Transient behavior of adsorbing/adsorbed polyelectrolytes on the surface of colloidal particles studied by means of trajectory analysis of Brownian motion

Direct movie analysis of single colloidal particles undergoing Brownian motion was applied to the colloidal particle adsorbed with polyelectrolytes. This method allows the direct observation of the movement of single colloidal particles with time resolution of 0.1 s. Analysis was performed on the basis of Stokes–Einstein relation applied to the Brownian trajectory of single particles. The comparison of the diffusion constant of spherical polystyrene latex particles with and without polyelectrolyte addition clearly demonstrates the increment of hydrodynamic diameter due to adsorption of polyelectrolytes. This increment was the same magnitude as that of polyelectrolytes in solution. It was also found that the determined layer thickness decreases dramatically as a function of elapsed time with time scale of several ten minutes. This time scale decreases with an increase of ionic strength. However, the result of electrophoretic mobility keeps almost constant irrespective of ionic strength with a time scale longer than several hours.