Paper Number
GG32 

Session
Rheology of Gels, Glasses and Jammed Systems

Title
The unexpectedly slow gelation dynamics of cellulose nanocrystals

Presentation Date and Time
October 11, 2022 (Tuesday) 4:45

Track / Room
Track 3 / Sheraton 5

Authors (Click on name to view author profile)

  1. Morlet-Decarnin, Lise (ENSL, CNRS, Laboratoire de Physique)
  2. Divoux, Thibaut (ENSL, CNRS, Laboratoire de physique)
  3. Manneville, Sébastien (ENSL, CNRS, Laboratoire de physique)

Author and Affiliation Lines (in printed abstract book)
Lise Morlet-Decarnin, Thibaut Divoux and Sébastien Manneville
Laboratoire de Physique, ENSL, CNRS, Lyon, France

Speaker / Presenter 
Morlet-Decarnin, Lise

Keywords
colloids; gels; glasses; suspensions

Text of Abstract

Cellulose nanocrystals (CNCs) are rodlike biosourced colloidal particles used as key building blocks in a growing number of materials with innovative mechanical or optical properties. While CNCs form stable suspensions at low volume fractions in pure water, they aggregate in the presence of salt and form colloidal gels with time-dependent properties.

Here, we study the impact of salt concentration on the slow aging dynamics of CNC gels following the cessation of a high-shear flow that fully fluidizes the sample. We show that the higher the salt content, the faster the recovery of elasticity upon flow cessation. Most remarkably, the elastic modulus G' obeys a time-composition superposition principle: the temporal evolution of G' can be rescaled onto a universal sigmoidal master curve spanning 13 orders of magnitude in time for a wide range of salt concentrations. Such a rescaling is obtained through a time-shift factor that follows a steep power-law decay with increasing salt concentration, until it saturates at large salt content. These findings are robust to changes in the type of salt and in the CNC content.

Furthermore, time-resolved measurements of the viscoelastic spectra during recovery show that the characteristic time scale t* that corresponds to the inflexion point of the sigmoidal master curve also corresponds to the true gelation time of the CNC dispersion. Interestingly, the timescale t* is two orders of magnitude larger than the elastic and loss modulus crossing time tc measured at 1Hz. These results suggest that the gel recovery first involves slow glassy-like dynamics due to the steric hindrance of the anisotropic CNC nanoparticles, followed by their percolation into a gel-like network.