Applications of DNP enhanced 1H-1H spin diffusion analyses for measurement of domain sizes in hydrated inorganic solids

Nathan Prisco
Nathan Prisco
Engineering II - 1519

Conventionally, solid-state NMR is limited to resolving local electronic environments (up to ~1.2 nm) of nuclear spin ensembles. When spin polarization is transferred from electron spins in stable nitroxide biradicals to proximate nuclear spins, enhanced levels of nuclear spin polarization may be relayed from distances ranging from <1 nm to 10’s µm depending on the relative rates of spin polarization generation and relaxation in the media. Dynamic Nuclear Polarization surface-enhanced NMR spectroscopy (DNP-SENS) has shown great promise in its ability to resolve spatial and chemical gradients in ordered or disordered materials. These analyses require the use of a quantum mechanical, lattice, or continuum-scale model to understand the underlying polarization transfer dynamics. Here, a DNP film coefficient (kDNP) is introduced to describe the rate of polarization exchange between electron and nuclear spins; and kDNP values are extracted from experimental polarization build-up curves measured for AMUPol glycerol/water solutions. From which, numerical and analytical solutions of heat transfer models predict a wide-range of polarization transfer phenonema that may be observed in MAS-DNP experiments. By application of 1H-1H spin diffusion models, experimental polarization build-up t imes (TB), stretched-exponential factors (β), and DNP enhancements ( ) may be used to estimate characteristic dimensions (e.g., surface-layer thicknesses or domain sizes) over challenging length scales (<1 nm – 100’s nm).