Studies on silica sol-clay particle interactions by small-angle neutron scattering

SANS data were collected on a series of hydrolyzed silica and silica-clay complexes prepared from a 40 Å silica sol and aqueous suspensions of Na⁺ montmorillonite. The hydrolyzed silica product showed a peak centered at Q = 0.0856 Å^-1 corresponding to a distance of 73 Å between the sol particles. For such an evaporated gel in which the particles are in close contact, this distance is expected to be very close to the particle diameter indicating partial aggregation of the original spheres. A similar feature was observed in the SANS data for silica-clay products indicating the presence of some unintercalated silica. The intensity of this scattering was found to be dependent on the silica:clay ratio and the reaction time. The SANS data in the region from Q = 0.006 to 0.025 Å-¹ were characteristic of clay scattering and exhibited a power-law behavior. The change in the slope of this curve upon reaction of the clay with the silica sol was interpreted in terms of a separation of clay platelets caused by a binding interaction with the sol particles.