Paper Number
IR7 

Session
Interfacial Rheology

Title
Film drainage under spatiotemporally evolving surface stresses: A case study on beer foam

Presentation Date and Time
October 10, 2022 (Monday) 1:30

Track / Room
Track 5 / Sheraton 2

Authors (Click on name to view author profile)

  1. Chatzigiannakis, Emmanouil (Eindhoven University of Technology, Mechanical Engineering Department)
  2. Vermant, Jan (ETH Zürich, Materials)

Author and Affiliation Lines (in printed abstract book)
Emmanouil Chatzigiannakis1 and Jan Vermant2
1Mechanical Engineering Department, Eindhoven University of Technology, Eindhoven, The Netherlands; 2Materials, ETH Zürich, Zürich, Switzerland

Speaker / Presenter 
Vermant, Jan

Keywords
foams; food rheology; interfacial rheology

Text of Abstract
It is widely accepted that beer foam stability is controlled by the surface viscosity of the adsorbed layers that are predominantly proteinaceous. Using Double-Wall-Ring surface shear rheometry, tensiometry, and dynamic thin film balance measurements we show that in fact the physical mechanism responsible for foam stability depends on the type of beer. Although the traditional view of surface-viscosity controlled film stability is true for lager beers, Belgian ales are shown to exhibit negligible surface viscosities and are in contrast stabilized by Marangoni stresses. The strong recirculating Marangoni flows result in much higher film and foam lifetimes. Using beer as a starting point we generalize on the importance of surface stresses on film drainage. We show that when it comes to draining films with complex interfaces, surface stresses might change both in space as well as in time, in contrast to the generally assumed constant surface-stress boundary condition. This spatiotemporal evolution of surface stresses can have huge effects on film dynamics, and thus, on the stability and rheology of foams.