Characterization of micro-domain structure of solvent-swollen coal by small angle neutron scattering and proton spin diffusion

Blind Canyon coal was swollen by deuterated pyridine and was subjected to small angle neutron scattering (SANS) and ¹H NMR relaxation measurements. Based on the transverse relaxation characteristics, it was found that there exist at least two distinct structural regions in the swollen coals. However the measured longitudinal relaxation was best characterized by a single component as spin diffusion is rapid in the swollen coals. The dynamics of spin diffusion were revealed using a partially modified Goldman-Shen pulse sequence and analyzed by a simple mathematical model of a two phase system. The interdomain spacing, d_i, was estimated based on the diffusive path length for each spatial dimension. The d_i value evaluated under one-dimension was 15 nm and agreed with d_i determined by SANS, suggesting that the domain shape is sheet.