| dc.description.abstract | With the rapid development of microfluidic technology, surface tension will become an important factor in the driving of fluids at this time, and the liquid thermocapillary driving of the difference in surface tension due to temperature gradient has become a topic that needs to be considered in many fields today. In the past, scholars have conducted considerable research on thermocapillary force. It is generally believed that the larger the volume and diameter of droplet, which can produce a better thermocapillary effect. However, in some cases, the fluid viscosity and hysteresis will offset them and make the liquid unable to move. Therefore, the pre-deformation of the liquid droplet is used to observe the influence of the thermocapillary force, hysteresis force and viscous force on the thermocapillary driving the liquid droplet, in order to achieve the effect that the large-volume liquid droplet can produce the thermocapillary phenomenon.
In this paper, the compression release process is used to produce pre-deformed liquid droplets of different diameters under the condition of a fixed liquid droplet volume, and the large-volume pre-deformed paraffin oil droplets are driven by thermocapillary force on a smooth silicon wafer. It was found that the back edge of the non-pre-deformed liquid droplet with a diameter of 6 mm would spread in the early stage and the appearance was severely deformed. When the small diameter pre-deformed liquid droplet which no spread will occur, but the front edge will undergo capillary shrinkage and the back edge will remain stationary. After the diameter reaches 9 mm or more, the thermocapillary phenomenon is successfully generated at the rear edge, but the front edge still occasionally shrinks. In order to understand this situation, the thermocapillary driven mechanical model is used to analyze the pre-deformed liquid droplets. It is found that liquid droplets with diameters of 9, 10.5 mm will generate an inward compression force at both edges after heating. It is speculated that the liquid droplets will be in a new quasi-steady state after the compression and release process at the beginning, and therefore the wettability will increase, while the pre-deformed liquid droplets will be released from the quasi-steady state once heated, and the liquid droplets will tend to return to their original state, causing both edges to produce capillary contraction, and such capillary contraction behavior for the thermocapillary drive will become a boost at the rear edge and a resistance at the front edge, while the capillary force at the rear edge counteracts part of the viscous force to generate a thermocapillary drive. | en_US |