Effect of lithium-sodium mixed-alkali on phase transformation kinetics in Er3+/Yb3+ co-doped aluminophosphate glasses

Er3+ doped aluminophosphate glasses with various Na2O/Li2O ratios were prepared at 1250 degrees C using a silica crucible to study mixed alkali effect (MAE). The effect of relative alkali content on glass transition temperature, crystallization temperature and thermal stability were investigated using differential scanning calorimetry (DSC). In addition, apparent activation energies for crystallization, E, were determined employing the Kissinger equation. The effect of Al2O3 content on the magnitude of MAE was also discussed. No mixed-alkali effect is observed on crystallization temperature. (c) 2006 Elsevier B.V. All rights reserved.

Suppression of phase separation in PC/PMMA blend film by thermoset oligomer

Phase separation of bisphenol A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) thin blend film is suppressed by addition of solid epoxy oligomer. Epoxy has strong intermolecular interactions with both PC and PMMA, while PC and PMMA are quite incompatible with each other. Consequently, phase separation in the PC/PMMA blend film pushes epoxy to the interface; at the same time, PC and epoxy react readily at the interface to form a cross-linking structure, binding PMMA chains together. Therefore, the interface between PC and PMMA is effectively reinforced, and the PC/PMMA thin blend film is stabilized against phase separation. On the other hand, only an optimal content of epoxy (i.e., 10 wt %) can serve as an efficient interfacial agent. In contrast to the traditional reactive compatibilization, here we observed that the cross-linking structure along the interface is much more stable than block or graft copolymers. Atomic force microscopy (AFM) is used to characterize the morphological changes of the blend films as a function of annealing time. Two-dimensional fast Fourier transform (2D-FFT) of AFM data allows quantitative investigation of the scaling behavior of phase separation kinetics.

Preparation of methyl tert-butyl ether (MTBE) over heteropoly acids immobilized on activated carbon (HPA/C) in the vapor phase

Heteropolyacids (HPAs) supported on the activated carbon (SiW12/C and PW12/C) have been used to study the formation of methyl tert-butyl ether (MTBE). Compared to the conventional commercial catalysts, Amberlyst-15 resin and HZSM-5, HPAs supported catalysts have been proved to have much higher catalytic activity under lower temperature, especially selectivity to MTBE is up to 100%. It may be due to the high acid strength of HPAs as well as the specialty of heteropolyanion.

Domains in ferroelectric nanodots

Almost free-standing single crystal mesoscale and nanoscale dots of ferroelectric BaTiO(3) have been made by direct focused ion beam patterning of bulk single crystal material. The domain structures which appear in these single crystal dots, after cooling through the Curie temperature, were observed to form into quadrants, with each quadrant consisting of fine 90 degrees stripe domains. The reason that these rather complex domain configurations form is uncertain, but we consider and discuss three possibilities for their genesis: first, that the quadrant features initially form to facilitate field-closure, but then develop 90 degrees shape compensating stripe domains in order to accommodate disclination stresses; second, that they are the result of the impingement of domain packets which nucleate at the sidewalls of the dots forming "Forsbergh" patterns (essentially the result of phase transition kinetics); and third, that 90 degrees domains form to conserve the shape of the nanodot as it is cooled through the Curie temperature but arrange into quadrant packets in order to minimize the energy associated with uncompensated surface charges (thus representing an equilibrium state). While the third model is the preferred one, we note that the second and third models are not mutually exclusive.

多相聚合物体系相分离动力学的理论和模拟

本文提出了将自洽场理论与多相流格子Boltzmann方法相结合的模型，并从该模型出发推导出了描述动量守恒的Navier-Stokes方程和扩散方程，验证了模型理论上的正确性。应用此模型，对聚合物的相分离过程进行了模拟。 首先证实了本模型最终能够得到正确的热力学平衡结果。对于高分子共混物和嵌段共聚物相分离的动力学过程。在分相各个阶段，对高分子共混物和嵌段共聚物都进行了验证。 其次，应用所提出的格子Boltzmann模型，分别对二元聚合物共混物和二嵌段共聚物的相分离后期相区增长过程进行了研究。 最后，通过模型的进一步扩展，实现了对具有复杂结构的嵌段共聚物和复杂共混物的模拟。

