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Mass Transfer and Spontaneous Emulsification in Ternary Mixtures

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Mass Transfer and Spontaneous Emulsification in Ternary Mixtures University Degree in Industrial Technologies 2018-2019 Bachelor Thesis Mass Transfer and Spontaneous Emulsification in Ternary Mixtures Miguel Zürcher Guinea Oscar R. Enríquez Paz y Puente 23rd of September 2019 This work is licensed under Creative Commons Attribution – Non Commercial – Non Derivatives SUMMARY The combination of miscible and immiscible liquids in ternary mixtures can cause a va- riety of interesting physical phenomena. A common example of these three component mixtures is found when having anise oil based liquors found in most countries around the Mediterranean. Raki, from Turkey, Pastis from France, or Ouzo in Greece all seem to magically turn into a milky white colour when adding water. The addition of water makes alcohol mix with it, causing the oil, immiscible in water, to supersaturate and nucleate. This spontaneous emulsification of oil in water makes the light scatter causing its white colour. This is called the Ouzo effect after the traditional Greek drink. Although humans have interacted with the Ouzo effect for centuries, it was not until 2003 when the physics behind were studied in depth by Vitale and Katz. Since then more sci- entists have taken on this topic, especially as numerous applications of the Ouzo effect in industry have arisen, mainly in the biotechnology and nano-technology fields. However, today there is still a great lack of knowledge on the mechanisms that play a role in the Ouzo effect. Studies of drops in Ouzo systems have proven to involve a large amount of complex flows and interfacial phenomena as well as the spontaneous emulsification of oil inside the drop. Gradients in concentration and surface tension cause Marangoni stresses making the drop shake, and diffusion processes to take place. The mass transfer, buoyancy flows, capillary forces, and the interface dynamics together with the Ouzo effect make a very interesting system to be explored. This project summarises the known physics involved behind the Ouzo effect and multi- component drops, as well as their multiple applications in modern day industry. It contin- ues the work on studying the fate of water drops in different compositions of oil/alcohol mixtures. The densities of ethanol/water mixtures are known and are documented in numerous pa- pers. However densities of anethole and ethanol have never been quantified. The densi- ties of different anethole/ethanol compositions have been measured. These values have then been fitted to the Jouyban-Acree model. This model extrapolates our experimental measurement to be able to estimate very precisely the density of any composition of our mixture. An experiment was designed and setup up to explore different aspects of dissolving multi- component drops. Through this experiment we could observe different phenomena previ- ously mentioned, especially the rate at which diffusion took place. The experiment was analysed through digital image processing, and different geometrical magnitudes of the drop were tracked such as the surface are or the volume. The bond number was also tracked by means of the pendant drop fitting technique. These results were compared between both compositions and with estimated theoretical values. iii Keywords: Ouzo, Marangoni, Drop, Anethole, Ethanol, Water, Pendant, Bond. iv DEDICATION Firstly, I would like to thank my mentor for this project Oscar Enríquez, for putting forward this idea for my project. I am very grateful to have had him guiding me through- out the whole project and helping me in everything he could. Secondly, I would like to thank Jose and Nacho, for making the countless hours in the lab together fun and for lending me a hand when needed. I would also like to thank the laboratory technicians, and the rest of the professors in the fluids department, for gladly responding to any doubts I may have had. Lastly, I would like to thank all my friends and family for their support and encourage- ment in everything I set out to do. v CONTENTS 1. INTRODUCTION....................................1 2. STATE OF THE ART..................................2 2.1. Small Scale Physics.................................2 2.2. The Ouzo Effect...................................5 2.3. Ouzo Drops...................................... 11 2.4. Applications..................................... 14 3. ANETHOLE-ETHANOL DENSITY CHARACTERISATION........... 16 3.1. Realisation of the Experiment............................ 16 3.2. Results and Conclusions............................... 18 3.3. Future Ideas...................................... 20 4. PENDANT DROP EXPERIMENT.......................... 21 4.1. Realisation of the Experiment............................ 