Small-angle neutron scattering study of concentrated colloidal dispersions: the interparticle interactions between sterically stabilized particles.

Small-angle neutron scattering (SANS) was used to investigate the interparticle interactions in concentrated dispersions of colloidal silica stabilized either by steric or by electrostatic repulsive interactions. In 10 mM NaCl, an adsorbed PEO layer is required to prevent flocculation, and particles are stabilized by steric repulsions. The adsorbed layer was made invisible to neutrons by contrast matching with the aqueous continuous phase. Dispersions of the same particles at the same concentrations but in the absence of added salt and adsorbed PEO were also studied. In both cases, the SANS spectra of concentrated dispersions show a peak at low Q, which is due to interparticle interactions: a structure factor. The SANS data can be described rather well by a homogeneous spherical form factor and a structure factor based on the Hayter-Penfold/Yukawa potential model. The steric potential was compared to the electrostatic potential obtained by fitting the SANS data of the bare silica dispersions. The steric potential shows a greater dependence on the particle volume fraction, which we ascribe to the penetration and compression of the adsorbed PEO layer as the particles approach.