THEORY OF NUCLEAR-SPIN RELAXATION IN HETEROGENEOUS MEDIA AND APPLICATION TO THE CROSS-CORRELATION BETWEEN QUADRUPOLAR AND DIPOLAR FLUCTUATIONS OF DEUTERONS IN CLAY GELS

The fictitious-spin- 1 2 operator formalism allows a comprehensive study of the longitudinal and transverse nuclear relaxations of a nuclear spin I = 1 in heterogeneous media, in the presence of a residual time-averaged quadrupolar interaction. An extension of this formalism makes possible the calculation of the cross correlation between the quadrupolar and dipolar (paramagnetic) fluctuations. Although this cross correlation is second order relative to the quadrupolar relaxation, its long range of effectiveness (∞ 1 r3) is sufficient to provide the sole asymmetric component to the fine broadening of the deuterium doublet. This differential line broadening depends linearly on the applied magnetic induction field and on the paramagnetic spin concentration, as checked experimentally from a lineshape analysis of the 2H doublet observed for D20 in clay gels. The reorientational correlation time of the adsorbed water at the clay interface is obtained from the measured 2H spin-relaxation rates. © 1992.