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.