| 1. |
- Dvinskikh, Sergey V., et al.
(author)
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C-13 PGSE NMR experiment with heteronuclear dipolar decoupling to measure diffusion in liquid crystals and solids
- 2000
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In: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 142:1, s. 102-110
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Journal article (peer-reviewed)abstract
- A new PGSE NMR experiment, designed to measure molecular diffusion coefficients in systems with nonvanishing static dipolar coupling, is described. The fast static dipolar dephasing of the single-quantum C-13 coherences is removed by multiple-pulse heteronuclear decoupling. The resulting slow dephasing of the C-13 coherences allows for inserting appropriate gradient pulses into the pulse sequence. The presence of the large magnetic field gradient reduces the efficiency of the decoupling sequences which is compensated for by introducing a scheme of sequential slice selection across the sample. The method is demonstrated by F-19-decoupled C-13 PGSE NMR experiments in a lyotropic nematic and lamellar liquid crystal,
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| 2. |
- Sitnikov, R., et al.
(author)
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Nuclear magnetic resonance spectrometer with a frequency range extended below the megahertz region
- 2000
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In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 71:2, s. 450-457
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Journal article (peer-reviewed)abstract
- A conventional nuclear magnetic resonance (NMR) spectrometer with an original low-frequency limit of 2 MHz and equipped with an electromagnet is rebuilt to allow performing NMR experiments at resonance frequencies down to 100 kHz. The instrument is intended for accurate field-dependent spin relaxation studies. The preamplifier and the duplexer are completely replaced by new designs that provide low noise figure, large gain and fast recovery. The receiver, the transmitter, and the magnet power supply are modified to operate at low frequency (receiver and transmitter) and at low current (power supply). The performance of the instrument is demonstrated by H-2 NMR experiments in the 500 kHz-2 MHz region and is compared to that of instruments based on direct current-superconducting quantum interference device and operated on room-temperature samples.
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| 3. |
- Tornblom, M., et al.
(author)
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A H-2 NMR study of order and dynamics in the cubic I-1 phase of the dodecyltrimethylammonium chloride/water system
- 2000
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In: Liquid crystals (Print). - 0267-8292 .- 1366-5855. ; 27:7, s. 943-955
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Journal article (peer-reviewed)abstract
- The micellar cubic phase I-1 of the dodecyltrimethylammonium chloride (C(12)TACl)/water system has been studied by H-2 NMR spectroscopy. Relaxation rates of selectively deuteriated surfactant were measured at several frequencies down to 0.5 MHz in the temperature range 25-61 degrees C. The results are interpreted within models for the reorientational dynamics in I, phases and it is concluded that the remaining order after surface diffusion and aggregate rotation is small and does not vary substantially with temperature. The results are discussed in relation to the two prevailing models for the structure of these phases as suggested (separately) by Fontell and Vargas. At 0 degrees C the 2H NMR Spectrum from perdeuteriated n-dodecane solubilized in this phase shows static quadrupole splittings with a magnitude that is in good agreement with the results obtained from the analysis of the relaxation data.
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| 4. |
- Tornblom, M., et al.
(author)
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Field-dependent NMR relaxation study of aggregation and dynamics in dilute to concentrated micellar decylammonium chloride solutions
- 2000
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 104:7, s. 1529-1538
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Journal article (peer-reviewed)abstract
- The surfactant aggregation behavior in aqueous decylammonium chloride solutions for concentrations between 5 and 29 wt % was studied by H-2 nuclear magnetic relaxation dispersion in the 0.5-77-MHz frequency range. Below the second cmc the micelles can be described as polydisperse fairly small aggregates undergoing unhindered Brownian rotation. Above the second cme the micelles are rod shaped and grow with increasing concentration, and as a consequence the tumbling of the micelles eventually becomes restricted by neighboring aggregates, which is demonstrated by the low-frequency relaxation data. The restricted reorientation of the micelles in the concentrated solution has been modeled as rotational diffusion in a hard-walled double cone potential of mean torque.
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