NMR methodologies for measuring correlated structural distributions in oxide glasses

在化学系化学测量和成像计划的支持和材料研究部陶瓷计划的共同资助下，俄亥俄州立大学的菲利普·格兰迪内蒂教授和他的团队正在开发和使用尖端的核磁共振(NMR)工具来探测玻璃的化学性质。虽然世界上大多数玻璃生产集中在窗户和容器上，但对改进的特种玻璃的需求日益增长，这些玻璃已成为广泛的技术应用的关键，如手持电子设备、显示器、光纤、照明玻璃基板、生物玻璃植入物和核废料存储。调整新玻璃成分的性能的一个主要挑战是缺乏关于玻璃结构的可用定量细节，这决定了它们的宏观(大块)性能。核磁共振是唯一适合表征这种结构的方法。格兰迪内蒂教授正在开发复杂的“高维”核磁共振方法，以及对核磁共振数据进行统计分析的新方法，以表征碱和碱土硅酸盐和铝硅酸盐玻璃。这项工作将使人们能够更好地理解导致相分离等现象的特征和玻璃强度等性质。这些新的见解将帮助玻璃科学家和工程师研究下一代特种眼镜。这项工作正在为来自代表性不足群体的学生提供研究机会，部分是通过与伯里亚学院(Berea College)的合作(该学院三分之一的学生来自少数族裔，只允许家庭收入在美国家庭收入最低40%的学生入学)。与康宁公司的科学家和世界各地的其他研究实验室的合作为参与该项目的所有学生提供了与行业和跨国界互动的机会。本项目的重点是利用(1)二维(2D)核磁共振方法分离和关联来自Si-29核屏蔽和O-17核电四极相互作用的各向同性和各向异性的核磁共振频率，(2)分离和关联各向同性和Si-29 J耦合的2D核磁共振方法来确定玻璃中存在的核磁共振光谱参数的定量分布，以及(3)用拉普拉斯逆方法来确定Si-29在包括碱和碱土硅酸盐和铝硅酸盐玻璃在内的多组分硅酸盐玻璃中的核纵向和横向弛豫时间的分布。Graninetti小组正在通过确定核磁共振参数与中短程结构之间的解析关系，寻求特定结构量的定量分布，如形成网络的阴离子物种(QN)的分布、Q3硅非桥氧长度、四面体之间的连接角和距离、四面体内扭曲和阳离子渗流阈值。他们还利用多组分硅酸盐玻璃中Si-29的纵向和横向核弛豫时间分布来识别玻璃中的相分离，并深入了解相分离区域的组成和结构。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry and co-funding from the Ceramics Program in the Division of Materials Research, Prof. Philip Grandinetti and his group at the Ohio State University are developing and using sophisticated nuclear magnetic resonance (NMR) tools to probe the chemical properties of glasses. While the majority of world-wide glass production focuses on windows and containers, there is growing demand for improved specialty glasses which have become vital to a large range of technological applications, such as handheld electronic devices, displays, optical fibers, glass substrates for lighting, bio-glass implants, and nuclear waste storage. A major challenge in tailoring the properties of new glass compositions is the inadequacy of available quantitative details about the structure of glasses, which determines their macroscopic (bulk) properties. NMR is uniquely suited for characterization of this structure. Professor Grandinetti is developing both sophisticated "higher-dimensional" NMR methods, and new approaches to statistical analysis of NMR data to characterize alkali and alkaline-earth silicate and aluminosilicate glasses. The work will enable better understanding of features contributing to phenomena such as phase separation and properties such as the strength of glasses. These new insights will help glass scientists and engineers working on the next generation of specialty glasses. The work is providing research opportunities for students from underrepresented groups, in part through a partnership with Berea College (where 1/3 of students are from ethnic minorities and admission is granted only to students whose family income falls within the bottom 40% of U.S. households). Collaborations with scientists at Corning, Inc. and other research labs throughout the world provide all students involved in the project with opportunities for interactions with industry and across national boundaries. This project focuses on employing (1) two-dimensional (2D) NMR methods that separate and correlate isotropic and anisotropic NMR frequencies arising from the Si-29 nuclear shielding and from O-17 nuclear electric quadrupole interactions, (2) 2D NMR methods that separate and correlate isotropic and Si-29 J couplings to determine quantitative distributions of NMR spectroscopic parameters present in glasses, and (3) inverse Laplace methods to determine the distribution of nuclear longitudinal and transverse relaxation times of Si-29 in multi-component silicate glasses, including alkali and alkaline-earth silicate and aluminosilicate glasses. The Grandinetti group is seeking quantitative distributions of specific structure quantities such as the distribution of network-forming anionic species (Qn), the Q3 silicon-non-bridging oxygen lengths, the inter-tetrahedral linkage angle and distances, intra-tetrahedral distortions, and cation percolation thresholds, by determining analytical relationships between NMR parameters and short- to medium-range structure. They also use the distribution of nuclear longitudinal and transverse relaxation times of Si-29 in multi-component silicate glasses to identify phase separation in glasses and gain insight into composition and structure of phase-separated regions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.