Interparticle forces in montmorillonite gels

Abstract

Aqueous dispersions of homoionic sodium montmorillonite have been studied under compressive and decompressive conditions in order to determine the internal pressure of the system as a function of the clay and electrolyte concentrations. Complementary measurements were also made of the electrokinetic properties of the montmorillonite particles. Compression of a sodium montmorillonite dispersion from ca. 2 % to ca. 65 % w/w gave a continuous curve of pressure against distance of plate separation up to pressures greater than 100 atmospheres. On subsequent decompression, however, a different curve was obtained and a hysteresis effect was found to occur in the pressure against distance curves. It is considered that the initial curve represents the behaviour of a disordered clay system, i.e., the initial gel, whereas the decompression curve represents the behaviour of a system in which the plates have become ordered into a parallel array. The elastic modulus of the latter system was determined. The results strongly suggest that the gel properties of montmorillonite dispersions are the consequence of long range electrostatic interactions.