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Dynamiques de gouttelettes mouillantes

Abstract : This work presents the dynamics of liquid microdroplets deposited on a substrate in the case of complete wetting, when another process interferes with spontaneous spreading.

The first chapters, the main part of this manuscript, is devoted to the coupling between spreading and evaporation of a volatile liquid. Experiments were previously done by R.D. Deegan with pure water droplets deposited on freshly cleaved mica ten years ago. The receding dynamics of the contact line cannot be fully explained by a simple theory based on aerosol physics. Water is a very caracteristic fluid and mica is a ionized surface, this work was done again with more conventional fluids (like alkanes) and
substrates with which they haven't any specific interaction with the liquids used (silica wafer). We have performed this study in order to check if the difference was due to the particular water/mica system or was characteristic of an evaporation process in the presence of a wetting surface. Our results show that the receding dynamic of alkane/silica system is in good agreement with the previously quoted theory. Experiments with pure water on same wafer (with hydrophilic treatment) have completed this study. A behavior close to water/mica system is observed, so the substrate's choice is not the origin of the problem. A theoretical analysis was also done considering phenomena like disjoining pressure at the mesoscopic scale. This allowed to widen the existing model in order to qualitatively describe the specific behavior of water on an hydrophilic substrate.

The second part deals with the coupling between spreading and nematic elasticity in the case of liquid crystal droplets. This nematic elasticity is due to the presence of an antagonist anchoring at liquid crystal interfaces. On hydrophilic substrates, the atmosphere humidity rate is a relevant parameter because it controls the instabilities appearing at the contact line. The macroscopic spreading laws appears very abnormal in comparison with the usual liquid one. On hydrophobic substrate, instabilities at the contact line were not observed. Therefore, the spreading laws are always abnormal. A theoretical analysis can now be performed with the results of this study.
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https://tel.archives-ouvertes.fr/tel-00011257
Contributor : Christophe Poulard <>
Submitted on : Thursday, December 22, 2005 - 12:30:43 PM
Last modification on : Monday, December 14, 2020 - 9:48:40 AM
Long-term archiving on: : Tuesday, April 6, 2010 - 4:32:47 PM

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  • HAL Id : tel-00011257, version 1

Citation

Christophe Poulard. Dynamiques de gouttelettes mouillantes. Analyse de données, Statistiques et Probabilités [physics.data-an]. Université Pierre et Marie Curie - Paris VI, 2005. Français. ⟨tel-00011257⟩

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