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Thermochromic visualization of the heated region around a microbubble during Marangoni flow generation
Journal of Nanophotonics ( IF 1.5 ) Pub Date : 2021-02-01 , DOI: 10.1117/1.jnp.15.016007
Kyoko Namura 1 , Toshiki Sono 1 , Samir Kumar 1 , Kaoru Nakajima 1 , Motofumi Suzuki 1
Affiliation  

We experimentally investigated simultaneous microfluidic control and visualization of a heated region using gold nanoisland/VO2 thin films. By focusing a laser on the film, we photothermally generated an air microbubble in nondegassed water. After the bubble generation, another laser spot was irradiated 48 μm away from the bubble center. As a result, a sudden onset of the rotational Marangoni flow was observed at 130 ms after the laser was turned on. At the same time, the heated region above 70°C was visualized based on the thermochromic property of the thin film. The heated area did not vary significantly at the onset of the flow, indicating that there is a threshold temperature or temperature gradient on the bubble surface for generating the rotational Marangoni flow. To understand the flow generation, we decreased the distance between the bubble and the laser spot. The resulting visualized heated region suggests that a part of the bubble surface has to be heated above 70°C to generate the rotational flow. In addition, the heated area during the flow generation remained small as the distance decreased. The gold nanoisland/VO2 thin film is suitable for understanding and optimizing the rapid Marangoni flow generation.

中文翻译:

Marangoni流动产生期间微泡周围加热区域的热致变色可视化

我们实验研究了同时使用金纳米岛/ VO2薄膜的微流控和加热区域的可视化。通过将激光聚焦在胶片上,我们在不脱气的水中光热产生了一个空气微气泡。气泡产生后,在距气泡中心48μm处照射另一个激光点。结果,在打开激光后的130 ms处观察到旋转的Marangoni流突然开始。同时,基于薄膜的热致变色特性,可以看到高于70°C的加热区域。流动开始时受热面积没有明显变化,表明在气泡表面上存在阈值温度或温度梯度以产生旋转的马兰戈尼流。要了解流程的产生,我们减小了气泡和激光点之间的距离。最终的可视化加热区域表明,必须将气泡表面的一部分加热到70°C以上才能产生旋转流。另外,随着距离的减小,在流动产生期间的加热面积保持较小。金纳米岛/ VO2薄膜适合于理解和优化快速的Marangoni流生成。
更新日期:2021-02-19
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