Paper Number
SF1
Session
Surfactants, Foams, and Emulsions
Title
Mimicking coalescence using a dynamic thin film balance technique
Presentation Date and Time
October 21, 2019 (Monday) 9:50
Track / Room
Track 5 / Room 306A
Authors
- Chatzigiannakis, Emmanouil (ETH Zurich, Materials Department)
- Vermant, Jan (ETH Zurich)
Author and Affiliation Lines
Emmanouil Chatzigiannakis and Jan Vermant
Materials Department, ETH Zurich, Zürich CH-8093, Switzerland
Speaker / Presenter
Chatzigiannakis, Emmanouil
Text of Abstract
Thin liquid film (TLF) dynamics is considered to be an important (if not deciding) factor when it comes to foam and emulsion stability. When two bubbles/droplets come into close proximity a TLF is usually formed between them, which gradually drains until it ruptures. The role of the interfacial properties on the hydrodynamic drainage process of various systems under a constant driving force has received some attention [1,2]. However, there are no experimental studies regarding how the rheological properties of the bulk liquid (e.g. viscoelasticity, shear thinning) affect the overall drainage process, especially under dynamic pressure conditions. Such experiments will provide significant information related to flow-induced coalescence processes, as well as to the behavior of foams and emulsions under oscillatory shear. In this study, the drainage dynamics of liquid-air films of polymer solutions were examined using a variation of the thin film balance technique which allows us to vary the Capillary number [3]. A standard thin film balance was modified to perform hydrodynamic studies. Constant, as well as dynamic pressure was applied in order to mimick both head-on and glancing collisions. The effect of three parameters on drainage was studied, namely that of driving force, polymer concentration and molecular weight. All parameters were found to influence non-trivially the drainage of the thin liquid films, giving rise to a multitude of phenomena, both with respect to flow instabilities (symmetric-to-asymmetric drainage transitions, cyclic dimpling and vortices), as well as with respect to confinement effects on structure and possibly rheology. References: [1] Hermans, E. et al. (2015), Soft Matter, 11(41): 8048. [2] Kannan, A. et al. (2018), Langmuir, 34(2): 630. [3] Beltramo, P.J. et al. (2016), Soft Matter, 12(19): 4324.