Light-Scattering Study of Bentonite Solutions when Subjected to Electric Fields

Abstract

A brief account of the theory is given, and the results presented for a light‐scattering study of Wyoming sodium bentonite solutions in the absence and presence of applied electric fields. Measurements made without electric fields gave no indication of the side‐by‐side aggregates found by other workers. If it is assumed that the particles are flat disks, the data indicates a radius of 3400 Å, and a thickness of 9.4 Å. The application of alternating current fields to solutions of polar or electrically anisotropic particles results in a change in the angular scattering pattern, and moreover enables a distinction to be made between these two classes. Furthermore such fields introduce an alternating scattered intensity component of twice the frequency of the applied field. The solutions were subjected to fields up to 374 V cm⁻¹ at frequencies up to 400 cps and were found to consist of at least two kinds of particles. Consideration of the frequency dependence of the intensity changes enabled rotary diffusion constants to be estimated, which in turn indicated the relative particle sizes of the two constituents. Measurements of the alternating intensity changes supported the results obtained from the data with the nonalternating changes, and this confirms the usefulness of detecting and measuring these components. x‐ray diffraction studies have revealed the two constituents of the bentonite to be sodium montmorillonite, gypsum, and quartz.