is unique in that each {CPO₃} tetrahedron is corner-shared with three {CuO₄N} square pyramids through three oxygen donors. Ferromagnetic interactions are mediated between the metal centers. Crystal data: Pbca, a=10.0830(16) Å, b=9.4517(15) Å, c=13.218(2) Å, V=1259.7(3) Å³, Z=4.     

Preparation and characterization of polymer-capped CdS nanocrystals

Poly(vinyl pyrrolidone) (PVP)-capped CdS nanoparticles were prepared with CS₂ as the sulfur source through the hydrothermal process. The obtained nanoparticles were characterized by X-ray diffraction, transmission electron microscopic, ultraviolet–visible and fluorescence spectroscopy. The capped CdS nanoparticles showed remarkable stability and significantly enhanced luminescence property compared with that of the noncapped ones. We attributed this observation to the surface passivation of the CdS nanoparticles by the PVP molecules.     

Creation of a stereoselective solid surface by self-assembly of a chiral metal complex onto a nano-thick clay film

A stereoselective solid surface has been created by the self-assembly of a chiral osmium complex, λ-[Os(phen)₃](ClO₄)₂ (phen=1,10-phenanthroline), onto a single layered clay film deposited on an indium tin oxide (ITO) electrode; the Os^II–Os^III redox couple mediates the electrochemical oxidation of chiral 1,1^′-2-binaphthol in a stereoselective way or the S-isomer is oxidized at 1.4 times higher rate than the R-isomer.     

多羟基化合物键合亲水色谱固定相的制备及其分离性能

用硅胶与氨丙基三甲氧基硅烷反应,再与δ-葡萄糖酸内酯反应,制备了一种多羟基化合物键合的新型亲水色谱固定相。以水-有机溶剂(乙醇、乙腈、四氢呋喃)为流动相,通过改变流动相中有机溶剂的种类及浓度、缓冲盐浓度和柱温,考察了该固定相对6种强极性中药组分的保留行为和保留机理。当水的比例在0～40%(v/v)范围时,溶质的保留随着流动相中水的比例的增大而减小,属于典型的亲水色谱分离模式;而当流动相中水的比例在0～100%(v/v)范围内变化时,溶质的保留随着水的比例变化呈“U”形曲线,属于亲水色谱和反相色谱的混合保留机理。缓冲盐的浓度和pH效应说明,所选用的中药组分与所制备的固定相间还存在弱的静电作用。该固定相对6种中药组分以及丹参注射液具有良好的分离性能,表明其在强极性中药有效成分的分离及其他强极性物质的分离分析中具有一定的应用前景。