each other. As a result, the size ratio of the polyaniline to Isopycnic focusing is described by a physical model based on silica particles in this bidisperse suspension is very low.
equilibrium transport phenomena and derived from a general isoperichoric focusing theory. The model predicts the appearance of
2. THEORY the focusing phenomena in bidisperse suspensions of nanosize colloidal particles of very low average particle size ratio approaching
The focusing process requires the action of the positionone. This prediction is in contradiction with the generally accepted dependent field force, F i , which generates the macroscopic supposition that a density gradient-forming liquid should behave transport phenomena of the focused species i at velocity U i , as a continuum with respect to the focused species. Experimental verification of the theoretical approach was done by using a mix-which is also position dependent. Isoperichoric focusing (1), ture of polyaniline composite colored particles and silica composite in general, and isopycnic focusing (2), in particular, imply the particles. Polyaniline nanosize particles exhibited the focusing pheexistence of an effective property gradient of the carrier fluid nomenon in a density gradient formed by colloidal silica particles (the density gradient in the case of isopycnic focusing) which under the effect of centrifugal field forces. Comparison of the is either created coincidentally with the focusing processes or experimentally found concentration distribution of the polyaniline preformed beforehand. The dispersive processes act against both particles in the focused zone with the theoretically calculated disformation of the density gradient and the focusing transport tributions confirmed the reliability of the theory if silica interpartiuntil the steady state is reached. Although physically related, cle interactions are taken into account. ᭧ 1997 Academic Press the density gradient forming and focusing fluxes can be formally Key Words: theory of isopycnic focusing; nanosize polyaniline described, in a first approximation, as two independent procomposite particles; colloidal silica composite particles.
cesses. The total flux of all species within the system, j, has vectorial character and is the sum of the flux of the carrier liquid density modifier, j m , and the flux of the focused species, j f :