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  • 1
    Language: English
    In: The journal of physical chemistry. B, 27 February 2014, Vol.118(8), pp.2176-85
    Description: Here we investigate the organic ionic plastic crystal 1,2-bis[N-(N'-hexylimidazolium-d2(4,5))]ethane 2PF6(-) in one of its solid plastic crystal phases by means of multinuclear solid-state (SS) NMR and pulsed-field-gradient NMR diffusometry. We quantify distinct cation and anion diffusion coefficients as well as the Arrhenius diffusion activation energies (Ea) in this dicationic imidazolium-based plastic crystal. Our studies suggest a change in transport mechanism for the cation upon varying thermal and magnetic treatment (9.4 T), evidenced by differences in cation and anion Ea. Moreover, variable temperature (2)H SSNMR line shapes support a change in local molecular environment upon slow cooling in B0. We quantify the percentage of mobile anions as a function of temperature with (19)F SSNMR, wherein two distinct spectral features are present. We also comment on the Arrhenius pre-exponential factor for diffusion (D0), giving insight into the number of degrees of freedom for transport for both cation and anion as a function of thermal treatment. Given the breadth and depth of our measurements, we propose that bulk ion transport is dominated by anion diffusion in ionic-liquid-like domain boundaries separating crystallites. This study elucidates fundamental properties of this plastic crystal, and allows for a more general and deeper understanding of ion transport within such materials.
    Keywords: Anions ; Cations ; Plastics ; Diffusion ; Heat-Treatment ; Ionic-Crystals ; Bulk-Transport ; Ethane ; Crystallites ; Diffusion-Coefficient ; Transport-Mechanism ; Crystal-Phase ; Ionic-Liquid ; Anion ; Kation ; Kunststoff ; Diffusion ; Thermische Behandlung ; Ionenkristall ; Massenguttransport ; Ethan ; Kristallit ; Diffusionskoeffizient ; Transportmechanismus ; Kristallphase ; Ionische Flüssigkeit ; Chemistry;
    ISSN: 15206106
    E-ISSN: 1520-5207
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  • 2
    In: Chemical Communications, 2013, Vol.49(39), pp.4283-4285
    Description: We compare diffusion activation energy measurements in a hydrated perfluorosulfonate ionomer and aqueous solutions of triflic acid. These measurements provide insight into water transport dynamics on sub-nm length scales, and gauge the contribution of the polymer sidechain terminal group. Future membrane materials design will hinge on detailed understanding of transport dynamics.
    ISSN: 1359-7345
    E-ISSN: 1364-548X
    Source: Royal Society of Chemistry
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  • 3
    Language: English
    In: The journal of physical chemistry. B, 20 March 2014, Vol.118(11), pp.3207-17
    Description: Supramolecular assembly allows for enhanced control of bulk material properties through the fine modulation of intermolecular interactions. We present a comprehensive study of a cross-linkable amphiphilic wedge molecule based on a sulfonated trialkoxybenzene with a sodium counterion that forms liquid crystalline (LC) phases with ionic nanochannel structures. This compound exhibits drastic structural changes as a function of relative humidity (RH). Our combined structural, dynamical, and transport studies reveal deep and novel information on the coupling of water and wedge molecule transport to structural motifs, including the significant influence of domain boundaries within the material. Over a range of RH values, we employ (23)Na solid-state NMR on the counterions to complement detailed structural studies by grazing-incidence small-angle X-ray scattering. RH-dependent pulsed-field-gradient (PFG) NMR diffusion studies on both water and the wedge amphiphiles show multiple components, corresponding to species diffusing within LC domains as well as in the domain boundaries that compose 10% of the material. The rich transport and dynamical behaviors described here represent an important window into the world of supramolecular soft materials, carrying implications for optimization of these materials in many venues. Cubic phases present at high RH show fast transport of water (2 × 10(-10) m(2)/s), competitive with that observed in benchmark polymeric ion conductors. Understanding the self-assembly of these supramolecular building blocks shows promise for generating cross-linked membranes with fast ion conduction for applications such as next-generation batteries.
