Viscoelastic properties of amorphous polymers 3: low molecular weight poly(methylphenylsiloxane)

By making creep and recoverable creep measurements of a nearly monodisperse low molecular weight poly(methyl phenyl siloxane) sample, we have found on decreasing temperature towardsT _g that there is continuously a change in the viscoelastic spectrum concomitant with a decrease of the steadystate recoverable compliance. This behavior is exactly the same as previously observed in low molecular weight poly(styrene), proving that this spectacular anomaly in the viscoelasticity of low molecular weight polymers is general and deserves an explanation. Photon correlation spectroscopic measurements performed on the same sample have extended the observation of the viscoelastic response to shorter times and the result corroborates the trend of variation established by the creep data.Dedicated to Prof.Dr. E. W. Fischer on his 65th Birthday. Prof.Dr. Fischer is known for his valuable contribution to fosterine, international collaboration of research in polymer science. This work is an example of his contribution because it would not be possible without him bringing us together. One of us (KLN) would like to take this opportunity to thank Prof. Dr. Fischer for his unwaiving support of the 1st (Crete) and the 2nd (Alicante) International Discussion Meeting on Relaxations in Complex Systems     

有关力学谱和内耗工作的综合与回顾

本文广泛地收集了有关内耗，力学谱，超声衰减方面的专著及会议文集。反映了20世纪在此领域的英文，俄文出版的书籍。也列出了历次国际会议及前苏联，乌克兰，中国的国内会议。文中包括了点缺陷，电，声子，位错，晶界，电畴等诸方面在内的内耗与力学谱工作。     

临床试验(Ⅱ)

在本文的第Ⅰ部份，涉及了临床试验的内涵、研究中的偏性、困难与临床试验设计的进展．第Ⅱ部份主要涉及分析中的一些重要问题，其中包括：５，生存质量的测定；６，病人的依从性； ７， Ｍｅｔａ分析．     

Creep of composites with a porous fibre/matrix interface under variable loading

A micromechanical model of island-type fibre/matrix interface is described and experimental data are represented and analysed. Changes in the interface strength during a cycle loadings and, correspondingly, changes in the creep resistance of a composite due the island-like scheme of the fibre/matrix interface are described.     

钇对Ti-1100高温钛合金热稳定性和蠕变行为的影响

量了Ｔｉ１１００和Ｔｉ１１００／０１％Ｙ（质量分数）高温钛合金在６００℃／１００ｈ空气中暴露后的拉伸性能及在６００℃／１５０ＭＰａ／１００ｈ条件下的蠕变性能，利用透射电镜观察了合金室温及蠕变后的组织。结果表明，Ｔｉ１１００合金加入０１％的Ｙ后，由于原始β晶粒得到细化，明显改善了其热稳定性；固溶在基体中的硅原子阻碍位错滑移和攀移，使蠕变中的回复过程难于实现；稀土还抑制α２相的长大，所形成的氧化物也阻碍位错的运动。这些均有利于提高Ｔｉ１１００合金的抗蠕变性能。     

用TMS—2型热机分析仪测量热释蠕变

对已经商品化的Perkin-Elmer TMS-2型热机分析仪进行改进,用来测量聚合物材料的热释蠕变行为。按照7SCr分步加载的程序,用弯曲法测量了-83～300℃温度范围内低密度聚乙烯的玻璃化转变松弛过程,并从TSCr谱上计算其相应的分子参数,实验结果与用扭转的TSCr方法所得结果相等,因此这是一种研究聚合物材料松弛行为的方便可行的技术。     

Multi-mechanism models: Present state and future trends

The paper gives a review of the main features introduced in the multi-mechanism models, of the present possibilities and of further developments.In the two last decades, various materials and mechanical effects were studied using multi-mechanism model types. Particular attention was given to the possible link between the mechanism definitions and the physical deformation sources. The main results of these works are first recalled. Propositions of future development for the multi-mechanism models are finally given.     

Anionic Conduction in Blends of Poly(Pyridinium Ethyl Methacrylate Perchloride) and Poly[Oligo(Oxyethylene) Methacrylate-Co-Acrylamide]

Abstract

Blends of poly(pyridinium ethyl methacrylate perchloride) and poly[oligo(oxyethylene) methacrylate-co-acrylamide] were prepared, and the ionic conductivity and mobility of the blends were investigated. Results indicate that both the transference of perchlorate anion and the dissociation of the polymeric salt in the comblike polyether obey the thermoactivation mechanism, and that the perchlorate anion in the blends is free.     

Investigation of Viscoelastic Properties of Amorphous Selenium near Glass Transition Using Depth‐Sensing Indentation

Abstract

New procedures involving depth‐sensing indentation are used to measure the submicron scale elastic modulus, hardness, viscosity, and activation energy and volume for creep of amorphous selenium below glass transition. The accurate measurement of Young's modulus in a highly viscoelastic situation using depth‐sensing indentation remains a challenge, and a creep correction procedure is employed here to measure the modulus. The measured Young's modulus exhibits a strong decreasing trend from ～10 GPa to 4.4 GPa as temperature increases from ～302 K to 309 K, in reasonably good agreement with bulk behavior. Two new procedures are also proposed here to measure the viscosity. The measured shear viscosity decreases from ～1×10¹² Pa‐s to ～2×10¹⁰ Pa‐s when the temperature increases over the same range, and the variation with temperature is found to obey an Arrehnius rate equation. The activation energy for the viscous creep process is found to be ～463 kJ/mol. Both the viscosity and the activation energy are lower than the bulk values, and this is thought to be due to the much higher stress levels of over 200 MPa involved in the nanoindentation experiments here. The apparent activation volume exhibits a rising trend from 1.04×10^?31 to 2.35×10^?30 m³ over the same temperature range.     

Measurement of viscoelastic properties for polymers by nanoindentation

A new method has been proposed and verified to measure the viscoelastic properties of polymers by nanoindentation tests. With the mechanical response of load–displacement curves at different loading rates, the parameters of creep compliance and relaxation modulus are calculated through the viscoelastic contact model. Dynamic thermomechanical analysis (DMA) tests are conducted to compare the results by the proposed technique. The results show that the correlation coefficients between DMA tests and the new method are above 0.9 in the entire range, which verified the feasibility of the method. The loading curves fitted by the model are identical to the experimental curves within the discrete points and so it shows that this technique is more suitable for general linear viscoelastic materials. Numerical creep tests are carried out to examine the effectiveness of the proposed method by input the Prony series calculated by the three-element Maxwell model and the viscoelastic contact model. The good agreement shows that the proposed technique can be applied in practice.