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Träfflista för sökning "WFRF:(Magusin Pieter C.M.M.) "

Sökning: WFRF:(Magusin Pieter C.M.M.)

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1.
  • Fitie, Carel F. C., et al. (författare)
  • Polar Switching in Trialkylbenzene-1,3,5-tricarboxamides
  • 2012
  • Ingår i: Journal of Physical Chemistry B. - : American Chemical Society. - 1520-6106 .- 1520-5207. ; 116:13, s. 3928-3937
  • Tidskriftsartikel (refereegranskat)abstract
    • The hydrogen-bonded hexagonal columnar LC (Col(hd)) phases formed by benzene-1,3,5-tricarboxamide (BTA) derivatives can be aligned uniformly by an electric field and display switching behavior with a high remnant polarization. The polar switching in three symmetrically substituted BTAs with alkyl chains varying in length between 6 and 18 carbon atoms (C6, C10, and C18) was investigated by electro-optical switching experiments, dielectric relaxation spectroscopy (DRS), and solid-state NMR The goal was to characterize ferroelectric properties of BTA-based columnar LCs, which display a macroscopic axial dipole moment due to the head-to-tail stacking of hydrogen-bonded amides. The Col(hd) phase of all three BTAs can be aligned uniformly by a dc field similar to 30 V/mu m. Moreover, C10 and C18 display extrinsic polar switching characterized by a remnant polarization and coercive field of 1-2 mu C/cm(2) and 20-30 V/mu m, respectively. In the absence of an external field, the polarization is lost in 1-1000 s, depending on device details and temperature. DRS revealed a columnar glass transition in the low-temperature region of the LC phase related to collective vibrations in the hydrogen-bonded columns that freeze out below 41-54 degrees C. At higher temperatures, a relaxation process is present originating from the collective reorientation of amide groups along the column axis (inversion of the macrodipole). Matching activation energies suggest that the molecular mechanism underlying the polar switching and the R-processes is identical. These results illustrate that LC phases based on BTAs offer the unique possibility to integrate polarization with other functionalities in a single nanostructured material.
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2.
  • Jin, Yanting, et al. (författare)
  • Understanding Fluoroethylene Carbonate and Vinylene Carbonate Based Electrolytes for Si Anodes in Lithium Ion Batteries with NMR Spectroscopy
  • 2018
  • Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 140:31, s. 9854-9867
  • Tidskriftsartikel (refereegranskat)abstract
    • Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are widely used as electrolyte additives in lithium ion batteries. Here we analyze the solid electrolyte interphase (SEI) formed on binder-free silicon nanowire (SiNW) electrodes in pure FEC or VC electrolytes containing 1 M LiPF6by solid-state NMR with and without dynamic nuclear polarization (DNP) enhancement. We find that the polymeric SEIs formed in pure FEC or VC electrolytes consist mainly of cross-linked poly(ethylene oxide) (PEO) and aliphatic chain functionalities along with additional carbonate and carboxylate species. The formation of branched fragments is further confirmed by13C-13C correlation NMR experiments. The presence of cross-linked PEO-type polymers in FEC and VC correlates with good capacity retention and high Coulombic efficiencies of the SiNWs. Using29Si DNP NMR, we are able to probe the interfacial region between SEI and the Si surface for the first time with NMR spectroscopy. Organosiloxanes form upon cycling, confirming that some of the organic SEI is covalently bonded to the Si surface. We suggest that both the polymeric structure of the SEI and the nature of its adhesion to the redox-active materials are important for electrochemical performance.
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