Neutron scattering study of colloidal interactions in an adsorbing polymer solution

Small-angle neutron scattering is used to study the interaction between the colloidal particles when they are suspended in an end-functionalized polymer solution. By matching the scattering length density of the solvent with that of the polymer, we measured the partial structure factor S-c(Q) of the colloidal particles. The measurements reveal that the polymer molecules in the colloidal suspension partition themselves between the bulk solution and the adsorbed state. The free polymer molecules in the solution induce a depletion attraction between the colloidal particles, but the magnitude of the attraction is suppressed considerably by the adsorbed polymer chains on the colloidal surfaces. It is found that the measured S-c(Q) can be well described by an effective interaction potential, which includes both the depletion attraction and the repulsion due to the polymer adsorption. The experiment demonstrates the effectiveness of using a polymer to control the colloidal interaction.