Characteristic length of dynamic glass transition based on polymer/clay intercalated nanocomposites

The glass transition is an old physical problem. It has been accepted that there is a cooperatively rearranging region related to dynamic heterogeneity when temperature approaches the glass transition. However, there is no consensus with the characteristic length and the size of cooperatively rearranging region. This paper first employs the clay gallery in polymer/clay intercalated nanocomposites as a confined two-dimensional (2D) space to assess the characteristic length of dynamic glass transition. The five kinds of clays with different d-spacings were used to investigate the confinement effect. Theoretical calculation based on Donth's formula suggests that the characteristic lengths of polyol and polyol-based polyurethane are ∼3.20 and ∼1.45 nm, respectively. The experimental results agree with theoretical prediction using Donth's formula. The characteristic length varies with polymer types.     

含刚性链节和脲端基聚醚增韧剂改性环氧树脂的研究———反应活性及力学性能

合成了一系列既含环氧丙烷聚醚（ＰＰＧ）柔性间隔基、又含刚性介晶结构单元的端脲基活性改性剂（ＬＣＥＵＰＰＧ），并对其改性环氧树脂Ｅ ５１／双氰双胺（Ｅ ５１／ｄｉｃｙ）体系的固化反应活性、改性剂含量对增韧体系动态力学性能及冲击性能的影响进行了研究．结果表明：ＬＣＥＵＰＰＧ的加入对固化体系具有明显的增韧作用，冲击强度提高了３～７倍；其对Ｅ ５１／ｄｉｃｙ固化反应具有明显的促进作用，可使固化反应表观活化能（Ｅａ）降低５０～７０ＫＪ／ｍｏｌ、固化温度降低３０～４０℃；体系的玻璃化转变温度（Ｔｇ）略有下降，但模量基本不降低或略有升高；β 转变向低温方向移动．     

蓖麻油—甲基丙烯酸甲酯AB交联聚合物的研究

将蓖麻油与顺丁烯二酸酐反应,合成端乙烯基蓖麻油,再与甲基丙烯酸甲酯共聚,制得了组成不同的一系列AB交联聚合物,研究了它们的动态性能、力学性能和形态结构与组成的关系.     

双组份网状共聚物的动态力学性质

本文研究了端乙烯基聚氨酯预聚物(VTPU)同乙烯类单体甲基丙烯酸甲酯(MMA)、苯乙烯(St)、醋酸乙烯酯(VAc)、和甲基丙烯酸丁酯(BMA)聚合得到的双组份网状共聚物(BCN′s)的动态力学性能及形态结构。四种BCN′s试样两组份在动态力学谱上均有半相容的特征。体系的交联密度增大,混合熵增加,相容性改善,试样中可溶性组份含量随BCN′s的组成而变化。溶胶组份可改善体系中两组份的相容性。     

The preparative dynamic density gradient method

In this work the development of a new ultracentrifugation method is described. The preparative density gradient method (PDDG) allows the fractionation of colloidal systems according to the density of their components. The fractions—collected separately—can be subjected to further investigations with any appropriate physical or analytical method. The particle density of a colloidal system is a very valuable information that can be used in many ways. Here for the first time a method is presented that could make the access to that information much easier for laboratories throughout the world. The preparative dynamic density gradient is performed in a preparative ultracentrifugation tube by layering heavy water under a sample that is dispersed or dissolved in water. The water and heavy water molecules undergo a fast diffusion process finally leading to a homogeneous solvent mixture. While reaching this equilibrium the water–heavy water concentration varies over the cell radius. Thus a density gradient is built up. Fractions of the sample will move to the radial position where their densities are matched. They can then be collected separately. In this work basic experiments and results that lead to the development of the PDDG will be presented. Calculations based on basic ultracentrifugation theory confirm the described experimental findings. An example will demonstrate the problem solving capability of this new method.     

