title: Interpretation of small-angle x-ray scattering data from dilute montmorillonite suspensions using a modified Guinier approximation.
abstract: Smectites are a group of 2:1-layer phyllosilicate minerals that have been extensively studied by small-angle x-ray scattering (SAXS) because of their industrial and environmental significance. In previous studies, a Guinier plot has been used to obtain the radius of gyration of the clay particles, from which geometric information of the particle structure is derived. Using an indirect Fourier transform to treat SAXS data from a dilute montmorillonite suspension, a negative electron contrast at the clay-water interface is observed. This electron inhomogeneity has violated the assumption underlying 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 using the Guinier plot. Using this model of the clay-water interface, a modified Guinier plot has been derived and was experimentally verified. The calculation shows the presence of negative electron contrast at montmorillonite-water interfaces, which is in accordance with the results from the indirect Fourier transform method. This approximation has the potential to predict the geometric information for similar colloids studied by small-angle scattering.
authors.affiliation: Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota 57007-0896, USA.
authors.forename: C
authors.initials: C
authors.lastname: Shang
authors.forename: J A
authors.initials: JA
authors.lastname: Rice