Surface modification of clay minerals by organic polyions

Parallel studies were made of the solid/gas and solid/liquid interfacial properties and the colloidal behaviour of aqueous dispersions of two types of material: soil mineral grains which had been coated with natural organic matter (humus) and clay minerals (montmorillonite and kaolinite) whose surfaces had been modified synthetically with an organic polyacid, as models for organo-mineral complexes. Solid samples with and without a polyionic organic coating, and also their aqueous suspensions, were investigated by means of nitrogen gas adsorption, small-angle X-ray scattering, potentiometric acid-base titration and rheological methods. The organic coating was found to exist as a rough layer on the surface of the mineral grains, and to plug their pores. Both the natural and the synthetic surface modification resulted in steric and electrostatic stabilization of the clay particles, because of the highly charged, polyionic character of the surface-modifying organic matter. (C) 1998 Elsevier Science B.V. All rights reserved.