蓖麻油聚氨酯和乙烯类聚合物互穿网络材料的生成特点及其动态力学性能

研究蓖麻油聚氨酯/取代乙烯共聚物的互穿网络物(IPN)的生成特点指出,其中取代乙烯游离基共聚的氧化还原引发剂组份-过氧化苯甲酰或二甲基苯胺都能加速聚氨酯网络(Pu)的生成。反应温度在 30℃以上蓖麻油也能参与游离基共聚。蓖麻油不仅与TDI反应生成Pu网络,而且也有小部分参与取代乙烯共聚物长枝链的形成。Pu网络的形成较长枝链的生成为快。生成Pu网络时所放出的热促进取代乙烯与少量蓖麻油的双键共聚,最后生成的IPN不溶于甲苯。这表明生成的是接技的半IPN,而不是单纯的半IPN。动态力学研究指出,包含聚苯乙烯或聚甲基丙烯酸甲酯的这种IPN呈现二个T_g,而只包含聚丙烯腈的仅一个T_g,说明后一IPN中相容性较好,有较多的分子混合。随着聚氨酯与聚取代乙烯的比例减少,二个T_g间的差距减少,而较高温度的T_g随取代乙烯共聚物中丙烯腈含量增加而变小。     

Supercooled water. Considerations about the system organization of liquid water

Summary Supercooled water shows increasing values in heat capacity, free energy difference (in relation to ice) and compressibility as the temperature is lowered, whereas the density is decreased. After careful consideration of the boundary conditions, as they are required for the preparation of supercooled water, the reorganizations within the liquid were investigated and the changes in differentiations examined. Different groups of water molecules are distinguished, namely those at the interface, around dissolved gas molecules, around hydrophilic solutes and the vast majority of the remaining water molecules. It is emphasized that all of these groups are required for the existence of liquid water. Their continuous interrelations are described by the introduction of hierarchic levels, as they are characteristic for a system organization.The highest hierarchic level is that of the interface, the forces of which regulate and control the exchange of matter and energy both with the environment and within the liquid phase. Subordinated to this level is that of the dissolved gas molecules and their surrounding water molecules. In both of these levels the dynamic aspects are highly developed. Subordinated to this level is that of the hydrophilic solutes and their surrounding water molecules. Their unavoidable presence in liquid water is evidenced by the self-ionization equilibrium. The lowest level is that of all of the other water molecules, which provides some kind of more static boundary conditions for the exercise of the better developed dynamic features of the higher levels.In order to obtain supercooled water, the dynamic features must be improved in the higher hierarchic levels, whereas in the lower levels the more static features should remain as small as possible. The former is achieved by certain cooling modes, by increased surface area, by hydrophobic environment and by increasing gas concentration in the liquid. On the other hand, the concentration of hydrophilic solutes must be minimized (the purity of water enhanced). The metastable state is dynamically better maintained, the better the system organization is developed. The state of supercooled water approaches that of optimal system organization in the temperature range between –20° and –30°C.

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Unterkühltes Wasser. Betrachtungen über die Systemorganisation von flüssigem Wasser

Zusammenfassung In unterkühltem Wasser nehmen die Wärmekapazität, die Differenz der freien Enthalpie in bezug auf Eis und die Kompressibilität mit sinkender Temperatur zu, während die Dichte abnimmt. Unter Berücksichtigung aller Randbedingungen, unter denen Wasser unterkühlbar ist, wurden die Reorganisationen innerhalb der Flüssigkeit untersucht. Die Eigenschaften von Wassermolekülen an der Phasengrenzfläche, in der Umgebung von Gasmolekülen, in der Umgebung hydrophiler Teilchen und der großen Zahl der übrigen Wassermoleküle sind unterschiedlich. Ihre kontinuierlichen Wechselbeziehungen werden durch Einführung hierarchischer Ebenen beschrieben, wie sie für eine Systemorganisation charakteristisch sind.Die höchste hierarchische Ebene ist diejenige der Moleküle an der Phasengrenzfläche, deren Kräfte den Austausch von Materie und Energie sowohl mit der Umgebung als auch innerhalb der flüssigen Phase regulieren und kontrollieren. Dieser Ebene untergeordnet ist diejenige der gelösten Gasmoleküle und der sie umgebenden Wassermoleküle. In diesen beiden Ebenen sind die dynamischen Aspekte hoch entwickelt. Dieser Ebene nachgeordnet ist diejenige der die hydrophilen Bereiche umgebenden Wassermoleküle. Die niedrigste Ebene ist diejenige aller anderen Wassermoleküle, welche eine Art statischer Randbedingungen für die Ausübung der in den höheren Ebenen besser entwickelten dynamischen Aspekte bieten.Um unterkühltes Wasser zu erhalten, müssen in den höheren hierarchischen Ebenen die dynamischen Eigenschaften verbessert werden, während in den unteren hierarchischen Ebenen die Differenziertheit so klein wie möglich bleiben soll. Ersteres wird durch Vergrößerung der Oberfläche, bestimmte Abkühlungsbedingungen, hydrophobe Umgebung und durch zunehmende Konzentration an gelösten Gasen erreicht, letzteres durch Erhöhung der Reinheit (Minimisierung der Konzentration hydrophiler Teilchen). Der metastabile Zustand wird umso besser dynamisch aufrechterhalten, je besser seine Systemorganisation entwickelt ist. Der Zustand des unterkühlten Wassers kommt der optimalen Systemorganisation im Temperaturbereich zwischen –20° und –30°C am nächsten.

