Introduction

The Sandia National Laboratories NMR Spectroscopy Facility maintains both high resolution solution and solid state capabilities for the characterization of chemical structure, reaction kinetics, morphologies and dynamic properties for a wide range of materials. Our research includes the development and implementation of both multi-frequency and multi-dimensional NMR experiments to probe specific chemical or materials science related questions.

New and Notable: HRMAS NMR Spectroscopy in Material Science

Recently Published: Computing the ⁷Li NMR Chemical Shielding of Hydrated Li⁺ Using Cluster Calculations and Time-Averaged Configurations from Ab Initio Molecular Dynamics Simulations

Research Interests

Structure and Dynamics in Ionomers

Precise manipulation of structure within ionomer membranes continues to be an area of interest. In collaboration with University of Pennsylvania a series of poly(ethylene-co-acrylic acid) copolymers P(E-AA) have been prepared to address the role of carboxylic acid spacing.Utilizing samples with precise versus random placement of the pendant carboxylic acid group, the effect on structure, morphology, and dynamics is being investigated. Solid state ¹H and ¹³C MAS NMR spectroscopy is being used to characterize these changes. The NMR reveals that the changes in the P(E-AA) structure and dynamics imposed by these carboxylic acid defects are distinct, and vary with temperature and the degree of Zn²⁺, Li⁺ or Na⁺ neutralization. These results are being combined with ab initio calculations of NMR shielding parameters to understand the experimental results.

Figure 1: 2D 1H MAS NMR correlation experiments in P(E-AA) ionomers: a) DQ BaBa and b) NOESY.

For more information, contact Todd M. Alam.

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Structure and Dynamics in Inorganic Systems

Both solution and solid-state NMR has been use to look at a range of inorganic materials. Recently we have employed solid state ^6,7Li MAS NMR and wide line ¹³⁹La NMR to probe the impact of processing on Li-La-Nb/Ta Garnet electrolytes and lanthanum halides. High speed ¹H MAS NMR has also been employed to look at the role of templating in ruthenium oxide electrodes. The dynamics in Uranyl Nanocapsules utilizing 23Na solution and solid state has also been descriped in JACS:

For more information, contact Todd M. Alam.

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Dynamics in Ionic Liquids

With the increasing interest in room temperature ionic liquids (ILs) for a variety of application our recent research has focused on the use of NMR to probe the local dynamics and transport properties in these materials. We recently demonstrated in collaboration with UT Austin that ¹⁴N NMR provides the perfect tool to determine reorientational correlation times in quaternary ammonium ILs and cyclic pyrrolidinium ILs. The diffusion properties of these ionic liquids have also been measured by using pulse field gradient (PFG) NMR techniques. We have also begun efforts to combine ab initio calculations of ILs to the observed NMR parameters.

Figure 3:  14N NMR relaxation experiments for the direct determination of molecular correlation times.

For more information, contact Todd M. Alam.

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Theoretical Calculations of CWA/Water/Interfaces

Sarin work can be found in: COMPUTATONAL & THEORETICAL CHEMSTRY - SPECIAL ISSUE

This research is aimed at developing a molecular level understanding into the role water, including dissolved electrolytes plays on the interaction, lifetime and reaction kinetics of chemical warfare agents (CWA), particularly nerve agents or organophosphate agents (OPA), on inorganic surfaces. The importance of water, including dissolved electrolytes, on CWA-surface interactions remains unclear and is the driving force of this effort. Combined molecular dynamics (MD) simulations and ab initio quantum calculations are being used to understanding and predicting these water-CWA-surface interactions. Current efforts include understanding the micro-hydration of CWA, and the impact of water adsorption on the interaction of CWA with silica surfaces.

Figure 4: a) Dimethyl methylphosphonate (DMMP), a simulant used for Sarin, adsorbed to an amorphous silica surface. Adsorption was calculated using the ONIOM method, ONIOM (b3lyp/6-311++g(2d,2p):UFF), with the ball and stick representing "High" theory and the wireframe representing "Low." b) Sarin adsorbed to H3SiOH in the presence of three explicit waters. Adsorption calculated using b3lyp/6-311++g(2d,2p).

For more information, contact Todd M. Alam