ULTRASMALL-ANGLE AND SMALL-ANGLE X-RAY-SCATTERING OF SMECTITE CLAY SUSPENSIONS

Incomplete swelling of clay leads to diphasic samples characterised by a broad Bragg peak produced by crystallites of a limited size of less than ten parallel clay platelets. The excess water gives rise to an i ntense small-angle scattering produced by polydisperse water inclusion between the crystallites. Ultrasmall-angle X-ray scattering (USAXS) m easurement of the power-law decay of this scattering is described usin g two model systems: laponite and montmorillonite in pure water and wi th added salt. With added salt, the compactness of the clay network de pends on the sample preparation procedure.