Measuring Bond Angle Distributions in Silicate Glasses with 2D J PIETA NMR
Keywords:NMR physical chemistry
MetadataShow full item record
Series/Report no.:2016 Richard J. and Martha D. Denman Undergraduate Research Forum. 21st
The importance of measuring the distribution of Si-O-Si angles in silicate glasses cannot be overstated. It is the first broken structural constraint and the variation in these angles is considered to be one of the main sources of disorder in silicate glasses. The 2JSi-O-Si coupling in nuclear magnetic resonance (NMR) spectroscopy can be used as a probe of structure in the Si-O-Si linkage, although the size of this coupling in silicates is on the order of 0 to 15 Hz. The greatest utility of the 2JSi-O-Si coupling, to date, has been in establishing through-bond connectivities between Q(n) units, forming the basis of a number of successful INADEQUATE NMR studies in silicates, as well as analogous 31P NMR studies exploiting the 2JP-O-P coupling in phosphate glasses. We recently developed the Phase Incremented Echo Train Acquisition (PIETA) method for more accurate measurement of transverse relaxation behavior and J coupling evolution during echo train acquisition. In this three-dimensional experiment we separate and correlate the 29Si chemical shift to the 29Si-29Si J coupling spectrum to the 29Si T2 relaxation "spectrum". Our results on silica glass show a Si-O-Si bond angle distribution that is similar to previous 17O DAS NMR results with a distribution peak at 147◦ and extending over a range of angles from 140◦ to 154◦. We will also present results on mesoporous silica with 4 nm ordered pores. Here the bond angle distribution peaks at 146◦ and extending over a range of angles from 140◦ to 153◦. Interestingly, we observe little variation in the distribution of 2JSi-O-Si couplings for the Q(3) site, consistent with the Q(3) residing on the walls of the ordered pores.
Mathematical and Physical Sciences: 3rd Place (The Ohio State University Denman Undergraduate Research Forum)
Academic Major: Chemistry
National Science Foundation
Items in Knowledge Bank are protected by copyright, with all rights reserved, unless otherwise indicated.