In this study, we investigated the formation of air-rich microbubbles through local photothermal heating of non-degassed water. When non-degassed water is locally heated, vapor-rich bubbles are initially formed. These bubbles have a maximum radius of approximately 9 μm and stabilize while oscillating and exhaling air-rich bubbles. However, when the exhaled bubbles fuse and grow, they revert to vapor-rich bubbles on the heat source. The vapor-rich bubbles are then exposed to a large amount of air, causing them to transition to air-rich bubbles. In this paper, the motion of the exhaled air-rich bubble is explained by the drag force owing to the flow and the Marangoni force owing to the temperature gradient acting on the bubble. Because the drag force is proportional to the bubble radius, and the Marangoni force is proportional to the square of the bubble radius, the larger the bubble, the stronger the effect of the Marangoni force. Thus, as the bubbles grow, they are drawn toward the heat source against the flow created by the vapor-rich bubbles. These results are useful for a better understanding of bubble growth and determining the conditions for the stable formation of vapor-rich bubbles in non-degassed water.
Upstream motion of oil droplets in co-axial Ouzo flow due to Marangoni forces
Technische Universität Darmstadt（达姆施塔特工业大学）；University of Twente（特文特大学）；SLAC National Accelerator Laboratory（斯坦福直线加速器中心）；Max Planck Institute for Dynamics and Self-Organization（马克斯·普朗克动力学与自组织研究所）
Surfactant-loaded capsules as Marangoni microswimmers at the air-water interface: Symmetry breaking and spontaneous propulsion by surfactant diffusion and advection