     

Mono- and bis-(2-dimethylaminoethyl)tetramethylcyclopentadienyl zirconium(IV) complexes: synthesis and structural studies in crystalline state and in solutions

A novel half-sandwich Zr(IV) complex [η⁵:η¹-N-C₅(CH₃)₄CH₂CH₂N(CH₃)₂]ZrCl₃ (6) together with zirconocene dichlorides [η⁵-C₅(CH₃)₄CH₂CH₂N(CH₃)₂][η⁵-C₅(CH₃)₅]ZrCl₂ (4) and [η⁵-C₅(CH₃)₄CH₂CH₂N(CH₃)₂]₂ZrCl₂ (5) have been prepared. Complex 6 has been isolated and characterized in three different forms, namely, as an adduct with THF 6a, an adduct with tetrahydrothiophene 6b, and a solvent-free form 6c. Molecular structures of complexes 4, 6b, and 6c have been established by X-ray diffraction analysis. Complex 6c has been shown to be a monomeric solvent-free half sandwich Zr(IV) complex. The dynamic behavior of complex 6a in a non-solvating medium (an equilibrium between 6a and 6c along with a degenerate interconversion of the Zr-C_cp-CH₂-CH₂-N(CH₃)₂-(Zr) pseudo-five-member metallacycle) have been studied by the variable-temperature ¹H and ¹³C{¹H} NMR spectroscopy. The activation parameters for the degenerate five-member cycle interconversion have been elucidated.     

聚氨酯弹性体相分离程度的研究

热塑型聚氨酯弹性体(TPUE)的动态力学性能和热性能研究已有许多报导,但多集中于弹性体的链结构及其组成等方面,本文则侧重于研究聚醚氨酯(ET)和聚酯氨酯的相分离过程及其程度,考察硬段含量(W_h)和软段分子量(M_(n·3)等因素对微相结构的影响。     

Selective determination of airborne hexavalent chromium using inductively coupled plasma mass spectrometry

A new method for determining ultra-trace levels of hexavalent chromium in ambient air has been developed. The method involves a 24-h sampling of air into potassium hydroxide solution, followed by silica gel column separation of chromium (VI), then preconcentration by complexation and solvent extraction. The chromium (VI) complex was dissolved in nitric acid. The resultant chromium ions were determined by inductively coupled plasma mass spectrometry (ICP–MS) using a dynamic reaction cell (DRC) with ammonia as the reactive gas to reduce polyatomic interferences. The interconversion of chromium in potassium hydroxide solution and air sample matrix were investigated under ambient conditions. It was found that there was no conversion of chromium (VI) into chromium (III) species. However, it was observed that some chromium (III) species were converted into chromium (VI) species. For a KOH solution containing 100 μg l⁻¹ of chromium (III) species, the rate of conversion was found to be 3% after 24 h exposure, 8% after 48 h, 10% after 72 h and no further conversion was observed thereafter. However, in a solution containing air sample matrix, 9.3% of chromium (III) converted to chromium (VI) within 6 h, and during the course of a 11-day exposure period, 13% (range 8–17%) of chromium (III) converted to chromium (VI). The method detection limit (MDL) for chromium (VI) in potassium hydroxide solution (0.025 M) was found to be 2×10⁻² μg l⁻¹. This is equivalent to 0.2 ng m⁻³ (for 23 m³ air sampled into 200 ml of KOH solution over a 24-h period). The recovery of spiked chromium (VI) from solutions containing air sample matrix was 95±9% (n=8). Matrix related interferences were estimated to be less than 10% based on recovery studies. The concentration of airborne chromium (VI) in Sydney residential areas was found to be less than 0.2 ng m⁻³, however, in industrial areas the concentrations ranged from 0.2 to 1.3 ng m⁻³ using this analytical procedure.