ON THE POSSIBILITY OF PHOTOPHORETIC FIELD-FLOW FRACTIONATION

The direct and indirect mechanisms of particles photophoresis are cons idered theoretically. The motion of micrometer-size particles (latex s pheres, glass beads, carbon black particles) in water under the action of focused Ar + -ion laser beam (lambda = 514.5 nm) was studied exper imentally in two arrangements. First, the particles' motion was observ ed using a microscope, and their photophoretic velocities were evaluat ed. The positive photophoresis (away from the light source) was observ ed for all kinds of particles, the photophoretic velocities being depe ndent on the size and optical properties of particles and on the laser power density. In the second arrangement, the laser beam was focused at the entrance glass window of a round metallic capillary, in the dir ection of suspension flow inside the capillary. The elution curves of injected samples of polydisperse carbon black particles were registere d using a UV detector in the sedimentation-gravity field-flow fraction ation (FFF) conditions with and without laser light action. Typical cu rves had a strong initial maximum corresponding to small particles fra ctions and a considerably lower secondary maximum corresponding to lar ge particles. The laser light action changed the shape of the initial maximum and shifted the secondary one to a smaller time. The results s how that photophoretic velocities of particles, which can be generated under FFF conditions, are sufficient to accomplish particles separati on relative to their size and optical properties. (C) 1997 John Wiley & Sons, Inc.