    Keywords: Strukturumwandlung ; Röntgenstrahl ; Diffusion ; Natrium ; Ionenkanal ; Relative Feuchtigkeit ; Dynamisches Verhalten ; Ionenleitung ; Baugruppe ; Selbstassemblierung ; Membran ; Chemistry;
    ISSN: 15206106
    E-ISSN: 1520-5207
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  • 4
    Language: English
    In: Chemical communications (Cambridge, England), 14 May 2013, Vol.49(39), pp.4283-5
    Description: We compare diffusion activation energy measurements in a hydrated perfluorosulfonate ionomer and aqueous solutions of triflic acid. These measurements provide insight into water transport dynamics on sub-nm length scales, and gauge the contribution of the polymer sidechain terminal group. Future membrane materials design will hinge on detailed understanding of transport dynamics.
    Keywords: Terminals ; Transport ; Hinges ; Diffusion ; Ionomers ; Aqueous Solutions ; Triflic Acid ; Dynamics ; Miscellaneous Sciences (So) ; Components and Materials (General) (Ea);
    ISSN: 13597345
    E-ISSN: 1364-548X
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  • 5
    Language: English
    In: Macromolecules, 07/25/2017, Vol.50(14), pp.5392-5401
    Description: We report a simple photo-cross-linking process to chemically arrest the different liquid-crystalline structures formed by self-assembly of wedge-shaped amphiphilic mesogens. Using this route, we obtained free-standing polymer membranes with columnar or bicontinuous cubic structures, depending primarily on the relative humidity conditions during UV-induced cross-linking. These cross-linked mesostructures show much higher thermal stability in comparison with that of the liquid-crystalline structures of the initial monomers. The ionic conductivity of the membranes strongly depends on the water uptake preceding the polymerization reaction. According to NMR diffusometry, which can quantify water transport in one or two environments in these materials, the water diffusion rate in the membrane with bicontinuous cubic structures can approach values of commercial ion conducting membranes. These studies show promise for use of this fabrication route in practical applications for selective ion and water transport.
    Keywords: Crystal-Structure ; Cubic-Structure ; Polymerisation-Reaction ; Ion-Transport ; Conducting-Polymers ; Diffusion-Rate ; Relative-Humidity ; Self-Assembly ; Ion-Conductivity ; Polymer-Membranes ; Monomers ; Absorption-Water ; Waterway-Transportation ; Kristalline Struktur ; Kubische Struktur ; Polymerisationsreaktion ; Ionentransport ; Leitendes Polymer ; Diffusionsgeschwindigkeit ; Relative Feuchtigkeit ; Selbstassemblierung ; Ionenleitfähigkeit ; Polymermembran ; Monomer ; Wasseraufnahme ; Wassertransport ; Chemistry;
    ISSN: 0024-9297
    E-ISSN: 1520-5835
    Source: American Chemical Society (via CrossRef)
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  • 6
    Language: English
    In: ChemInform, 11 October 2011, Vol.42(41), pp.no-no
    Description: Review: 194 refs.
    Keywords: Analytical Chemistry ; Review ; Magnetic Resonance ; Nuclear Quadrupole Resonance Organic Substances ; Magnetic Resonance ; Nuclear Quadrupole Resonance Solids And Liquids
    ISSN: 0931-7597
    ISSN: ChemInform
    E-ISSN: 1522-2667
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  • 7
    Language: English
    In: Radiology, November 2012, Vol.265(2), pp.418-25
    Description: To assess the feasibility of a perfusion magnetic resonance (MR) imaging technique that uses Overhauser dynamic nuclear polarization (DNP) to provide contrast during the continuous delivery of hyperpolarized water in rats. Protocols approved by the local institutional animal care and use committees were followed. Twelve male Wistar rats were anesthetized and prepared by placing injection tubing in the subcutaneous layer (n=3), peritoneum (n=3), aorta (n=3), or carotid artery (n=3). Water was hyperpolarized by means of Overhauser DNP in the 0.35-T fringe field of a 1.5-T MR imaging magnet by using a custom-built system to continuously deliver radical-free hyperpolarized water to the subject. Fast gradient-echo and spoiled gradient-recalled-echo MR imaging sequences were used. The signal-to-noise ratio (SNR) of the images was calculated and compared. Images showed greatly altered SNR and enhanced flow contrast at all injection locations. For subcutaneous and intraperitoneal injections, the water perfusion trajectory was observed for approximately 5 seconds after injection. Flow through a 4.2-cm length of artery was seen during intra-aortic injection. The right hemisphere of the brain was seen during injection into the right carotid artery. Images with hyperpolarized water had greatly altered SNR compared with images without injection or with the injection of nonhyperpolarized water, with a range of 13%-27% for the carotid and 444%-2900% for the other regions. Perfusion contrast for MR imaging can be obtained by continuously infusing hyperpolarized water, providing localized angiography or brain perfusion information in vivo for rat models.
