Studies of electrical double-layer interactions in concentrated silica sols by small angle neutron scattering

Effects of ionic strength, volume fraction and pH on the interparticle interactions in concentrated silica sols of different particle size have been investigated by small-angle neutron scattering. The results have been modelled using the solution of the mean spherical approximation (MSA) of Hayter and Penfold and Hansen and Hayter. In this model the pair potential comprises a hard core and a soft tail, due to the screened coulombic repulsion between the electrical double layers surrounding the spherical particles. Closed analytic solutions of the structure factor, S(Q), for this potential have been used in the fits to the experimental scattering data to obtain the surface charge and potential of the silica particles. Although the surface charge so obtained rises with increases in the pH of the sols, as expected, values are markedly less than the total surface charge density of silica as previously reported

Small angle neutron scattering studies of silica sols in water at high temperature

The temperature dependence of the interparticle interactions in a silica sol have been investigated in the range 298-533 K by small-angle neutron scattering. By applying the rescaled mean spherical approximation (MSA), due to Hansen and Hayter, closed analytic solutions of the structure factor, S(Q), for a screened coulombic potential have been fitted to experimental scattering data to obtain the effective surface charge and potential of the silica particles. As the temperature is increased, marked reductions in the interaction potential are observed, which are partially restored on cooling. These effects are ascribed to the considerable changes in the dielectric properties and ionic dissociation of water that occur at these elevated temperatures