title: Mesoscale spatial distribution of electron spins studied by time-resolved small-angle and ultrasmall-angle neutron scattering with dynamic nuclear polarization: a case of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) doped in high-density polyethylene.
abstract: We carried out time-resolved small-angle neutron scattering (SANS) and ultrasmall-angle neutron scattering (USANS) studies of dynamically polarized high-density polyethylene (HDPE) doped with 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) persistent free radicals. We observed a remarkable enhancement of the scattering intensity shortly after a switching of microwave frequency from positive (negative) to negative (positive) dynamic nuclear polarization (DNP). The enhancement was found to be due to spatially heterogeneous proton-spin polarization generated as a result of heterogeneously distributed TEMPO in the HDPE sample. The spatial fluctuation of the polarization ranged up to the length-scale of > or = 100 nm. This result strongly suggests that the TEMPO free radicals are localized more in nonfibrils but less in fibrils of HDPE. In this way, we propose that the time-resolved DNP-SANS and DNP-USANS be general techniques to determine mesoscale spatial distribution of electron spins in dielectric materials.
authors: Quantum Beam Science Directorate, Kansai Photon Science Institute, Japan Atomic Energy Agency, Umemidai, Kizugawa, Kyoto 619-0215, Japan. kumada.takayuki@jaea.go.jp
authors: Takayuki
authors: T
authors: Kumada
authors: Yohei
authors: Y
authors: Noda
authors: Satoshi
authors: S
authors: Koizumi
authors: Takeji
authors: T
authors: Hashimoto
mesh_terms: D003497:Cyclic N-Oxides / Q000737:chemistry*; D004583:Electrons; D005609:Free Radicals / Q000737:chemistry; D020959:Polyethylene / Q000737:chemistry*; D053838:Scattering, Small Angle; D013997:Time Factors; D014961:X-Ray Diffraction
chemical_list: D003497:Cyclic N-Oxides; D005609:Free Radicals; D020959:Polyethylene; C003959:TEMPO