Magnetic relaxation in glass-bead/water dispersions

Abstract

Proton transverse magnetisation spin-echo decays have been recorded for glass-bead dispersions in water, acetone, chloroform and butan-1,4-diol as a function of measurement frequency and π pulse separation (t_cp). All the decays were non-exponential. With small beads (diameter < 60 µm), the characteristic decay time (T_2(eff)) was independent of frequency (15–60 MHz) and t_cp(0.1–4 ms) for water and butane-1, 4-diol, indicating that interactions with the surface provide the main T₂ mechanism. For acetone and chloroform similar results were obtained with t_cp < 1 ms. For longer pulse separations the values of T_2(eff) decreased as t_cp increased, with the rate of decrease being faster at higher measurement frequency. Here there is a contribution to T₂ from diffusion through field gradients arising from bulk susceptibility effects. The behaviour of dispersions containing larger beads (diameter ca. 140 µm) was similar, except that a contribution to the water T_2(eff) from bulk susceptibility effects was present with t_cp > 4 ms at 60 MHz.