    Keywords: Arteries -- Anatomy & Histology ; Contrast Media -- Chemistry ; Image Enhancement -- Methods ; Magnetic Resonance Angiography -- Methods ; Water -- Chemistry
    ISSN: 00338419
    E-ISSN: 1527-1315
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  • 8
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 06 February 2007, Vol.104(6), pp.1754-9
    Description: Pure water in a highly (1)H spin-polarized state is proposed as a contrast-agent-free contrast agent to visualize its macroscopic evolution in aqueous media by MRI. Remotely enhanced liquids for image contrast (RELIC) utilizes a (1)H signal of water that is enhanced outside the sample in continuous-flow mode and immediately delivered to the sample to obtain maximum contrast between entering and bulk fluids. Hyperpolarization suggests an ideal contrast mechanism to highlight the ubiquitous and specific function of water in physiology, biology, and materials because the physiological, chemical, and macroscopic function of water is not altered by the degree of magnetization. We present an approach that is capable of instantaneously enhancing the (1)H MRI signal by up to 2 orders of magnitude through the Overhauser effect under ambient conditions at 0.35 tesla by using highly spin-polarized unpaired electrons that are covalently immobilized onto a porous, water-saturated gel matrix. The continuous polarization of radical-free flowing water allowed us to distinctively visualize vortices in model reactors and dispersion patterns through porous media. A (1)H signal enhancement of water by a factor of -10 and -100 provides for an observation time of 〉4 and 7 s, respectively, upon its injection into fluids with a T(1) relaxation time of 〉1.5 s. The implications for chemical engineering or biomedical applications of using hyperpolarized solvents or physiological fluids to visualize mass transport and perfusion with high and authentic MRI contrast originating from water itself, and not from foreign contrast agents, are immediate.
    Keywords: Contrast Media ; Magnetic Resonance Imaging ; Water
    ISSN: 0027-8424
    E-ISSN: 10916490
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  • 9
    Language: English
    In: Macromolecules, 15 October 2015, Vol.46((19) ; 10, 2013)
    Description: Abstract not provided. Journal Article.
    Keywords: Chemistry
    ISSN: 0024-9297
    E-ISSN: 1520-5835
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  • 10
    Language: English
    In: Journal of Magnetic Resonance, 2010, Vol.204(1), pp.56-63
    Description: Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) at very low magnetic fields (0.05–20 mT) have gained interest due to the simple and portable magnet design and newly emerging applications outside of the usual laboratory setting. A method to enhance the NMR signal is needed due to the low thermal polarization of nuclear spins at these fields; dynamic nuclear polarization (DNP) via the Overhauser effect from free radicals is an attractive option. In this report we describe a DNP-enhanced NMR system operating at a fixed field of 1.5 mT and measure H signal enhancements of up to −350 fold during the saturation of a selected electron spin resonance (ESR) transition of dissolved nitroxide radicals. This −350 fold enhanced polarization is equivalent to what would be obtained by prepolarization in a 0.53 T field. The ESR spectra at varying radical concentrations are indirectly found through DNP-enhanced NMR detection. Here, ESR line broadening at higher radical concentrations due to Heisenberg electron spin exchange is observed. Enhancements in the limit of maximum power are reported as a function of concentration for three ESR transitions, and are found to increase with concentration. The 〉300 fold H NMR signal amplifications achievable at 1.5 mT will reduce experimental time by several orders of magnitude, permitting NMR relaxation, imaging or pulsed-field gradient diffusion experiments that are inaccessible without using the DNP effect at 1.5 mT. We demonstrate the potential benefit of such large signal amplification schemes through and relaxation measurements carried out in a much shorter time when employing DNP. Finally, we compare our results to those obtained in the earth’s magnetic field and find that the signal to noise ratio (SNR) of DNP-enhanced signal at 1.5 mT is much greater than that obtained by previous studies utilizing DNP enhancement in the 0.05 mT earth’s magnetic field.
    Keywords: Dynamic Nuclear Polarization ; Dnp ; Hyperpolarization ; Overhauser Effect ; Low Field ; NMR ; Portable NMR ; Portable Mri ; Chemistry ; Physics
    ISSN: 1090-7807
    E-ISSN: 1096-0856
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