Journal of Colloid and Interface Science, Vol.229, No.2, 462-476, 2000
Effect of ionic and nonionic solutes on the transient and steady states in the settling of charged colloidal particles
Centrifugation was applied to study the transport phenomena in various suspensions of charged colloidal silica particles. Isopycnic focusing of colored density marker beads was used to view the evolution of the density gradient and to determine its steady-state shape from the measured positions of the focused zones. The effect of the ionic and nonionic solutes on the transient and steady states was studied. The experimental results are discussed in relation with the published theoretical dependence of the transport coefficients on the volume fraction of the settling particles, The understanding of the transport phenomena and of the interfering particle interactions governing the formation of the density gradient and the subsequent isopycnic focusing under model static conditions is necessary for the optimization of the isoperichoric focusing held-how fractionation dynamic experiments, but it should allow a more accurate description of the relaxation phenomena and retention in polarization field-flow fractionation as well. Some previous experimental results concerning the study of the transport phenomena of the charged silica particles in an electric field are exploited here to demonstrate the general character of the observed behavior, independent of the field nature.
Keywords:colloidal silica;settling in a centrifugal field;settling in an electric field;kinetics of transient state;sedimentation steady-state of charged and screened particles