Henrich, Franziska Monika (2018)
Dynamic dewetting of surfactant solutions.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung
Kurzbeschreibung (Abstract)
Wetting and dewetting play a significant role in many natural processes as well as in many technical applications like in printing or cleaning procedures. To optimize these kind of processes the understanding of the dewetting behaviour of surfactant solutions is important. Previous investigations showed, that an addition of surfactant to a solution changes the dewetting behaviour. Those studies revealed, that the dewetting behaviour is depending on the surfactant concentration, even if the concentration is below the critical micelle concentration (CMC). Nevertheless the effects due to the presence of surfactants are not well understood. Therefore, I investigated in this work, how surfactants influence the dewetting behaviour on smooth and structured surfaces. The dewetting behaviour of various surfactant solutions (non-ionic, cationic and anionic) on a smooth polystyrene surface were compared at different concentrations well below the CMC. All surfactants show the same tendency, independent of their charge: the higher the surfactant concentration, the lower the receding contact angle as well as the film formation velocity. Scaling with the CMC leads almost to a master curve. The change in contact angle can be interpreted by local surface gradients, e.g. Marangoni stresses. At velocities > 10 mm/s the experimental results can be described by the hydrodynamic theory. Additionally to the wetting behaviour on smooth surfaces, the influence of a structured surface in the presence of surfactant was studied. A custom made printing plate with different structured areas was used as model surface. The dewetting behaviour is comparable to dewetting on smooth surfaces, the higher the surfactant concentration the lower the contact angle as well as the critical film formation velocity. The influence of the structured surface decreases with increasing concentration. The decreasing influence of the structured surface is due to the fact, that with increasing concentration the Marangoni stress towards the three phase contact line increases. These Marangoni stresses dominate the stress due to pinning on the structured surface. Since a direct measurement of the Marangoni stresses is not easily possible, I measured instead the flow profile on a microscopic lenght scale close to the contact line. A newly developed setup is able to image of a moving contact line over a long time period. The measurement of the flow profile showed that at a distance smaller than 30 μm the flow from surfactant solution differs from the one of pure water. This is in agreement with the model of the Marangoni force towards the contact line, which results in the decrease of the contact angle macroscopically.
| Typ des Eintrags: | Dissertation | ||||
|---|---|---|---|---|---|
| Erschienen: | 2018 | ||||
| Autor(en): | Henrich, Franziska Monika | ||||
| Art des Eintrags: | Erstveröffentlichung | ||||
| Titel: | Dynamic dewetting of surfactant solutions | ||||
| Sprache: | Englisch | ||||
| Referenten: | Hardt, Prof. Dr. Steffen ; Butt, Prof. Dr. Hans-Jürgen | ||||
| Publikationsjahr: | 2018 | ||||
| Ort: | Darmstadt | ||||
| Datum der mündlichen Prüfung: | 27 Juni 2017 | ||||
| URL / URN: | http://tuprints.ulb.tu-darmstadt.de/6894 | ||||
| Kurzbeschreibung (Abstract): | Wetting and dewetting play a significant role in many natural processes as well as in many technical applications like in printing or cleaning procedures. To optimize these kind of processes the understanding of the dewetting behaviour of surfactant solutions is important. Previous investigations showed, that an addition of surfactant to a solution changes the dewetting behaviour. Those studies revealed, that the dewetting behaviour is depending on the surfactant concentration, even if the concentration is below the critical micelle concentration (CMC). Nevertheless the effects due to the presence of surfactants are not well understood. Therefore, I investigated in this work, how surfactants influence the dewetting behaviour on smooth and structured surfaces. The dewetting behaviour of various surfactant solutions (non-ionic, cationic and anionic) on a smooth polystyrene surface were compared at different concentrations well below the CMC. All surfactants show the same tendency, independent of their charge: the higher the surfactant concentration, the lower the receding contact angle as well as the film formation velocity. Scaling with the CMC leads almost to a master curve. The change in contact angle can be interpreted by local surface gradients, e.g. Marangoni stresses. At velocities > 10 mm/s the experimental results can be described by the hydrodynamic theory. Additionally to the wetting behaviour on smooth surfaces, the influence of a structured surface in the presence of surfactant was studied. A custom made printing plate with different structured areas was used as model surface. The dewetting behaviour is comparable to dewetting on smooth surfaces, the higher the surfactant concentration the lower the contact angle as well as the critical film formation velocity. The influence of the structured surface decreases with increasing concentration. The decreasing influence of the structured surface is due to the fact, that with increasing concentration the Marangoni stress towards the three phase contact line increases. These Marangoni stresses dominate the stress due to pinning on the structured surface. Since a direct measurement of the Marangoni stresses is not easily possible, I measured instead the flow profile on a microscopic lenght scale close to the contact line. A newly developed setup is able to image of a moving contact line over a long time period. The measurement of the flow profile showed that at a distance smaller than 30 μm the flow from surfactant solution differs from the one of pure water. This is in agreement with the model of the Marangoni force towards the contact line, which results in the decrease of the contact angle macroscopically. |
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| URN: | urn:nbn:de:tuda-tuprints-68943 | ||||
| Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 500 Naturwissenschaften und Mathematik > 500 Naturwissenschaften 500 Naturwissenschaften und Mathematik > 530 Physik 500 Naturwissenschaften und Mathematik > 540 Chemie 600 Technik, Medizin, angewandte Wissenschaften > 600 Technik 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau |
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| Fachbereich(e)/-gebiet(e): | 16 Fachbereich Maschinenbau 16 Fachbereich Maschinenbau > Fachgebiet Nano- und Mikrofluidik (NMF) 16 Fachbereich Maschinenbau > Fachgebiet Nano- und Mikrofluidik (NMF) > Wetting Phenomena |
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| Hinterlegungsdatum: | 13 Mai 2018 19:55 | ||||
| Letzte Änderung: | 13 Mai 2018 19:55 | ||||
| PPN: | |||||
| Referenten: | Hardt, Prof. Dr. Steffen ; Butt, Prof. Dr. Hans-Jürgen | ||||
| Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 27 Juni 2017 | ||||
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