Thermal-lensing measurement of particle thermophoresis in aqueous dispersions

We show that thermophoresis (particle drift driven by thermal gradients) in aqueous solutions can be measured by using an all-optical thermal-lensing setup, where a temperature gradient is set by a near-infrared laser beam with no need of light-absorbing dyes. After discussing the principles of the method, we study by numerical simulation the nature and extent of parasitic thermal-convection effects, and we describe an optical setup designed to limit them. We finally present preliminary results on thermophoresis in micellar solutions and colloidal dispersions. (C) 2004 Optical Society of America.