Surface segregation of silicon impurities in organic materials

The present revolution in novel organic materials is driven by the synthesis of new materials exhibiting specific functional properties. Traces of silicon compounds are often present in these materials and, although the bulk concentrations of these impurities may be low, segregation can seriously modify the surface composition. Surfaces and interfaces play an important role in many applications, and the intrinsic properties of the materials are thus often obscured by the presence of segregated impurities. By studying silicon impurity segregation in poly‐dialkoxy phenylenevinylene (PPV), polycarbonate and dendrimer macromolecules, we demonstrate how low‐energy ion scattering may be used to determine the surface impurity fraction and to observe which groups at the surface are shielded by the segregated species. We demonstrate that the performance of PPV‐ based light‐emitting diodes is significantly reduced for submonolayer coverages of siloxanes. We find that the kinetics of the segregation process depend strongly on the materials and the sample preparation conditions. We find that the presence of solvents is needed to enable segregation at room temperature. Heating does enable siloxane impurity segregation in polycarbonate in the solid phase, whereas for polydimethylsiloxane in PPV films we find that segregation in the solid phase does not occur up to 200 °C. The siloxane molecules are found to segregate to preferential sites at the surface, shielding the polar groups. Finally, we demonstrate that purification of the surface is often possible through simple procedures that provide an easy way to study the intrinsic properties of the materials. Copyright © 2004 John Wiley & Sons, Ltd.     

SEM,SAED, and TEM investigations of domain structure in PZT ceramics at morphotropic phase boundary

SEM investigations of ferroelectric domain structure in PbZr_0.53Ti_0.47O₃ are consistent with a model of spatial domain configuration for the piezoelectric ceramics previously proposed for BaTiO₃. TEM and SAED results revealed not only the twinning relation of adjacent tetragonal 90° domains but also the simultaneous presence of the ferroelectric rhombohedral phase. A succession model of ferroelectric domains T₁RT₂RT₁... which needs a smaller energy for the rotation of the polarization vector due to the coexistence of a R domain between the two T 90° domains is proposed. This model is also confirmed by the estimated value of elastically stored energy in the mixed wall and by the dependence upon the sintering temperature of T and R unit cell distortions previously measured by x-ray diffraction.     

64Cu放射性药物化学

64Cu半衰期为12.7 h,其衰变过程既发射β+粒子(β+,0.655 MeV,17.8%),又发射β-粒子(β-,0.573 MeV,38.4%)。近20年来,随着铜配位化学的发展,新型配体不断出现(如DOTA、TETA、NOTA、CB-TE2A、C3B-DO2A等)。Cu(Ⅱ)的络合物在生物体内/外的稳定性不断提高,64Cu已经成功标记在氨基酸、多肽、蛋白、核酸等分子以及纳米颗粒上。64Cu可制成正电子显像药物用作诊断,同时也有发展为放射性治疗药物的潜力。新型铜配体和标记方法以及新的药物靶标的研究已经成为64Cu放射性药物研究的热点,至今已研制出了多种64Cu标记的放射性药物,如64Cu-ATSM是有效的肿瘤乏氧显像剂,64Cu-PTSM是优良的血流示踪剂等。本文旨在介绍64Cu(Ⅱ)几种主要类型的含氮配体以及64Cu标记的放射性药物在显像和治疗方面的最新研究进展,并展望其发展趋势。     

Interaction between star-like block copolymer and sodium oleate in aqueous solutions

The interaction between a star-like block copolymer (AP432) and an anionic surfactant sodium oleate (C₁₇H₃₃COONa) was investigated in detail both at the air/water interface and in bulk aqueous solutions. The results of surface tension show that AP432 and C₁₇H₃₃COONa could form mixed micelles. The results obtained from the oscillating barrier measurements at low dilational frequencies (0.01-0.1 Hz) reveal that the maximum values of the dilational modulus for AP432/C₁₇H₃₃COONa mixed system moved to lower concentrations compared to those of single AP432 or C₁₇H₃₃COONa aqueous solutions. Steady-state fluorescence measurements indicate that after mixing, the I₁/I₃ values of AP432/C₁₇H₃₃COONa system above the cmc are higher than those of single AP432 or C₁₇H₃₃COONa solutions. This is probably due to a looser pack of the molecules within micelles for the AP432/C₁₇H₃₃COONa mixture, which is also consistent with the results obtained from TEM observations. For comparison, the interaction between a commercially available linear PEO-PPO-PEO copolymer (Pluronics L64) and C₁₇H₃₃COONa was also studied. All experimental results give clear evidence that the interaction between L64 and C₁₇H₃₃COONa is different from that between AP432 and C₁₇H₃₃COONa.     

A structure theorem for abelian quasi-ordered groups

We introduce a notion of compatible quasi-ordered groups which unifies valued and ordered abelian groups. It was proved by S.M. Fakhruddin that a compatible quasi-order on a field is always either an order or a valuation. We show here that the group case is more complicated than the field case and describe the general structure of a compatible quasi-ordered abelian group. We then define a notion of Hahn product of compatible quasi-ordered groups and generalize Hahn's embedding theorem to quasi-ordered groups. We also develop a notion of quasi-order-minimality and establish a connection with C-minimality, thus answering a question of F. Delon. Finally, we use compatible quasi-ordered groups to give an example of a C-minimal group which is neither an ordered nor a valued group.