Interpretation of small-angle x-ray scattering data from dilute montmorillonite suspensions using a modified Guinier approximation - art. no. 021401

Smectites are a group of 2:1-layer phyllosilicate minerals that have been e xtensively studied by small-angle x-ray scattering (SAXS) because of their industrial and environmental significance. In previous studies, a Guinier p lot has been used to obtain the radius of gyration of the clay particles, f rom which geometric information of the particle structure is derived. Using an indirect Fourier transform to treat SAXS data from a dilute montmorillo nite suspension, a negative electron contrast at the clay-water interface i s observed. This electron inhomogeneity has violated the assumption underly ing the application of the Guinier plot, which requires particles to have a uniform electron density. The presence of this inhomogeneity explains the inability of previous studies to correctly determine particle dimensions us ing the Guinier plot. Using this model of the clay-water interface, a modif ied Guinier plot has been derived and was experimentally verified. The calc ulation shows the presence of negative electron contrast at montmorillonite -water interfaces, which is in accordance with the results from the indirec t Fourier transform method. This approximation has the potential to predict the geometric information for similar colloids studied by small-angle scat tering.