Paper Number
IR7 

Session
Interfacial Rheology

Title
rheo-MAGIK: Investigating interfacial monolayers and their path dependent isotherms via combined neutron reflectivity and interfacial rheology technique

Presentation Date and Time
October 23, 2019 (Wednesday) 4:35

Track / Room
Track 7 / Room 306C

Authors (Click on name to view author profile)

  1. Tein, Ying-Heng S. (University of Delaware, Chemical and Biomolecular Engineering)
  2. Majkrzak, Charles F. (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)
  5. Wagner, Norman J. (University of Delaware, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Ying-Heng S. Tein1, Charles F. Majkrzak2, Brian Maranville2, Jan Vermant3, and Norman J. Wagner1
1Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716; 2Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD; 3ETH Zurich, Zurich, Switzerland

Speaker / Presenter 
Tein, Ying-Heng S.

Text of Abstract
Interfacial structure and rheological properties are critically important in biological (e.g. membranes) as well as many synthetic systems (e.g. emulsions), such that a better understanding how these are correlated can guide the formulation of systems with targeted interfacial properties. Mixed flow fields, typical of classical Langmuir trough experiments, convolute the interpretation of interfacial dilatational rheology for interfacial systems with both finite surface shear and dilatational moduli. Attempts have been made to resolve the anisotropic state of stress into their pure forms, either by multiple measurements in the Langmuir trough [1] or through the use of a radial trough [2]. In this presentation we describe the design and implementation of a new “Quadrotrough” to better approximate pure dilation or shear interface kinematics. The rheological capabilities of this interfacial trough are demonstrated through proof-of-concept experiments on widely studied, model systems. Importantly, this enables more clearly studying the path dependence of interfacial isotherms. Samples investigated include model steric acid insoluble monolayers as well as more complex macromolecules at the air-water interface. We critically test the hypothesis that anisotropic compression will only significantly affect the dilatational rheology for interfaces with finite surface shear moduli. This is important because convolution of mixed flow fields greatly complicates data interpretation. Combining the new Quadrotrough with both Brewster angle microscopy and neutron reflectivity provides detailed structural measurements of the interface at the microscale and nanoscale that elucidates the source of this path dependence. The potential for rheo-MAGIK, will be discussed and future investigations are reflected on for instrument development. References [1] Petkov, Jordan T., et al. Langmuir 16.8 (2000): 3703-3711. [2] Pepicelli, Martina, et al. Soft matter 13.35 (2017): 5977-5990.