In Situ Observation of Thermal Marangoni Convection on the Surface of a Sessile Droplet by Infrared Thermal Imaging

Abstract

An in situ observation method to understand thermal Marangoni convection in sessile droplets is reported in this paper. Infrared (IR) thermal imaging is applied in the experiments to visualize the transient temperature distribution on the surface of the droplet. Additionally, micro particle image velocimetry (micro-PIV) system illustrates the fluid field inside the droplet. Two kinds of droplets are considered in this paper: sessile droplets heated with a hotplate and droplets heated by an electrode at the apex. Convection in both droplets is observed in situ, and the experimental results are in accord with the theory of fluid mechanics.

Keywords:

• Electrowetting
• Marangoni convection
• sessile droplet
• infrared thermal imaging

Acknowledgements

This work was jointly supported by National Natural Science Foundation of China (NSFC, Grant Nos 11072244 and 60936001) and Instrument Developing Project of the Chinese Academy of Sciences (Grant No. Y2010031). The authors are grateful to Prof. Li Duan and Dr Lujun Li from the National Microgravity Laboratory, Institute of Mechanics, Chinese Academy of Sciences, for fruitful discussions. The authors are also thankful to Mr Xiaozhuo Zhai from the Fluke Corporation for the invaluable support in the use of various equipments.