Droplet Migration and Coalescence in a Microchannel Induced by the Photothermal Effect of a Focused Infrared Laser

In this work, the localized photothermal effect of a focused infrared laser-induced migration and coalescence of the droplets in a microchannel was visually studied. Experimental results showed that upon laser irradiation, the droplet was actuated to move away from the fixed laser spot because of the surface tension gradient resulting from the localized heating effect. Initial droplet moving velocity first increased and then decreased as the laser spot changed from the droplet ellipsoid region to the center. Larger laser power and shorter droplet length resulted in a higher initial droplet moving velocity. Moreover, use of the proposed method allowed the coalescence of the droplets via moving the laser spot. There existed a maximum laser spot moving velocity to allow for the occurrence of the coalescence of the droplets, which depended on the laser power and droplet length. Larger laser power and smaller droplet length yielded higher maximum laser spot moving velocity for the coalescence of the droplets.

Automated summary

This study visually examined the localized photothermal effect of a focused infrared laser on droplets in a microchannel. Results showed that laser irradiation caused droplets to move and coalesce, with initial movement velocity depending on laser power and droplet length. Higher laser power and shorter droplet length resulted in faster movement and coalescence of the droplets.