Paper Number
RS12 

Session
Techniques and Methods: Rheometry & Spectroscopy/Microscopy

Title
New metrics to quantify the brittle-like behavior of yield-stress fluids in extension

Presentation Date and Time
October 11, 2022 (Tuesday) 3:45

Track / Room
Track 6 / Mayfair

Authors (Click on name to view author profile)

  1. Fernandes, Rubens R. (University of Illinois Urbana-Champaign, Department of Mechanical Science and Engineering)
  2. Boehm, Michael W. (Motif FoodWorks, Inc.)
  3. Baier, Stefan K. (Motif FoodWorks, Inc.)
  4. Ewoldt, Randy H. (University of Illinois at Urbana-Champaign, Mechanical Science and Engineering)

Author and Affiliation Lines (in printed abstract book)
Rubens R. Fernandes1, Michael W. Boehm2, Stefan K. Baier2 and Randy H. Ewoldt1
1Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign, Urbana, IL 61801; 2Motif FoodWorks, Inc., Boston, MA

Speaker / Presenter 
Fernandes, Rubens R.

Keywords
experimental methods; consumer products; emulsions; foams; food rheology; gels; glasses; jammed systems; pharmaceuticals; rheometry techniques; suspensions

Text of Abstract
In this work, we introduce and study new metrics to quantitatively describe the brittle-like behavior of yield stress fluids in uniaxial extension. Soft materials can fracture in distinct ways in extensional experiments, but this cannot be reliably predicted from shear properties and no quantitative metrics exist to describe and compare this important behavior. Brittle-like yielding in extension is characterized by sudden break-up and fracture, leaving behind rough and irregular surfaces, whereas ductile-like yielding is associated with necking and pinch-off, leading to a conical break-up profile. We experimentally test a wide range of yield-stress fluids, such as model materials, consumer goods, food spreads, and cosmetic products in uniaxial extension and classify the response according to human visual perception of failure type. We then examine several different metrics to quantify geometric features of sample silhouettes after extensional break-up, in addition to features of force-extension curves, to evaluate brittleness. Metrics based on machine vision of the fractured samples, such as the total harmonic distortion obtained from a spectral analysis of the silhouettes, reproduce the supervised categorization. Our results demonstrate the importance of reporting photographs of materials after rheometric experiments, and of quantifying this visualization to more fully describe the response of complex yield-stress fluids and their brittleness in extension.