PMMA/SAN共混物薄膜表面相分离动力学的原位AFM研究

本论文主要借助原子力显微镜（AFM）、X-射线光电子能谱（XPS）等实验手段，纳米尺度上在线原位地研究了高温临界组成PMMMA/SAN（50／50，w／w）共混薄膜体系，分析并探讨了此共混薄膜表面相分离及其超薄膜体系的润湿／去润湿和相分离行为。首先，从敲击式AFM中相位图的成像原理出发，建立了一个高温下用原位AFM定性鉴别不同聚合物的纳米尺寸微区的方法，即：先在基底（硅）上铺展一层非常平坦的单一组分（SAN）薄膜，再在此千膜上，通过旋涂由选择性溶剂（冰醋酸）配制的另一组分（PMMA）的极稀溶液，使之不能形成一层连续的完整膜，最后在高温（175℃）下用敲击模式的原子力显微镜（TM-AFM）检测相位图随退火时间的变化。得到在175℃的相位图中，PMMA富相比SAN的富相显得更暗，这为后续工作提供了定性鉴别相区的方法。其次，高温下用原位AFM研究了PMMA/SAN薄膜表面相分离过程，在线观察了相分离的归并过程，定量地得到了临界相分离温度，并给出了特征波矢对时间依赖关系的标度指数，划分了相分离动力学演变的不同阶段。对于膜厚约为130nm的体系，表面相分离的临界温度大约为165℃，其表面相分离的特征波矢与时间的标度关系q+（t）-t-n，在整个实验时间内，随时间的演变过程中，显示了两个不同的指数变化区，即前期很慢的n=0.13和后期的n＝1／3。0.13的指数关系可能是由于表面聚合物链的几何受限及表面富集相把部分新生成的另一相覆盖所致，1／3的指数关系可以认为是由普遍的Brownian扩散所致。而对于膜厚为50曲的此组成共混薄膜，得到的标度关系与C汕n线性理论吻合得非常好的Spinodal Deposition（SD）表面相分离的初期，即n＝0，这是由于降低膜厚 增加了共混物的相容性，提高了临界温度，从而减缓了相分离过程，使得在我 们观测的时间范围内更易观察到表面相分离的初期。再次，用阶梯式降温的好M和XPS，发现了PMMA/SAN体系原位和离位实验结果存在巨大差别的主要原因之一—润湿温度的存在。对PMMA/SAN（50／50，w／w，-130nm）共混薄膜体系，原位AFM的退火和准淬火实验表明， 虽然在高温和室温、真空和常态、原位和离位，相分离的聚合物共混薄膜表面 形貌变化不大，但是表面物理性质却有很大的区别。原位XPS实验表明，未经 任何处理的样品在185℃退火时，很快在离表面很薄的下面形成一层PMMA含 量远低于本体值的薄层，之后最表面的PMMA也往本体迁移，直至表面SAN 的含量远高于它的本体值。对已在175℃退火20hr的此样品，逐渐降温退火过 程的原位XPS表明，当退火温度降至145oC时，样品表面几乎完全被PMMA覆盖，很好地验证了Conlposto等提出的润湿温度的假设，即对此体系，润湿温 度是原位和离位存在巨大的差异的主要因素之一，这与原位AFM的实验结果也，存在很好的一致性。最后，高温下原位观察了硅基底上PMMA/SAN超薄膜（膜厚-Rg）的去润湿、相分离过程和PMMA在基底上的润湿过程，以及云母基底上的该体系高温下的稳定润湿行为。以硅为基底的PMM刀sAN共混超薄膜在155”c下发生了类 似sPinodal dewetting的去润湿，其原因可能是在垂直于基底的浓度梯度引起的表面组成的涨落，对这种去润湿的动力学还进行了探讨。以硅为基底的PMMA/SAN共混超薄膜在175℃下不仅发生了类似spinodal dewetting的去润 湿，而且还发生了去润湿液滴内部的相分离以及相分离析出的PMMA润湿硅基底的过程，提出了一个简单的模型描述了这种复杂的过程。此外，还研究了不同基底对此共混超薄膜体系的润湿行为进行了研究，以云母为基底的此共混体系在175℃下长时间内是稳定的，其原因可能是云母与PMMA和SAN均有很强的作用力，足于补偿聚合物链在构象嫡上的损失。

PREDICTION OF THE GIBBS ENERGY OF ION TRANSFER ACROSS THE WATER NITROBENZENE INTERFACE USING 3 NEW TOPOLOGICAL INDEXES

Correlation analysis of the standard Gibbs energy for a series of tetraalkylammonium ions, protonated substituted ethylenediamine derivatives and protonated aromatic amine derivatives using three new topological indices Ax1, Ax2 and Ax has been studied. T

Phase unwrapping based on branch cut placing and reliability ordering

A new 2-D quality-guided phase-unwrapping algorithm, based on the placement of the branch cuts, is presented. Its framework consists of branch cut placing guided by an original quality map and reliability ordering performed on a final quality map. To improve the noise immunity of the new algorithm, a new quality map, which is used as the original quality map to guide the placement of the branch cuts, is proposed. After a complete description of the algorithm and the quality map, several wrapped images are used to examine the effectiveness of the algorithm. Computer simulation and experimental results make it clear that the proposed algorithm works effectively even when a wrapped phase map contains error sources, such as phase discontinuities, noise, and undersampling. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Phase unwrapping based on branch cut placing and reliability ordering

A new 2-D quality-guided phase-unwrapping algorithm, based on the placement of the branch cuts, is presented. Its framework consists of branch cut placing guided by an original quality map and reliability ordering performed on a final quality map. To improve the noise immunity of the new algorithm, a new quality map, which is used as the original quality map to guide the placement of the branch cuts, is proposed. After a complete description of the algorithm and the quality map, several wrapped images are used to examine the effectiveness of the algorithm. Computer simulation and experimental results make it clear that the proposed algorithm works effectively even when a wrapped phase map contains error sources, such as phase discontinuities, noise, and undersampling. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Phase mapping of domain kinetics in lithium niobate by digital holographic interferometry

The phase mapping of domain kinetics under the uniform steady-state electric field is achieved and investigated in the LiNbO3 crystals by digital holographic interferometry. We obtained the sequences of reconstructed three-dimensional and two-dimensional wave-field phase distributions during the electric poling in the congruent and near stoichiometric LiNbO3 crystals. The phase mapping of individual domain nucleation and growth in the two crystals are obtained. It is found that both longitudinal and lateral domain growths are not linear during the electric poling. The phase mapping of domain wall motions in the two crystals is also obtained. Both the phase relaxation and the pinning-depinning mechanism are observed during the domain wall motion. The residual phase distribution is observed after the high-speed domain wall motion. The corresponding analyses and discussions are proposed to explain the phenomena.