NUCLEAR-RELAXATION IN IRREGULAR OR FRACTAL PORES

We apply a fractal description of pore surface irregularity to study t he nuclear relaxation of a liquid confined in an irregular pore. Our c alculation on a pre-fractal volume with infinite surface relaxation ra te shows that the long time relaxation behavior is dominated by an exp onential mode characterizing a free diffusive volume. At short time, t he calculated magnetization follows closely the power-law behavior pre viously proposed by de Gennes. For finite surface relaxation rate, we extend our studies of the efficiency of exchange on fractal membranes to nuclear relaxation in the same geometry. We predict a decay involvi ng two characteristic times. For very slow surface relaxation, there w ill exist exponential relaxation governed by the surface relaxation. T hese laws show that the pore surface irregularities may play an import ant role in nuclear relaxation.