21 4.2. Recording of the Experiment............................ 22 4.3. Analysis of the experiment (image processing with MATLAB)......... 23 4.3.1. Geometry of the Drop.............................. 25 4.3.2. Bond Number of the drop............................ 27 4.4. Results and Conclusions............................... 32 4.5. Future Ideas...................................... 37 5. CONCLUSIONS.................................... 38 BIBLIOGRAPHY...................................... 39 APPENDICES....................................... 41 A. TABLES OF THE JOUYBAN-ACREE MODELS.................. B. EXTRA GRAPHS OBTAINED FROM THE PENDANT DROP EXPERIMENT. vii LIST OF FIGURES 2.1 Tears of wine caused by the Marangoni effect................3 2.2 The different mechanisms that can cause emulsion degradation.......4 2.3 Otswald ripening mechanism........................5 2.4 The Ouzo effect. 1-2 Ouzo with no added water. 3-4 Emulsification of the drink after the addition of water.....................6 2.5 Ternary Diagram of the "ouzo mixture"...................7 2.6 Droplet diameter as a function of excess oil for different compositions...8 2.7 Droplet diameters at 25oC and 50oC.....................9 2.8 Plot of the volume of the dispersion in a function of time at different concentration of anethol for (a) 5%-95% ethanol/water mixture and (b) 30%-70% ethanol/water mixture....................... 10 2.9 Estimated surface tension of the drops as a function of ethanol concen- tration. Of ethanol/water mixtures of 5%-95% (Squares), 10%-90% (Cir- cles), 20%-80% (Triangle pointing upwards), 30%-70% (Triangle point- ing downwards)............................... 10 2.10 Plot of drop Radius as a function of time (Black dots, left axis) and the scattering intensity (white dots, right axis)................. 11 2.11 The four stages of an evaporating Ouzo drop on a hydrophobic surface.. 12 2.12 The different flows in a dissolving water/ethanol drop in anethole..... 13 2.13 Frame from the award winning video "The shaky life of a water drop in an anise oil-rich environment"....................... 14 3.1 Krüss Force Tensiometer-K20....................... 17 3.2 Set for determining density of liquids................... 17 3.3 Experimental and Jouyban-Acree Model values for anethole/ethanol bi- nary mixtures at 24oC............................ 19 3.4 Densities of Ethanol/Anethole and Ethanol/Water mixtures for different concentration of Ethanol........................... 20 4.1 Experiment setup. Close up of the pendant drop on the right........ 21 4.2 Experiment setup............................... 22 ix 4.3 Ultrasonic cleaner (right), Tray two hold the objects to be cleaned (left). 23 4.4 Original image. Dotted lines refer to the limits of the capillary. The rectangle represents the area which the software will crop to work on... 24 4.5 Subtraction of the background (middle) from the original image (left), to make most of the background black in the new image (right)........ 24 4.6 Results of the segmentation process steps 2-7................ 25 4.7 The detected contour of this frame...................... 26 4.8 How a disc of a row in the drop would look like. The width of the disc is not to scale in this image........................... 26 4.9 Geometrical variables involved in the calculation of the Bond number... 28 4.10 Schematic of the pendant drop tensiometry process............. 29 4.11 Flow diagran of the fitting process for frame k............... 30 4.12 Result of the fitting Bond Process...................... 31 4.13 Example of how a circle is fitted to the apex of the drop toknow R0.... 32 4.14 Frame from an experiment with 4:1 in composition............. 33 4.15 Results of the volume growth of the 4 experiments analyse in 4:1 mixture until detachment............................... 33 4.16 Results of the volume growth of the 4 experiments analyse in 3:1 mixture until detachment............................... 34 4.17 Results of the volume growth of the drop in both compositions until de- tachment................................... 35 4.18 Bond numbers as the drop grows....................... 36 4.19 Bond numbers of both compositions 3:1 and 4:1.............. 36 4.20 Experimental setup of synthetic Schlieren.................. 37 B.1 Evolution of the drop surface area, since the moment the capillary is in- serted in the 4:1 Anethole/Ethanol mixture................. B.2 Evolution of the drop surface area, since the moment the capillary is in- serted in the 3:1 Anethole/Ethanol mixture................. B.3 Evolution of the drop volume, since the moment the capillary is inserted in the 4:1 Anethole/Ethanol mixture..................... B.4 Evolution of the drop volume, since the moment the capillary is inserted in the 3:1 Anethole/Ethanol mixture..................... x B.5 Evolution of the drop volume, since the moment the drop reaches
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