The resin-asphaltene model systems with different sizes of asphaltenes are studied by nuclear magnetic resonance (NMR) using the solid-echo sequence. For systems with particle sizes of asphaltenes greater than 50 µm, the form of relaxation attenuation consists of two components, one of which is characterized by a typical asphaltene relaxation time of about 20 µs. In this case, the Gaussian form describes the relaxation attenuation of this component, which is typical for the NMR signal in disordered solids. At the same time, it is found that the share of the solid component in the NMR signal decreases with decreasing particle size of asphaltenes. The signal drops to zero when the size of asphaltenes particles reaches 10 microns. Based on the estimates of the rotational motion correlation time for an asphaltene particle in a dispersion medium (resin) with a known viscosity value, the influence of two factors is discussed: the difference in the values of macro- and microviscosity of the resin, as well as the possibility of partial dissolution of asphaltenes particles in the resin. The results of repeated measurements for a long time indicate the existence of a reverse process in the system, leading to the aggregation of asphaltene particles.

The resin-asphaltene model samples are studied by nuclear magnetic resonance (NMR). According to the differences in spin-spin relaxation times, we are able to distinguish two components of the resin in the mixture. The first component with slower relaxation rate corresponds to the resin in bulk. The second component with the much higher relaxation rate conforms to the resin interacting with the asphaltene particles. The dependence of the ratio between the contributions of these functions on the particle size of asphaltenes is found. It is shown that the fraction of resin molecules interacting with asphaltenes is described by the power dependence on the particle size in terms of one particle. In this case, the proportionality to the volume is given by the value of the exponent (0.9) that is closer to unity, while this exponent is 1.33 for the particle surface. This result is not consistent with the conventional simple model of an asphalt particle surrounded by a solvate resin layer. A hypothesis is formulated about the partial dissolution of asphaltene molecules in the resin is formulated, which is also confirmed by the dependence in the NMR signal of the fraction of the solid component on the particle size of asphaltenes. It is shown that the kinetic dependences of the fraction of the solid component, as well as the fraction of the resin molecules in the state of interaction with asphaltenes, reflect in general the opposite processes, although they are characterized by a close time value of 20 days.

Pulsed nuclear magnetic resonance (NMR) spectrometer operating in weak magnetic field (~100 Oe) with the dynamic nuclear polarization (DNP) is described. The spectrometer is designed to study the Overhauser DNP effect in natural hydrocarbons for potential using DNP techniques to enhance the ¹H NMR signal in crude oil and petroleum products. The unit was tested on a sample of the ethylene glycol chromium complex at room temperature. A DNP enhancement of ε = −50 for ¹H NMR signal from solvent protons by pumping ⁵²Cr⁵⁺ electronic transitions with the optimized pumping parameters was achieved.

We report the electronic paramagnetic resonance (EPR) studies on single crystals of LiRF₄ (R = Y and Lu) doped with Er³⁺ ions in the frequency range of 37-1040 GHz at the liquid helium temperature. Resonance transitions between the Zeeman sublevels of three lower crystal field Kramers doublets of Er³⁺ ions in magnetic fields up to 1 Tesla are registered. A prominent anisotropy of the EPR spectra in magnetic fields lying in the ab plane of the tetragonal crystal lattice is revealed. The revised set of free-ion and crystal field parameters for LiYF₄:Er³⁺ and the new one for LiLuF₄:Er³⁺ allow us to reproduce successfully the measured frequency and angular dependences of the resonant magnetic fields.

The detailed ab initio calculations of crystal structure and hyperfine interaction parameters are presented for R₂V₂O₇ system (R = Ho, Er, Tm, Yb, Lu) to investigate the effect of the V-ion environment due to R-ion substitution on the local magnetic properties of ⁵¹V nucleus. It is shown that this effect is very small, but the orbital ordering dictates a large anisotropy of magnetic hyperfine tensor in R₂V₂O₇ system.