Paper Number
GG41 

Session
Rheology of Gels, Glasses and Jammed Systems

Title
Tuning mechanical memory and aging in soft materials by oscillatory training

Presentation Date and Time
October 12, 2022 (Wednesday) 1:30

Track / Room
Track 3 / Sheraton 5

Authors (Click on name to view author profile)

  1. Edera, Paolo (ESPCI Paris - PSL, Molecular, Macromolecular Chemistry and Materials)
  2. Di Dio, Bruno F. (ESPCI Paris - PSL, Molecular, Macromolecular Chemistry and Materials)
  3. Aime, Stefano (Molecular, Macromolecular Chemistry, and Materials, ESPCI)
  4. Cloitre, Michel (ESPCI Paris - PSL, Molecular, Macromolecular Chemistry and Materials)

Author and Affiliation Lines (in printed abstract book)
Paolo Edera, Bruno F. Di Dio, Stefano Aime and Michel Cloitre
Molecular, Macromolecular Chemistry and Materials, ESPCI Paris - PSL, Paris, France

Speaker / Presenter 
Cloitre, Michel

Keywords
experimental methods; colloids; emulsions; foams; gels; glasses; jammed systems; polymer melts; polymer solutions; surfactants; suspensions

Text of Abstract
When soft materials solidify upon flow cessation, they store internal stresses at the origin of mechanical memory. Soft materials remember the last direction along which they have been sheared, which explains the spontaneous motion occurring without forced flow in colloidal glasses and biological materials [1]. They also exhibit physical aging responsible for slow evolution in the quiescent state. Directional memory and aging adversely affect the physical characterization of soft materials and are vital for process design. Preparing materials free of internal stresses is thus highly desirable.

Here we address this challenge for soft particle glasses (SPGs) made of deformable colloids jammed at high volume fraction. We show that driving SPGs periodically with a sequence of forced oscillations at constant stress amplitude erases the directional memory. The duration of oscillatory training controls aging. The applied stress has to be close to the point which marks the transition between reversible behavior and shear-induced dynamics [2].

To rationalize these results, we introduce a model based on the local stress distribution, P(σ), and its evolution during training. We associate the directional memory to the asymmetry of P(σ), which progressively decreases when the particles contributing to the tails of the distribution yield. Aging depends on the width of the distribution, which decreases when training becomes longer. It is thus possible to disentangle directional memory and aging. The effects of parameters like frequency, the stress amplitude, the number of cycles can be understood in this framework.

Our results offer a reliable and efficient way to determine of the transient dynamics of SPGs without directional memory. Preliminary results obtained for other types of yield stress materials support the generality of our method.

[1] L. Mohan, M. Cloitre, R. T. Bonnecaze, J. Rheol. 59, 63 (2015)
[2] L. Mohan, C. Pellet, M. Cloitre, R. T. Bonnecaze, J. Rheol. 57, 1023 (2013).