聚氨酯硬链段球晶生长与软硬链锻混容性的关系

线型可溶性聚氨酯的硬链段结晶难以长成球晶 ,然而本实验室已经证明即使从熔体结晶硬链段也是能够长成球晶的 .研究了聚酯与聚醚型聚氨酯硬链段长球晶的规律 ,并发现聚氨酯硬链段长球晶的难易与聚氨酯软硬链段混容性密切相关 .动态力学分析 (DMA)与示差扫描量热 (DSC)实验表明聚ε 已内酯 (PCL)、聚已二酸丁二醇酯 (PTMA)、聚四氢呋喃 (PTMO)及聚环氧丙烷 (PPO)型聚氨酯的软硬链段混容性从前至后递减 .从熔体退火结晶时 ,聚氨酯硬链段长成球晶的退火温度范围是有限的 ,软硬链段混容性越好 ,聚氨酯硬链段能长成球晶的温度范围越窄 ,所需长的时间越长 .聚氨酯硬链段长球晶的下限温度取决于软硬链段间所存在的氢键作用 ,聚氨酯硬链段长球晶的上限温度与软硬链段混容性直接相关 .     

Multi-critical tensor models and hard dimers on spherical random lattices

Random tensor models which display multi-critical behaviors in a remarkably simple fashion are presented. They come with entropy exponents γ=(m−1)/m$\gamma =(m-1)/m$, similarly to multi-critical random branched polymers. Moreover, they are interpreted as models of hard dimers on a set of random lattices for the sphere in dimension three and higher. Dimers with their exclusion rules are generated by the different interactions between tensors, whose coupling constants are dimer activities. As an illustration, we describe one multi-critical point, which is interpreted as a transition between the dilute phase and a crystallized phase, though with negative activities.     

Structural transformations and magnetic properties of Fe60Pt15B25 and Fe60Pt25B15 nanocomposite alloys

Structural and magnetic properties of two rapidly solidified and post-annealed Fe₆₀Pt₁₅B₂₅ and Fe₆₀Pt₂₅B₁₅ alloys are compared. The as-quenched Fe₆₀Pt₁₅B₂₅ ribbon was fully amorphous whereas in the Fe₆₀Pt₂₅B₁₅ alloy the amorphous phase coexists with an fcc FePt disordered solid solution. Differential scanning calorimetry curves of both alloys reveal a single exothermal peak with onset temperatures of 873 and 847 K for Fe₆₀Pt₁₅B₂₅ and Fe₆₀Pt₂₅B₁₅, respectively. Magnetically hard, tetragonal ordered L1₀ FePt and magnetically soft Fe₂B nanocrystalline phases were formed due to the annealing of the alloys, as indicated by X-ray diffraction and Mössbauer spectroscopy measurements. Two-phase behavior was detected in the temperature dependence of magnetization of the annealed samples. A magnetic hardening was observed for all annealed ribbons. Magnetic properties of the annealed alloys, studied by hysteresis loop measurements, were related to the differences in the relative fractions of the hard and soft magnetic phases calculated from Mössbauer spectra. The alloy with 25 at% Pt exhibits better hard magnetic properties (H_c=437 kA/m, M_r/M_s=0.74) than the alloy with smaller Pt content (H_c=270 kA/m, M_r/M_s=0.73) mainly due to the larger abundance of the ordered tetragonal FePt phase.     

Investigation of kinetics and thermodynamics of DNA hybridization by means of 2-D fluorescence spectroscopy and soft/hard modeling techniques

Reversible hybridization reaction plays a key role in fundamental biological processes, in many laboratory techniques, and also in DNA based sensing devices. Comprehensive investigation of this process is, therefore, essential for the development of more sophisticated applications. Kinetics and thermodynamics of the hybridization reaction, as a second order process, are systematically investigated with the aid of the soft and hard chemometric methods. Labeling two complementary 21 mer DNA single strands with FAM and Texas red fluorophores, enabled recording of the florescence excitation−emission matrices during the experiments which led to three-way data sets. The presence of fluorescence resonance energy transfer in excitation and emission modes and the closure in concentration mode, made the three-way data arrays rank deficient. To acquire primary chemical information, restricted Tucker3 as a soft method was employed. Herein a model-based method, hard restricted trilinear decomposition, is introduced for in depth analysis of rank deficient three-way data sets. By employing proposed hard method, the nonlinear model parameters as well as the correct profiles could be estimated. In addition, a simple constraint is presented to extract chemically reasonable output profiles regarding the core elements of restricted Tucker3 model.     

