Paper Number
AT1 

Session
Advanced Techniques and Methods

Title
Frequency-sweep MAOS: Faster and cheaper medium-amplitude oscillatory shear

Presentation Date and Time
February 15, 2017 (Wednesday) 1:30

Track / Room
Track 4 / Sandhill Crane

Authors (Click on name to view author profile)

1. Singh, Piyush K. (University of Illinois at Urbana-Champaign, Mechanical Science and Engineering)
2. Soulages, Johannes M. (ExxonMobil Research and Engineering, Corporate Strategic Research)
3. Ewoldt, Randy H. (University of Illinois at Urbana-Champaign, Mechanical Science and Engineering)

Author and Affiliation Lines (in printed abstract book)
Piyush K. Singh¹, Johannes M. Soulages², and Randy H. Ewoldt^1
1Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801; ²Corporate Strategic Research, ExxonMobil Research and Engineering, Annandale, NJ 08801

Speaker / Presenter 
Singh, Piyush K.

Text of Abstract
Medium-amplitude oscillatory shear (MAOS) is asymptotically-nonlinear and a valuable tool for inferring structure from rheology. However, a drawback of conventional MAOS is the time and material intensive nature of experiments. Many strain amplitude sweeps, and typically multiple sample loadings, are required to obtain frequency-dependent properties. Here, we propose a new MAOS methodology that is faster (fewer data points) and cheaper (fewer material loadings): the frequency-sweep MAOS. Similar to conventional small amplitude oscillatory shear (SAOS), we use only a frequency-sweep at a suitable strain amplitude. A key challenge is that measurable MAOS data lives between the instrument resolution (at small strains) and strongly nonlinear behavior beyond asymptotic nonlinearity (at large strains). We propose criteria to validate MAOS data taken at a single strain amplitude, and additionally provide quantitative estimates of the measurement uncertainty. Full characterization of all four MAOS measures requires two frequency sweeps: one frequency sweep for the third-harmonic measures and two frequency sweeps (at different input strain amplitudes) for the first-harmonic measures. The proposed method is validated for a linear polyethylene melt. This new, faster, and material economical MAOS approach will be beneficial for precious samples such as model branched polymers which are typically available in very limited quantities. Additionally, the lessons learned are extended to frequency-sweep SAOS for generating confidence that the measures are indeed in the linear regime.