Optothermal oscillation of hollow microparticles near a droplet surface

The optothermal oscillator is an important optofluidic technology. In this study, we explore an optothermal approach to achieve a microparticle oscillator near the fluid surface of a droplet. The microparticles used are hollow borosilicate microparticles. The motion of these particles is primarily governed by laser-induced Marangoni convection and capillary forces at the droplet's surface. Initially, the particles are positioned near the top of the droplet. As the laser beam illuminates the droplet surface, the resulting Marangoni convection pulls the particles away from the droplet's apex. When the laser is blocked, capillary forces restore the particles to their original position near the top of the droplet. The laser's switching mechanism is achieved through a motor-controlled mechanical intervention. Our research introduces an approach for oscillating colloidal particles near a droplet's surface, offering promising applications in the field of microparticle manipulation.