U.S.-Japan Cooperative Research: Study of Polymers by Positron Annihilation

美日合作研究：通过正电子湮灭研究聚合物

• 批准号: 8915060
• 负责人: John McGervey
• 金额: $ 2.68万
• 依托单位: Case Western Reserve University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1990
• 资助国家: 美国
• 起止时间: 1990-04-01 至 1993-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8915060&HistoricalAwards=false
• 关键词: U.S.; Japan; Cooperative; Research; Study

This award will enable Professor John D. McGervey, Department of Physics, Case Western Reserve University, and U.S. colleagues to collaborate with Professor Yusuke Ujihira, Engineering Research Institute, The University of Tokyo, and other Japanese researchers in a study of polymers by the technique of positron annihilation. The basis of this technique is the fact that the lifetime of a positron in a variety of materials has been found to be dependent upon the electron density in its surroundings. In regions of relatively low electron density--in holes or defects in a solid, for example--the lifetime is measurably longer (though still measured in trillionths of a second) than in other, higher density regions. The lifetime is measured by observing the gamma ray which signals the creation of a positron, followed by a second gamma ray which appears when the positron is annihilated. In polymers, the longer lifetime is thought to be the result of the formation of an "atom" of ortho-positronium (o-Ps), which is more stable toward annihilation by an electron than is a positron itself. The lifetime of positronium is thus a measure of the size of the free- volume element ("hole") in which it finds itself. In the case of polymers the o-Ps appears to be formed or trapped in the free- volume elements that exist between the strands of polymer molecules. The greater the number and volume of such elements, the greater is the probability of forming o-Ps. From the measured positron lifetime distribution in a polymer sample it is possible to partially characterize the sample in terms of the size distribution of its free-volume elements. Such information is useful in studies aimed at understanding the relationship between free volume and such polymer properties as viscosity, elasticity, and gas permeability; the change (decrease) in free volume with polymer aging; and the response of polymers to variables such as temperature and pressure. The cooperating scientists have had considerable experience in the positron lifetime technique. In this cooperative effort they plan to pursue further its application to polymer studies by developing standardized methods for sample preparation and characterization, as well as procedures for dealing with possible sources of systematic error. The technique will be applied to various polymers, including some that may be used in advanced engineering plastics.

这一奖项将使教授约翰D。McGervey，部门 凯斯西储大学物理系和美国同事， 与Yusuke Ujihira教授合作，工程研究 研究所、东京大学和其他日本研究人员 用正电子湮没技术研究聚合物。 这种技术的基础是， 正电子在各种材料已被发现是依赖于 周围的电子密度。 的区域中 相对较低的电子密度--在固体中的空穴或缺陷中， 例如，寿命长得多（尽管仍然 以万亿分之一秒为单位测量）， 地区 寿命是通过观察伽马射线来测量的， 发出正电子产生的信号，然后是第二个伽马射线 当正电子湮灭时就会出现 在聚合物中， 更长的寿命被认为是形成一种 正电子偶素（o-Ps）的“原子”，它对 比正电子本身更容易湮灭。 的 正电子素的寿命是衡量自由电子素大小的尺度。 体积元素（“孔”），它发现自己。 的情况下 聚合物的o-Ps似乎形成或捕获在自由- 存在于聚合物分子链之间的体积元。 这些元素的数量和体积越大， 形成o-Ps的概率。 从测得的正电子 聚合物样品中的寿命分布， 根据其粒度分布表征样品 自由体积元素。 这些信息对于旨在 在理解自由体积和 聚合物特性如粘度、弹性和透气性; 自由体积随聚合物老化的变化（减少）;以及 聚合物对温度和压力等变量的响应。 合作的科学家在这方面有着丰富的经验， 正电子寿命技术 在这次合作中，他们计划 进一步追求其应用于聚合物研究， 用于样品制备和表征的标准化方法， 以及处理可能的系统污染源的程序， 错误. 该技术将应用于各种聚合物，包括 有些可用于先进的工程塑料。