Paper Number
IR6 

Session
Interfacial Rheology

Title
Experimental and numerical analysis of the pendant drop experiment for complex interfaces

Presentation Date and Time
October 23, 2019 (Wednesday) 4:10

Track / Room
Track 7 / Room 306C

Authors (Click on name to view author profile)

  1. Jaensson, Nick O. (ETH Zurich, Department of Materials)
  2. Anderson, Patrick D. (Eindhoven University of Technology, Mechanical Engineering, Polymer Technology Group)
  3. Vermant, Jan (ETH Zurich)

Author and Affiliation Lines (in printed abstract book)
Nick O. Jaensson1, Patrick D. Anderson2, and Jan Vermant1
1Department of Materials, ETH Zurich, Zurich, Switzerland; 2Mechanical Engineering, Polymer Technology Group, Eindhoven University of Technology, Eindhoven, Noord-Brabant 5600 MB, The Netherlands

Speaker / Presenter 
Jaensson, Nick O.

Text of Abstract
Pendant drop experiments are frequently employed to obtain the interfacial or surface tension of liquid-liquid or liquid-gas interfaces. The general approach is to fit the Young-Laplace equation to a drop suspended from a capillary, which yields the surface tension and capillary pressure inside the drop. By performing oscillatory measurements, information about the adsorption/desorption of surface-active entities can be obtained. However, a crucial assumption when applying the Young-Laplace equation is that the interfacial tension is uniform and isotropic, which might not be true for structured, so-called “complex” interfaces. In these type of systems, the non-uniform deformation, combined with elastic properties of the interface, leads to extra and deviatoric surface stresses which are not necessarily uniform nor isotropic. Additionally, in-plane relaxation processes (i.e. viscoelasticity) might be mistaken for transport processes normal to the interface. Applying the Young-Laplace equation to such interfaces might lead to significant errors in the analysis, but is, unfortunately, standard practice. We present a combined experimental/numerical analysis of the pendant drop experiment for complex interfaces. Experiments are performed using carefully selected model interfaces. By estimating the surface stresses in the interface using a direct method, the validity of the Young- Laplace approach can be directly evaluated. For the numerical analysis, the finite element method is employed which solves the complete set of flow- and transport-equations and the interplay with complex interfacial rheology and/or transport processes toward or at the interface. By combining the experimental and numerical results, we delineate the regime where the Young-Laplace approach ceases to be valid, and other approaches for estimating the surface stress become necessary, and we demonstrate one such approach.