A single-shot measurement of time-dependent diffusion over sub-millisecond timescales using static field gradient NMR

Code

• github.com/nathanwilliamson/SG-TIETA
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Abstract

Time-dependent diffusion behavior is probed over sub-millisecond timescales in a single shot using an NMR static gradient, time-incremented echo train acquisition (SG-TIETA) framework. The method extends the Carr-Purcell-Meiboom-Gill (CPMG) cycle under a static field gradient by discretely incrementing the -pulse spacings to simultaneously avoid off-resonance effects and probe a range of timescales (50 - 500 microseconds). Pulse spacings are optimized based on a derived ruleset. The remaining effects of pulse inaccuracy are examined and found to be consistent across pure liquids of different diffusivities: water, decane, and octanol-1. A pulse accuracy correction is developed. Instantaneous diffusivity, D_inst(t), curves (i.e., half of the time derivative of the mean-squared displacement in the gradient direction), are recovered from pulse accuracy-corrected SG-TIETA decays using a model-free, log-linear least squares inversion method validated by Monte Carlo simulations. A signal-averaged, 1-minute experiment is described. A flat D_inst(t) is measured on pure dodecamethylcyclohexasiloxane whereas decreasing D_inst(t) are measured on yeast suspensions, consistent with the expected short-time D_inst(t) behavior for confining microstructural barriers on the order of microns.

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