Light scattering investigation of amphiphile and polymer adsorption on the surface of colloidal particles with low optical contrast

Abstract

We have exploited the peculiar optical properties of fluorinated polymer colloids, which have a very low refractive index and a partially crystalline internal structure, to obtain accurate adsorption isotherms by combining static and depolarized dynamic light scattering information. Due to the very weak optical contrast between perfluoropolymers and water, the intensity of the light scattered by suspensions of fluorinated colloids strongly depends on the presence of surface adsorbates. At the same time, the depolarized scattering contribution arising from the particle internal optical anisotropy allows to measure the rotational diffusion constant which is strongly dependent on the particle hydrodynamic radius. We have applied such technique to measure the adsorption isotherms of both nonionic and ionic surfactants, and of long-chain block copolymers.