Macroscopic swelling of clays derived from homogenization

摘要

Swelling clay consists of large flat sheets of deformable silicate structures separated from one-another by an aqueous layer (adsorbed water) [1]. Each clay mineral consists of a 2:1 layer consisting of an octahedral aluminia sheet between two silica tetrahedral sheets. Crystal imperfections and isomorphous substitutions in the smectitic minerals produce negative surface charge density which is neutralized by exchangeable cations to form a diffuse positively ionic atmosphere around the clay mineral surfaces. Swelling phenomena result for change in the crystal dimension when water is incorporated into the lattice structure. When a phyllislicate crystal is put in contact with water, the water penetrates between the superimposed layers and intermolecular forces (hydration and electrical repulsive forces) operate to disjoin the stacked silicate layers. During water uptake, the volume of montmorillonite increases by absorbing water. Water will flow osmotically into regions of higher ionic concentration and particles will separate causing swelling. For low moisture content range (interstices smaller than 50A) swelling is dominated by hydration forces, which consist of bonding forces between the mineral surfaces and the water which arise form the hydrophilic structure of the platelets resulting from the ordering of polar water molecules near the clay minerals (Israelachvili [2]). In contrast, for long-range interactions, swelling is dominated by the electrostatic effect, which is classically governed by the conventional Gouy-Chapman theory of diffuse double layer wherein the equilibrium charge distribution and the electrical field are governed by a Poisson-Boltzman equation [3].