| The stability of colloidal suspensions depends on the colloidal force interactions between particles. These forces include Brownian motion, van der Waals attraction, electrostatic repulsion, and steric force interactions. Properties of suspensions may be characterized by spectroscopic techniques, light scattering, electrophoreses, sedimentation, rheology, and various other methods. In this work, the stability of silica suspensions is manipulated by adjusting the electrolyte concentration and by adding an adsorbing polymer (polyethylene oxide). The stability of these suspensions is investigated using time-dependent UV-visible spectrophotometry which can characterize the sedimentation behavior. In stabilizing the suspensions using an adsorbing polymer, the concentration and molecular weight of the polymer as well as the sample preparation procedure seem to play a vital role in maintaining, re-establishing, or preventing suspension stability.;If the colloidal suspensions are dilute, as in the sedimentation study, their settling behavior is predictable theoretically, and the concentration profile of the settling particles can be described as a function of time and vertical distance by an analytical expression. By studying the particle concentration as a function of time at fixed vertical positions, the average particle size can be estimated. Therefore, UV-visible spectrophotometry may also serve as a method to characterize particle size distributions.;The complex rheological behaviors of colloidal suspensions result from colloidal forces as well as from hydrodynamic interactions. The particle size distribution also plays an important role. Under a fixed physicochemical condition, the shear viscosity of an electrostatically stabilized small particle monodisperse suspension is always higher than that of a large particle monodisperse suspension since the relative thickness of the electrical double layer is larger for the small particles. For concentrated bidisperse suspensions in which two different size particles are mixed in different proportions, the viscosity of the bidisperse suspensions is lower than either one of the monodisperse suspensions. This behavior, which was investigated through a standard rheological measuring technique, is apparently associated with changes in the microstructures of the suspensions as the relative concentrations of the two particles are varied. |
