[en] We present a study of the molecular dynamics in an octylcyanobiphenyl (8CB)-Aerosil complex above the bulk isotropization temperature. Using proton nuclear magnetic relaxation experiments in the laboratory frame (T₁^-1) and in the rotating-frame (T_1ρ^-1), we found a notable increase of the relaxation rates in the kHz frequency range as compared to the bulk 8CB liquid crystal at the same temperature. The field-cycling technique was used for the laboratory frame experiments while a conventional apparatus was used for the rotating frame method. The observed behavior is analyzed with the aid of Monte Carlo simulations on the basis of a two-phase fast-exchange model distinguishing surface-ordered and bulk phases. Two processes affecting the low frequency relaxation could be identified: reorientation mediated by translational displacements, accounting for molecular reorientations, and exchange losses of molecules from the surface to the bulk

[en] Short communication

[en] Published in summary form only

No abstract available

No abstract available

[en] We present advances on the study of a nuclear magnetic resonance technique in the rotating frame. The method, based on the spin-lock experiment, allows to get information on the residual local fields in molecular organized materials. The magnetization after a certain lock-time is studied as a function of the radio-frequency field attenuation. The obtained dispersion curve, within a frequency interval ranging from a few k Hz to about 50 k Hz, contains information about the residual local field along the external magnetic field. The interpretation of the results is consistent and comparable with those obtained by other methods. (Author)

[en] The present work was undertaken in order to investigate lubricant oil degradation at the molecular level. Ageing effects, as reflected on the proton spin-lattice relaxation rate (T₁¹) dispersion, were studied in two different lubricant engine oils. The proton field cycling technique was used to scan relaxation of new and aged samples of monograde and multigrade oils. Relaxation dispersions were interpreted in terms of self-diffusion and molecular rotations. Our study shows that proton T₁¹ could be very sensitive to degradation processes, especially at low Larmor frequencies. The analysis reveals a noticeable sensitivity of the involved correlation times. The pros and cons of the technique are also discussed

No abstract available

[en] In this manuscript we describe an -helical-cut notch-coil magnet system designed for fast switching of the magnetic field. An attempt was made to determine the extent to which such a magnet configuration can be efficiently used for fast-field-cycling (FFC) nuclear magnetic resonance (NMR) instruments. In addition to the typical technical requirements (high field-to-power ratio, adequate electric performance for fast-switching of the magnetic field and NMR-compatible magnetic field homogeneity), a tunable homogeneity within the sample volume and more uniform heat dissipation along the magnet body are included. A helical-cut notch-coil machined in metallic cylinders with external movable pieces was found to fit these requirements very well. A key factor for the optimization of the magnet parameters is the use of a novel calculation procedure based on a more realistic model that consider a magnet geometry with broken azimuthal symmetry. The aim of this paper is to theoretically compare the proposed geometry with other existing designs. No particular prototype is presented here. A clear understanding of the notch-coil performance was found to be an essential step for its further consideration as a potential autoadaptive (electronically controlled) magnet system for FFC applications. (author)