POTENTIAL-BARRIER FIELD-FLOW FRACTIONATION: POTENTIAL CURVES AND INTERACTIVE FORCES

Abstract

ABSTRACT Potential-barrier field-flow fractionation (PBFFF), a tool for the separation and size characterization of colloidal particles is based on the variation of the surface forces in the FFF process, which control particle adsorption–desorption on the channel wall. The latter phenomena depend on the total potential energy of interaction between the colloidal particles and the channel wall. Our results suggest, that at high ionic strengths of the suspending medium, the colloidal particles used (submicron monodisperse spherical particles of hematite and titanium dioxide) are retained within the secondary minimum even though the energy barrier is sufficiently high to inhibit attachment in the primary minimum of the interaction energy curve. This hypothesis is further supported by the particle detachment experiments at low ionic strengths of the suspension in which the total number of adhered particles was revealed when the secondary minimum was eliminated. The secondary minimum energies, φmn1, necessary for the separation of the colloidal particles used in PBFFF, which were computed using the electrical double layers and van der Waals expressions were found, approximately, in the range −4.7<φmn1<−3.2 kT, even though the energy maxima were much greater (φmax≈109 kT). As the secondary minimum energies depend not only on the size of the particles, but also on their nature, one could separate by PBFFF particles of different size, as well as of the same size but with different chemical constitution.