Effects of Photothermal Conversion on the Laser-Photophoresis of Micro-Particles in Liquid Media.

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Laser-Photophoresis is a promising technique to migrate and to separate microparticles in liquid media. However, the effect of photothermal conversion on the photophoretic behavior of photo-absorbing microparticles is still ambiguous. In this research project, we have made the following studies to elucidate the effect of photothermal effects on the laser-photophoretic migration of microparticles. 1. Laser Photophoretic Migration with Periodic Expansion-Contraction Motion of Photo-Absorbing Microemulsion Droplets in Water. : It was elucidated that the origin of the motion is photothermal conversion and the mechanism of the periodic expansion-contraction motion is consisted of three steps. 2. Temperature Distribution in the Laser-Irradiated Droplet in Water. : The temperature of the front-side of the irradiated droplet is higher than that of the back-side of the droplet. This temperature distribution results in the reverse photophoresis. 3. Separation of Blood Cells by Laser-Photophoresis. : We proposed the method for the photophoretic separation of red blood cells and white blood cells. 4. Formation and Trapping of Bubbles in the Organic Solvents. We found new phenomena that the laser induces the formation of bubble in organic solvents and the bubble can be trapped by the laser beam. 5. Photophoretic behaviors of water droplets and aqueous solution droplets in organic solvents. : It was found that water absorbs 1064 nm laser light and this causes complex photophoretic behavior of aqueous droplets in organic solvents. These behaviors cannot be explained by the simple Mie scattering model