Fast Field Cycling NMR Relaxometry Research Articles

From Simple Liquid to Polymer Melt. Glassy and Polymer Dynamics Studied by Fast Field Cycling NMR Relaxometry: Rouse Regime

We apply fast field cycling NMR to study the dispersion of the 1H spin−lattice relaxation time T1(ω) of linear 1,4-polybutadienes with molecular weight M (g/mol) ranging from M = 355 to 817 000. By...

From Simple Liquid to Polymer Melt. Glassy and Polymer Dynamics Studied by Fast Field Cycling NMR Relaxometry: Low and High Molecular Weight Limit

Fast field cycling (FFC) NMR is applied to study the dispersion of the 1H spin−lattice relaxation in the low molecular weight glass-formers o-terphenyl, tristyrene, and oligomeric polybutadiene (PB, with M/gmol−1 = 355 and 466) over a broad temperature range (203−401 K). Differing from previous FFC NMR works, we analyze the relaxation data in the susceptibility form ω/T1(ω), and applying frequency−temperature superposition, master spectra are obtained covering up to 8 decades in frequency. In all cases solely the glassy dynamics (α-process) determines the relaxation behavior, and the Rouse unit is estimated to MR ≅ 500 g/mol. The time constant τα(T) in the range 10−11−10−6 s is extracted, which agrees well with those measured at the same time by dielectric spectroscopy. For the high molecular weight PB (M/gmol−1 = 56 500, 87 000, 314 000, and 817 000) pronounced polymer effects are observed at low frequencies (ωτα ≪ 1) which are isolated from the total spectrum by subtracting the “glass spectrum” as obtai...

Design and Test of a Compound Persistent-Pulsed Magnet for Fast Field Cycling NMR

In order to investigate the possibility of using superconducting magnets for fast field cycling (FFC) NMR relaxometry, a NbTi magnet able to achieve high field variation rates in a constant background field has been designed and tested. The design layout consists in an outer superconducting magnet working in persistent mode and an inner superconducting magnet working in pulsed mode. The layout of the inner magnet has been optimized taking into account field strength, field homogeneity, stray field and inductive coupling with outer magnet. A demonstration pulsed magnet has been tested in a background field, achieving the main desired working features.

NMR study of the slow dynamics and local structure in lyotropic micellar liquid crystals

The first experimental evidence of director fluctuations in a micellar lyotropic liquid crystal, studied by 1H spin-lattice relaxation rate, is reported. The system is constituted by the ternary mixture: potassium laurate/1-decanol/water. With the aim to test the slow dynamics, the experiment has been performed over a broad range of Larmor frequencies (2 × 103− 6.6 × 106 Hz), using fast field-cycling NMR relaxometry. The results evidence that in the nematic and isotropic mesophases and the poliphasyc region, director fluctuations are responsible for the spin-lattice relaxation dispersion in the low Larmor frequency range ( 105 Hz), two relaxation mechanisms are assigned: i) molecular reorientation by translational diffusion on the micellar surface, and ii) molecular exchange between the micelle and the bulk.