Paper Number
RI1 

Session
Rheology and Mobility at Interfaces

Title
Shear and dilation rheology of complex fluid interfaces

Presentation Date and Time
October 12, 2021 (Tuesday) 3:45

Track / Room
Track 6 / Ballroom 1

Authors (Click on name to view author profile)

  1. Tein, Y. Summer (University of Delaware, Center for Neutron Science)
  2. Majkrzak, Charles (National Institute of Standards and Technology, Center for Neutron Research)
  3. Maranville, Brian (National Institute of Standards and Technology, Center for Neutron Research)
  4. Vermant, Jan (ETH Zurich, Materials Departement)
  5. Thompson, Benjamin (University of Delaware, Center for Neutron Science)
  6. Wagner, Norman J. (University of Delaware, Chemical & Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Y. Summer Tein1, Charles Majkrzak2, Brian Maranville2, Jan Vermant3, Benjamin Thompson1 and Norman J. Wagner1
1Chemical & Biomolecular Engineering, University of Delaware, Newark, DE 19716; 2Center for Neutron Research, National Institute of Standards and Technology, gaithersburg, MD; 3Materials Departement, ETH Zurich, Zurich 8093, Switzerland

Speaker / Presenter 
Wagner, Norman J.

Keywords
experimental methods; biological materials; emulsions; gels; interfacial rheology; rheology methods; surfactants

Text of Abstract
Interfacial structure and rheological properties are critical for function in natural and biological systems (e.g. lung surfactants, membranes) as well as many consumer products and industrial processes (e.g., foams, emulsions). As interfaces are often rheologically complex, the goal of this research is to develop instrumentation to accurately measure mechanical properties of complex interfaces that depend on time and deformation-history, e.g., interfaces with viscoelasticity and thixotropy. Mixed flow fields typical of classical Langmuir troughs convolute interfacial dilation with shear, often creating an interface out of equilibrium. Consequently, attempts have been made to deconvolute the interfacial stress by multiple measurement protocols in Langmuir trough experiments[1]. Alternatively, a purely radial deformation is used to determine the instantaneous dilation modulus in a radial trough [2]. However, complex interfaces may be far from equilibrium upon compression with exceptionally long relaxation times. To address these needs, we present a new interfacial trough designed to apply well-defined shear and dilation deformation histories with well-defined interface kinematics. Interfacial kinematics are validated with PIV and meso and nanoscale structure are measured in situ with BAM and neutron reflectivity. The rheological capabilities of this new interfacial trough are demonstrated through experiments on stearic acid at the air-water interface and in the presence of salts in the subphase, leading to an interfacial gel as a complex, shear-history dependent material. Further, the effects of compression and shear annealing of complex interfaces at the air-water interface are demonstrated on microgels, polymers, lipids and biopolymers. The further development of an instrument suitable for use on neutron and x-ray beamlines as well as individual laboratories will be described. [1] Petkov, Jordan T., et al. Langmuir?16.8 (2000): 3703-3711. [2] Pepicelli, Martina, et al. Soft matter?13.35 (2017): 5977-5990