3D manipulation of vapor microbubbles driven by the Marangoni force

We show the 3D quasi-steady-state trapping of ethanol vapor microbubbles and their real-time manipulation in liquids driven by the Marangoni force that is triggered by using a low-power continuous-wave laser. The light absorption phenomenon, caused by the silver nanoparticles photodeposited on the core of optical fibers, is employed for both the generation of vapor microbubbles and triggering the Marangoni effect. The thermal effects, activated by either the silver nanoparticles on the optical fiber's core or the light bulk absorption, modulate the surface tension of the bubble wall, generating longitudinal and transversal forces, similar to the optical ones. The balance of the optothermal forces drives the quasi-steady-stated 3D manipulation of microbubbles. By numerical simulations, we acquire expressions for the temperature profiles and present analytical expressions for the Marangoni force. Moreover, using an array of three fibers with photodeposited nanoparticles is used to demonstrate the transfer of bubbles from one fiber to another by sequentially switching on and off the lasers.