THE DIELECTROPHORETIC LEVITATION OF LATEX BEADS, WITH REFERENCE TO FIELD-FLOW FRACTIONATION

Interdigitated microelectrodes have been used to investigate the passi ve dielectrophoretic levitation of latex beads as a function of the fr equency and voltage of the applied electrical signal, the suspending m edium conductivity, bead size and characteristic dimensions of the ele ctrodes. The variations of the electric field strength E and of the fa ctor del E-2 as functions of the height above the electrode plane were determined by computer-aided modelling, As predicted from a simple th eory based on the balancing of the gravitational settling force with t he negative dielectrophoretic force, the height of levitation was foun d to be independent of the bead size and at 1 MHz, at which the levita tion was at its largest, to be only weakly dependent on the conductivi ty of the suspending medium, The frequency dependence of the levitatio n height was found to be in close agreement with theory, based on the known dielectric properties of the beads and on previously determined electrode polarization effects. Apart from using this method to invest igate the dielectric properties of particles, a particularly important application is envisaged to be that of particle separation, based on differences in dielectric properties, using dielectrophoretic levitati on in combination with field-flow fractionation techniques.