Migration Characteristics of Bubble Manipulated by Photothermal Marangoni Effect(<Special Issue>The 1st Symposium on Micro-Nano Engineering)

Recently, the microfluidic device such as μ-TAS has been attracted in many fields. Since surface forces become dominant with decreasing of a length scale, it is difficult to remove the bubble attached to the channel in a device. An unexpected adhesion of a bubble causes the large pressure loss or deterioration of the device. We have suggested the noncontact bubble manipulation method using photothermal Marangoni effect. When the fluid in the vicinity of the bubble is irradiated by the laser and local temperature gradient is induced around the bubble, Marangoni convection along the gas-liquid interface occurs due to the surface tension gradient. As a result, the bubble migrates to the laser spot and scanning of the laser spot enables transportation of the bubble. In this paper, the migration behavior of the bubble along the channel was investigated. We also obtained the minimum optical power for the manipulation with different conditions of bubble sizes, scanning speed and kinematic viscosity of liquid. Experimental results can be summarized by a dimensionless number which means a ratio of thermocapillary force to viscous drag force. Universal criteria on migration are indicated by the dimensionless number.