A small-angle neutron scattering study of the structure of gelatin at the surface of polystyrene latex particles

Small-angle neutron scattering has been employed to investigate the effects of salt and pH on the structure of gelatin at the surface of negatively charged polystyrene latex particles. Measurements were made with the scattering length density of the particles matched with the solvent. The data have been fitted to a combination of the scattering due to the average volume fraction profile of the layer and scattering from spatial concentration fluctuations. It has been shown that the scattering from the bare latex particles, the gelatin in solution, and the adsorbed layer have very different forms. The difference in the gelatin scattering indicates a significant change in the structure of the polymer on adsorption. The volume fraction profiles derived from the fits show that, on increasing the pH, the concentration of chains at the interface decreased but the extension of the chains from the surface increased. Varying the ionic strength of the continuous phase gave unexpected results.