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Dynamic Control of Evaporating Droplets Using a Point Source of Vapour

Malinowski, Robert Alexander; (2020) Dynamic Control of Evaporating Droplets Using a Point Source of Vapour. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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[thumbnail of A.1 A centered ethanol vapour source.avi] Video
A.1 A centered ethanol vapour source.avi - Supplemental Material

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[thumbnail of A.2 The Coffee Ring Effect.avi] Video
A.2 The Coffee Ring Effect.avi - Supplemental Material

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[thumbnail of A.3 Flattening of the central particle deposit by the droplet surface.avi] Video
A.3 Flattening of the central particle deposit by the droplet surface.avi - Supplemental Material

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[thumbnail of A.4 Lateral offset of an ethanol vapour source.avi] Video
A.4 Lateral offset of an ethanol vapour source.avi - Supplemental Material

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[thumbnail of A.5 Patterning “UCL” with an ethanol vapour source.avi] Video
A.5 Patterning “UCL” with an ethanol vapour source.avi - Supplemental Material

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[thumbnail of A.6 Attraction of a binary droplet to a water source.avi] Video
A.6 Attraction of a binary droplet to a water source.avi - Supplemental Material

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[thumbnail of A.7 Repulsion of a binary dropelt from a water source.avi] Video
A.7 Repulsion of a binary dropelt from a water source.avi - Supplemental Material

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[thumbnail of A.8 Linear deposition of poly(vinyl alcohol).avi] Video
A.8 Linear deposition of poly(vinyl alcohol).avi - Supplemental Material

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[thumbnail of A.9 Sinuous deposition of poly(vinyl alcohol).avi] Video
A.9 Sinuous deposition of poly(vinyl alcohol).avi - Supplemental Material

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[thumbnail of A.10 Patterning “ucl” from a poly(vinyl alcohol) droplet.avi] Video
A.10 Patterning “ucl” from a poly(vinyl alcohol) droplet.avi - Supplemental Material

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[thumbnail of A.11 Directing a phase change in a polyethylene glycol deposit.avi] Video
A.11 Directing a phase change in a polyethylene glycol deposit.avi - Supplemental Material

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[thumbnail of A.12  Mixing methyl red and bromothymol blue via combination of mobile droplets.avi] Video
A.12 Mixing methyl red and bromothymol blue via combination of mobile droplets.avi - Supplemental Material

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[thumbnail of A.13 Mixing HCl and NaOH via combination of pH indicating mobile droplets.avi] Video
A.13 Mixing HCl and NaOH via combination of pH indicating mobile droplets.avi - Supplemental Material

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Abstract

Over the past two decades, evaporating droplets have received growing attention owing to their ubiquity and hidden complexities. With inkjet printing becoming a more prominent manufacturing technique, due to its scalability and low cost, understanding and controlling droplet behaviour is becoming increasingly valuable. Here, a novel technique is presented, where a local vapour source is used to manipulate the local composition of an evaporating droplet's surface, either inducing surface tension driven flows, or influencing flows already present. In the former case, these flows can both guide material precisely within a droplet and control larger scale droplet phenomena, such as depinning. Ethanol vapours are shown to effectively combat the Coffee Ring Effect, a common hindrance in processes where a solid is deposited from a droplet, as well as provide additional control over deposition. Evaporating droplets of binary liquid mixtures can move freely over surfaces due to inherent surface tension gradients that form within them. Vapour sources are shown to influence and direct their motion. This new method of controlling motion is used to perform a variety of tasks, including deposition of material, with control over its position and morphology, and creating millimetre scale reactors with complex internal flows. The vapour sources used rely on a small amount of solvent, so have minimal impact on droplets beyond the induced flows. The technique is also simple, meaning it easily accessible for further research, and for scaling to manufacturing processes.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Dynamic Control of Evaporating Droplets Using a Point Source of Vapour
Event: UCL
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
Keywords: Droplet, Evaporation, Deposition, Printing
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/10096952
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