Paper Number
ET21 

Session
Advanced Experimental Techniques/Methods in Rheology

Title
Computing the linear viscoelastic properties of soft gels using an Optimally Windowed Chirp protocol

Presentation Date and Time
October 17, 2018 (Wednesday) 2:20

Track / Room
Track 5 / San Felipe Room

Authors (Click on name to view author profile)

  1. Bouzid, Mehdi (Universite Paris Sud, LPTMS)
  2. Keshavarz, Bavand (Massachusetts Institute of Technology, Mechanical Engineering)
  3. Geri, Michela (MIT, Mechanical Engineering)
  4. Divoux, Thibaut (CNRS Bordeaux, CNRS-MIT, MSE2)
  5. Del Gado, Emanuela (Georgetown University)
  6. McKinley, Gareth H. (Massachusetts Institute of Technology)

Author and Affiliation Lines (in printed abstract book)
Mehdi Bouzid1, Bavand Keshavarz2, Michela Geri2, Thibaut Divoux3, Emanuela Del Gado4, and Gareth H. McKinley2
1LPTMS, Universite Paris Sud, Paris, France; 2Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; 3MSE2, CNRS Bordeaux, CNRS-MIT, Cambridge, MA; 4Georgetown University, Washington, DC

Speaker / Presenter 
Del Gado, Emanuela

Text of Abstract
We use molecular dynamics simulations of a model three-dimensional particulate gel, to investigate the linear viscoelastic response. The numerical simulations are combined with a novel test protocol (the optimally-windowed chirp or OWCh), in which a continuous exponentially-varying frequency sweep windowed by a tapered cosine function is applied. The mechanical response of the gel is then analyzed in the Fourier domain. We show that i) OWCh leads to an accurate computation of the full frequency spectrum at a rate significantly faster than with the traditional discrete frequency sweeps, and with a reasonably high signal-to-noise ratio, and ii) the bulk viscoelastic response of the microscopic model can be described in terms of a simple mesoscopic constitutive model. The simulated gel response is in fact well described by a mechanical model corresponding to a fractional Kelvin-Voigt model with a single Scott-Blair (or springpot) element and a spring in parallel. By varying the viscous damping and the particle mass used in the microscopic simulations over a wide range of values, we demonstrate the existence of a single master curve for the frequency dependence of the viscoelastic response of the gel that is fully predicted by the constitutive model. By developing a fast and robust protocol for evaluating the linear viscoelastic spectrum of these soft solids, we open the path towards novel multiscale insight into the rheological response for such complex materials.