Paper Number
TM6 

Session
Rheometry: Advanced Techniques and Methods

Title
Gaining physical insights into LAOS experiments: Stress decomposition in LAOS of dense suspensions

Presentation Date and Time
October 21, 2019 (Monday) 1:30

Track / Room
Track 1 / Room 305A

Authors (Click on name to view author profile)

1. Ong, Edward Yong Xi (Cornell University, Applied Engineering and Physics)
2. Ramaswamy, Meera (Cornell University, Applied Engineering and Physics)
3. Cohen, Itai (Cornell University, Applied Engineering and Physics)

Author and Affiliation Lines (in printed abstract book)
Edward Yong Xi Ong, Meera Ramaswamy, and Itai Cohen
Applied Engineering and Physics, Cornell University, Ithaca, NY 14850

Speaker / Presenter 
Ong, Edward Yong Xi

Text of Abstract
Large amplitude oscillatory shear (LAOS) has emerged as the most used characterization methods for large, non-linear perturbation due to the ease of implementation and because it allows for independent probes of the time and length scales by tuning the frequency and amplitude of oscillation. The complex non-linear interactions that are the results of a LAOS experiment, however, are difficult to understand. Attempts to quantify LAOS behavior through techniques like Chebyshev polynomials and a Sequence of Physical Processes give insights into the shape of the LAOS curve and predicts thickening, thinning, stiffening and softening behaviors but provide limited understanding for the dynamics and interplay of the stresses involved. Here, we present an intuitive way of understanding the rich interactions present in the LAOS of shear-thickening suspensions by experimentally decomposing the stresses involved. The decomposition allows us to extract the hydrodynamic, contact and Brownian contributions across the Lissajous curve to map out the different stress dynamics across an oscillation cycle. Access to the time evolution of each stress component provides us with valuable insights on the potential microscopic details of the system, such as the time scales for the buildup and relaxation of the force chains during oscillation, the corresponding type of contact mechanism and the microstructure during the transition from low to high Péclet number and vice-versa. While we have chosen to demonstrate this experimental method on colloidal suspensions, the generality of the method also allows it to be used to investigate other non-linear systems such as gels and polymers.