Paper Number
SF7 

Session
Surfactants, Foams and Emulsions

Title
Studying coalescence at different lengthscales: From films to droplets

Presentation Date and Time
October 11, 2022 (Tuesday) 9:50

Track / Room
Track 7 / Ontario

Authors (Click on name to view author profile)

  1. Chatzigiannakis, Emmanouil (Eindhoven University of Technology, Mechanical Engineering Department)
  2. Chen, Yun (University of Minnesota, Twin Cities, Mechanical Engineering)
  3. Bachnak, Rana B. (University of Minnesota - Twin Cities, Mechanical Engineering)
  4. Dutcher, Cari S. (University of Minnesota - Twin Cities, Mechanical Engineering & Chemical Engineering)
  5. Vermant, Jan (ETH Zürich, Materials)

Author and Affiliation Lines (in printed abstract book)
Emmanouil Chatzigiannakis1, Yun Chen2, Rana B. Bachnak2, Cari S. Dutcher3 and Jan Vermant4
1Mechanical Engineering Department, Eindhoven University of Technology, Eindhoven, The Netherlands; 2Mechanical Engineering, University of Minnesota - Twin Cities, Minneapolis, MN 55455; 3Mechanical Engineering & Chemical Engineering, University of Minnesota - Twin Cities, Minneapolis, MN 55431; 4Materials, ETH Zürich, Zürich, Switzerland

Speaker / Presenter 
Chatzigiannakis, Emmanouil

Keywords
experimental methods; emulsions; surfactants

Text of Abstract
The hydrodynamics of thin films is an important factor when it comes to the stability and rheology of multiphasic materials, such as foams, emulsions, and polymer blends. However, there have so far been only limited experimental studies addressing the dynamics of free standing thin films at conditions similar to those encountered at real applications. In this article we study a well-characterized system of a water-in-oil emulsions stabilized by a non-ionic surfactant (SPAN 80) close to its CMC. We employ a dynamic thin film balance, to study the dynamics of freestanding films under both constant and time-varied pressure drops. We compare with the recent results of Narayan et al. [Langmuir 36, 9827 (2020)] on colliding droplets of the same system with a hydrodynamic microfluidic trap, and show for the first time agreement between the two length-scales is possible, which indicates that the coalescence is indeed dominated by the dynamics in the film. We then address the scatter in the coalescence times and show that it can be affected by the presence of impurities, as well as by variations in the collision angle. Finally, we discuss the difficulties of extracting insight on the coalescence mechanism from coalescence time distributions when different effects such as impurities, small pressure variations, collision angle variations, and possible Marangoni-related instabilities are at play.