Paper Number
IR5 

Session
Interfacial Rheology

Title
Operation windows for interfacial rheometry

Presentation Date and Time
October 23, 2019 (Wednesday) 3:45

Track / Room
Track 7 / Room 306C

Authors (Click on name to view author profile)

  1. Renggli, Damian (ETH Zurich, Soft Materials)
  2. Ewoldt, Randy H. (University of Illinois at Urbana-Champaign, Department of Mechanical Science and Engineering)
  3. Vermant, Jan (ETH Zurich)

Author and Affiliation Lines (in printed abstract book)
Damian Renggli1, Randy H. Ewoldt2, and Jan Vermant1
1Soft Materials, ETH Zurich, Zurich, Switzerland; 2Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Speaker / Presenter 
Renggli, Damian

Text of Abstract
The interfacial rheology of liquid interfaces becomes complex if surface active species such as surfactants, particles or proteins are present at the interface. The broad interest in these complex interfaces covers topics from foam or emulsion stability to structural design in food or understanding the behavior of phospholipids as lung surfactants and is still an active area of research. Obtaining confident interfacial rheological data can be very challenging. Confining soft matter to a fluid interface leads to thin monolayers of material, therefore resulting in a very weak mechanical response which might be insufficient to be measured accurately. This inherently soft response combines with other important challenges, including instrument inertia, sample inertia (momentum diffusion), subphase flow (Boussinesq limits), contact line imperfections, and alignment errors. In this work, we study this list of experimental challenges and derive equations for the operating limits of various macroscopic rheometers including the interfacial needle shear rheometer, the double wall ring and the bi-cone geometries. We experimentally investigate the limitations defined intrinsically by the instrument as well as the ones emerging from the properties of the interface of interest. The results provide cautionary examples and guidelines for anyone measuring interfacial rheology with these techniques.