caused by diffusion, Brownian motion, interparticle repul-Various effective field forces can generate the concentrating flux sions, etc. The system approaches the quasi-equilibrium state of the colloidal particles. Centrifugal field forces were used in this at which the concentrating transport and random dispersive work to study the kinetics of the transport phenomena and the migration counteracting fluxes are balanced. The large coleffect of interparticle interactions of the model silica suspension. ored particles of known densities mixed with the colloidal Isopycnic focusing of the colored density marker beads was used particle suspension focus at their isopycnic positions and to visualize the evolution and final quasi-equilibrium shape of the can be used as density markers to determine optically the density gradient formed in silica suspension. Many operational shape of the density gradient and its evolution in time. The parameters and experimental conditions (thickness of the liquid transient period between the initial uniform spatial distribulayer in measuring cells, intensity of the centrifugal forces, average concentration of the silica particles, and geometrical shape of the tion of the colloidal particles and the quasi-equilibrium state measuring cells) were tested to evidence their influence on the with a quasi-stationary density gradient is of crucial imporconcentration and density gradient formation. The main objective tance to the duration of the isopycnic focusing separations. was to apprehend the processes governing isoperichoric focusing The short migration distance in the direction of the concenin thin layers under model static conditions which is necessary for trating flux, as in static (without flow) thin-layer isopycnic the optimization of isoperichoric focusing field-flow fractionation focusing (TLIF), results in a short separation time. TLIF is dynamic experiments carried out under conditions of hydrodya new analytical technique proposed recently (1). namical flow as an active factor of the separation by focusing An understanding of the kinetic aspects of the transient effect. The experimental results were compared with the hypothetstate under static conditions should allow optimization of ical model of noninteracting particles to demonstrate the effect of the operational conditions of the dynamic separation systems the actual interparticle interactions.