聚乙二醇型聚氨酯软硬段对其相变储热性能的影响

以不同分子量的聚乙二醇(PEG)为软段,MDI-BDO为硬段,采用两步法溶液聚合合成一种具有固-固相变储热性能的聚氨酯材料.通过DSC,WAXD等测试手段对体系的软硬段结晶性,微相分离,相变可逆性及循环热稳定性进行研究,结果表明,聚氨酯中硬段的存在对软段结晶有着很大的影响,当软段分子量达到2000或以上时,软段才具有较大的结晶度和熔融相变焓,且硬段含量必须高于一定值才能形成较为完善的物理交联网络以保证材料在发生相变时维持固体状态.同时符合这两个条件的试样能具有较好的固-固相变储热性能.就软段PEG含量及分子量对材料储热性能的影响进行了研究,通过调节软段含量与分子量得到一系列具有不同相变焓和相变温度的聚氨酯固-固相变储热材料.经测试还发现,该材料具备很好的相变可逆性和循环热稳定性,是一类很有开发前景的相变储热材料.     

硬盘抗冲击振动特性的研究进展

硬盘驱动器是计算机最重要的外存储设备.由于硬盘抗冲击振动问题的重要性和复杂性,许多研究者对此问题从各个方面进行了研究.本文从硬盘的基本结构和工作原理入手,介绍了磁头/磁盘系统的静动态特性,分析了影响磁头/磁盘系统性能的重要因素及其原理,并对国内外有关提高硬盘抗冲击振动性能的研究进行了较为系统的回顾和分析,最后阐述了硬盘冲击振动的控制研究,分析了硬盘目前所面临的关键问题及其可能的解决方案.     

Hard sphere colloidal dispersions: Mechanical relaxation pertaining to thermodynamic forces

The complex viscosity of sterically stabilized (hard) silica spheres in cyclohexane has been measured between 80 Hz and 170 kHz with torsion pendulums and a nickel tube resonator. The observed relaxation behaviour can be attributed to the interplay of hydrodynamic and thermodynamic forces. The validity of the Cox-Merz rule is checked.     

Lithium-storage properties of SiO2 nanotubes@C using carbon nanotubes as templates

Silica-based anode material is the most concerned material at present, which has the advantages of good cycle stability, high theoretical specific capacity and abundant reserves. However, silica suffers from inherent low conductivity, severe volume expansion effect and low initial coulombic efficiency, which limits its application in lithium-ion batteries. Nanotubes structure can mitigate the volume expansion during lithiation/delithiation. In this article, silica nanotubes (SNTs) were prepared using carbon nanotubes (CNTs) as a template, and then the uniform carbon layer was coated on their surface by carbonization of citric acid. The hollow structure of nanotubes provides more sites for the insertion of Li⁺ during lithiation and additional channels for Li⁺ migration in the cycles, which improves the electrochemical performance. Conductivity can be enhanced by coating carbon layer. The specific capacity of the composite material is about 650 mAh g⁻¹ at 0.1 A g⁻¹ after 100 cycles. With a specific capacity of 400 mAh g⁻¹ even at 1 A g⁻¹ after 100 cycles. The silica-based material is a competitive anode material for lithium-ion batteries.     

瑞典爱斯泼硬岩实验场地应力研究

爱斯泼 (A..sp o..)硬岩实验场 (HRL)是瑞典拟建的永久储放核废料的场地。实测地应力结果表明, 应力的大小和方位变化较为复杂。通过初步分析认为, 场地附近地应力的变化与断裂构造的发育有关。应用离散元方法, 分别选择平面模型和剖面模型模拟了应力场。模拟结果表明, 地应力的量值和方位在断裂附近均发生明显变化, 且与实测结果较吻合。主应力在断裂附近发生不同程度的偏转, 偏转的幅度与断裂走向和区域应力方向之间的夹角有关。应力的量值在断裂附近也有明显变化。在剖面模型中, 较缓倾角断裂模型的模拟结果最接近实测结果。文中还探讨了断裂带法向刚度和切向刚度的计算方法。