Periodic Expansion-contraction Motion of Photoabsorbing Organic Droplets during Laser Photophoretic Migration in Water

Laser photophoretic behavior of 2-benzylpyridine droplets including Co(III)-pyridylazo complex as a photoabsorber was examined in water by irradiating cw Ar+ ion laser. We have made a new observation like a “breathing” motion that the droplets repeated the expansion and the sudden contraction during laser photophoretic migration. The period of the motion decreased with increasing the Co complex concentration in the droplet and also with increasing the laser power. The origin of the motion is the water vaporization in the droplet by photothermal conversion.