Long-time self-diffusion of spherical colloidal particles measured with fluorescence recovery after photobleaching

Long-time self-diffusion coefficients in concentrated colloidal dispersions of silica spheres, with various interaction potentials, were measured with the fluorescence recovery after photobleaching technique. Charge stabilized spheres were measured in solutions of LiCl in dimethylformamide with varying ionic strength. Sterically stabilized hard-sphere-like stearyl silica dispersions were studied in cyclohexane. The fluorophore used, fluorescein-isothiocyanate, was covalently attached to the surface of the spheres (for the charged particles) or buried inside the silica core (for the hard spheres). The particles were characterized by electrophoresis, static and dynamic light scattering, and transmission electron microscopy. The experimental results are discussed and compared with existing theories on long-time self-diffusion.