隨著微流體技術的快速發展，此時表面張力將成為主導流體驅動的重要因素，而因溫度梯度產生表面張力差的液體熱毛細力驅動也就成為了現今許多領域需要考慮的議題。過去學者們對熱毛細力已有相當程度的研究，普遍認為體積越大的液珠其直徑越大，能有更好的熱毛細力驅動效果。然而在某些情況下，流體黏滯力與遲滯力會將其抵銷導致液體無法移動。為此利用液珠預變形的方式觀察熱毛細力、遲滯力以及黏滯力之間對於熱毛細力驅動液珠的影響，以期望達到大體積液珠能產生熱毛細力驅動的效果。
本文利用壓縮釋放過程在液珠體積固定的情況下，製作出不同直徑大小的預變形液珠，並於光滑矽晶圓上以熱毛細力驅動大體積之預變形石蠟油液珠，再與無預變形之液珠相互比較。發現無預變形直徑6 mm之液珠後端會在前期因溫度而引起擴展並且外觀嚴重變形。預變形液珠於小直徑時不會有擴展發生，但前端會發生毛細收縮，後端靜止不動。而直徑到達9 mm以上後，後端成功產生熱毛細力驅動現象，前端卻依然時而發生毛細收縮。為了解這樣的狀況，利用熱毛細力驅動力學模型對預變形液珠進行分析。發現預變形之液珠會在加熱後於兩端產生一股向內壓縮的力。推測一開始液珠經過壓縮釋放過程後會處於一個新的準穩態因此潤濕性增加，而預變形液珠一經加熱則準穩態解除，液珠會傾向回復到原本的狀態造成兩端產生毛細收縮，而這樣的毛細收縮行為對於熱毛細力驅動來說會在後端成為助力，前端成為阻力，而在後端毛細力與部分黏滯力抵銷，產生熱毛細力驅動。

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.

[1] A. Kundan, J. L. Plawsky, P. C. Wayner Jr., D. F. Chao., R. J. Sicker, B. J. Motil, T. Lorik, L. Chestney, J. Eustace, and J. Zoldak, ” Thermocapillary phenomena and performance limitations of a wickless heat pipe in microgravity,” Physical review letters, Vol. 114, pp. 146105, 2015.
[2] W. Wilkens, “Contamination danger by oil-lubricated ball beatings in spacecraft,” J. Spacecraft Rockets, Vol. 8, No. 9, pp. 962 - 965, 1971.
[3] S. S. Kalichetty, T. Sundararajan, and A. Pattamatta, “Thermocapillary migration and interaction dynamics of droplets in a constricted domain,” Physics of Fluids, Vol. 31, pp. 022106, 2019.
[4] R. Wang and S. Bai, ” Modeling, and experimental analysis of thermocapillary effect on laser grooved surfaces at high temperature,” Applied Surface Science, Vol. 465, pp. 41 - 47, 2019.
[5] J. B. Brzoska, F. B. Wyart, and F. Rondelez, “Motions of droplets on hydrophobic model surfaces induced by thermal gradients,” Langmuir, pp. 2220 - 2224, 1993.
[6] G. Karapetsas, N. T. Chamakos, and A. G. Papathanasiou, “Thermocapillary Droplet Actuation: Effect of Solid Structure and Wettability,” Langmuir, Vol. 33, pp. 10838 - 10850, 2017
[7] D. T. Wasan, A. D. Nikolov, and H. Brenner “Droplets speeding on surfaces,” Science, Vol 291, pp. 605 -606, 2001.
[8] H. Liu and Y. Zhang, ” Modelling thermocapillary migration of a microfluidic
70
droplet on a solid surface,” Journal of Computational Physics, Vol. 280, pp. 37 - 53, 2015.
[9] H. B. Nguyen and J. C. Chen, “A numerical study of thermocapillary migration of a small liquid droplet on a horizontal solid surface,” Phys. Fluids, Vol. 22, pp. 062102, 2010
[10] Q. Dai, M. M. Khonsari, C. Shen, W. Huang, and X. Wang, “Thermocapillary migration of liquid droplets induced by a unidirectional thermal gradient,” Langmuir, Vol. 32, No. 30, pp. 7485 - 7492, 2016.
[11] S. J. Hong, T. H. Chou, S. H. Chan, Y. J. Sheng, and Heng-Kwong Tsao”Droplet compression and relaxation by a superhydrophobic surface: contact angle hysteresis,” Langmuir, Vol. 28, pp. 5606 - 5613, 2012.
[12] Q. Dai, Y. Ji, Z. Chong, W. Huang, and X. Wang, “Manipulating thermocapillary migration via superoleophobic surfaces with wedge shaped superoleophilic grooves,” Journal of Colloid and Interface Science, Vol. 557, pp. 837 - 844, 2019.
[13] T. Young, ”An essay on the cohesion of fluids,” Philosophical Transactions of the Royal Society of London Vol. 95, pp. 65 - 87, 1805.
[14] A. Cecere, R.D. Paola, R. Savino, Y. Abe, and L. Carotenuto,and S.V. Vaerenbergh, ” Observation of Marangoni flow in ordinary and self-rewetting fluids using optical diagnostic systems,” Eur. Phys. J. Special Topics,Vol. 192, pp. 109 - 120, 2011.
[15] W. R. Jones Jr and L. D. Wedeven, “Surface-tension measurements in air of liquid lubricants to 2000 c by the differential-maximum-bubble- pressure technique,” Nasa technical note, NASA TN D-6450, 1971.
71
[16] Q. Dai, W. Huang, X. Wang, and M. M. Khonsari, “ Contact Angle Hysteresis Effect on the Thermocapillary Migration of Liquid Droplets,” Journal of Colloid and Interface Science, Vol. 515, pp. 32 - 38, 2018.
[17] M. K. Smith, “Thermocapillary migration of a two-dimensional liquid droplet on a solid surface,” J. Fluid Mech, Vol. 001, No. 294, pp. 209 - 230, 1995.
[18] L. M. Hocking, “The spreading of a thin drop by gravity and capillarity,” Q. Jl Mecb. appl. Math., Vol. 36, pp. 1, 1983.