Paper Number
SC23 

Session
Suspensions and Colloids

Title
Cage formation and dynamics in repulsive and attractive glasses probed by high frequency rheology

Presentation Date and Time
October 11, 2022 (Tuesday) 10:50

Track / Room
Track 1 / Sheraton 4

Authors (Click on name to view author profile)

  1. Athanasiou, Thanasis (IESL-FORTH)
  2. Petekidis, George (IESL-FORTH)
  3. Mei, Baicheng (University of Illinois at Urbana-Champaign)
  4. Schweizer, Kenneth S. (University of Illinois at Urbana-Champaign)

Author and Affiliation Lines (in printed abstract book)
Thanasis Athanasiou1, George Petekidis1, Baicheng Mei2 and Kenneth S. Schweizer2
1IESL-FORTH, Heraklion, Greece; 2University of Illinois at Urbana-Champaign, Urbana, IL 61801

Speaker / Presenter 
Petekidis, George

Keywords
experimental methods; theoretical methods; colloids; glasses; suspensions

Text of Abstract
The cage idea has been widely utilized in colloidal suspensions as a central microscopic concept to describe a number of phenomena related with glassy dynamics. Here we probe the evolution of cage formation and shear elasticity in colloidal suspensions approaching and well inside the glass regime. Emphasis is given in the short-time dynamics utilizing linear viscoelastic (LVE) measurements by means of conventional rheometers and a home-made high frequency (HF) piezo-rheometer to probe the dynamic response in a broad range of volume fractions up to the very dense regime in proximity to RCP. We focus on the LVE spectra and on short times, where the caging effect is not so evident as the particles cannot fully explore their cage. This results to the virtual solid to liquid transition at elevated frequencies marked by the HF moduli crossover. On the other hand, caging becomes tighter as volume fraction increases and the in-cage rattling becomes more localized shifting the HF crossover to higher frequencies. The study of the dependence of the HF crossover properties (frequency and moduli) on volume fraction provides direct insights of the particle in-cage motion, and allows comparison with current theoretical models. We find that the above characteristic HF crossover properties exhibit two nearly exponential dependent volume fraction regimes. This experimentally robust finding is consistent with predictions of the microscopic nonlinear Langevin Equation dynamical theory with highly accurate structural input. We further explore the effect of attractive interactions either via the addition of linear polymer chain depletant or by inducing via slight refractive index mismatch van der Walls attraction. Particle localization is now determined by both entropic caging and enthalpic bonding, altering the high frequency viscoelastic response of the system.