On the possibility of photophoretic field‐flow fractionation

Abstract

The direct and indirect mechanisms of particles photophoresis are considered theoretically. The motion of micrometer-size particles (latex spheres, glass beads, carbon black particles) in water under the action of focused Ar+-ion laser beam (λ=514.5 nm) was studied experimentally in two arrangements. First, the particles' motion was observed using a microscope, and their photophoretic velocities were evaluated. The positive photophoresis (away from the light source) was observed for all kinds of particles, the photophoretic velocities being dependent 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 direction of suspension flow inside the capillary. The elution curves of injected samples of polydisperse carbon black particles were registered using a UV detector in the sedimentation-gravity field-flow fractionation (FFF) conditions with and without laser light action. Typical curves had a strong initial maximum corresponding to small particles fractions and a considerably lower secondary maximum corresponding to large particles. The laser light action changed the shape of the initial maximum and shifted the secondary one to a smaller time. The results show that photophoretic velocities of particles, which can be generated under FFF conditions, are sufficient to accomplish particles separation relative to their size and optical properties. © 1997 John Wiley & Sons, Inc. J Micro Sep 9: 321–327, 1997