NMR methodologies for measuring correlated structural distributions in oxide glasses

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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.