2022 Fiscal Year Research-status Report
原子間力顕微鏡による三相界線ナノ構造のダイナミック解析
| Project/Area Number |
21K14097
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| Research Institution | Kyushu University |
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Principal Investigator |
王 振英 九州大学, 工学研究院, 助教 (20896633)
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| Project Period (FY) |
2022-02-01 – 2024-03-31
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| Keywords | wetting dynamics / three phase contact line / droplet evaporation / capillary force / Marangoni flow |
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| Outline of Annual Research Achievements |
Extensive investigations have been carried out on the wetting dynamics of evaporative droplets, as the fact that the spreading and flow transition in volatile droplets remains controversial due to the complexity added by interfacial phase change and non-equilibrium thermal transport. We show, using both mathematical modeling and experiments, that the wetting dynamics of volatile droplets can be scaled by the spatial temporal interplay between capillary, evaporation, and thermal Marangoni effects. We quantify these complex interactions using phase diagrams based on detailed theoretical and experimental analyses. We further illustrate the spreading law of droplets by generalizing Tanner’s law (valid for non-volatile liquids) to a full range of liquids with saturation vapor pressure spanning from 101 to 104 Pa and on substrates with thermal conductivity spanning from 10-1 to 103 W/m/K. Besides its importance in fluid-based industries, the conclusions also enable a unifying explanation to a series of individual works including the criterion of flow reversal and the state of dynamic wetting, making it possible to control liquid transport in diverse application scenarios. The findings to date have been summarized and will be submitted recently.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Due to the limitation of time resolution of Atomic Force Microscopy on contact line tracing, we have shifted the exploration to the wetting dynamics of evaporative droplets with detailed investigations of the flow structure near the three-phase contact line. The research combines numerical simulation and experimental visualization. With a newly developed model and comprehensive experimental verifications, we are able to reach a big picture of the spreading dynamics of evaporative liquids on solids. Besides its importance in fluid-based industries, the conclusions also enable a unifying explanation to a series of individual works including the criterion of flow reversal and the state of dynamic wetting, making it possible to control liquid transport in diverse application scenarios.
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| Strategy for Future Research Activity |
In the next fiscal year, the flow structure near the three-phase contact line (TPCL) will be traced and comprehensively investigated with a micro-PIV setup based on an inverted fluorescence microscope. Especially, we will investigate the transition of the flow field near TPCL with stepwise increasing strength of interfacial phase change. The visualization results will be compared with the numerical data, which can provide rich information and elucidate the flow interaction (capillary flow and Marangoni flow) near TPCL. We will further conduct experiments on substrates with varying surface wettability or with wettability gradients, aiming to relate the flow field near TPCL with the visualized droplet dynamics as well as the deposition patterns.
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