Paper Number
AP1
Session
Award Presentations
Title
Memory effects in colloidal gels
Presentation Date and Time
October 18, 2018 (Thursday) 8:00
Track / Room
Award Presentations / Galleria I
Authors
- Divoux, Thibaut (CNRS Bordeaux, CNRS-MIT, MSE2)
Author and Affiliation Lines
Thibaut Divoux
MSE2, CNRS Bordeaux, CNRS-MIT, Cambridge, MA
Speaker / Presenter
Divoux, Thibaut
Text of Abstract
Gelation of colloidal suspensions plays a crucial role in the formation of numerous materials. Examples range from cement to yogurt, which result respectively from the aggregation of CSH nanoparticles and casein micelles. In both systems, short-range attractive interactions between particles lead to the formation of a percolated network that is responsible for the solid-like behavior of the material at rest. Generated by a kinetic arrest, these solids are metastable out-of-equilibrium structures, whose properties are sensitive to the route followed during gelation. In that context, external shear often comes to compete with the attractive interactions that drives the gelation, affecting the gel microstructure, which encodes the shear history. In this talk, I will discuss various aspects of shear-induced memory effect in colloidal gels. First, I will illustrate a way to quantify the gel’s memory through the so called rheological hysteresis. Indeed, the constitutive equation of colloidal gels, i.e. shear stress versus shear rate, is generally obtained by sweeping up or down the shear rate over a finite temporal window. In general, the up and down sweeps do not superimpose and define a rheological hysteresis loop, which can be used to define a single timescale characteristic of the gel. Second, limiting the previous protocol to a single down sweep that brings the gel from a fluidized state to a complete stop, I will show that flow cessation can be used to tune the structural and mechanical properties of gels. Indeed, rheo-electric measurements reveal that abrupt flow cessation leads to strong and connected gels, whereas slow ramps lead to softer and less-conductive gels, a signature of lower connectivity in the sample-spanning network. This scenario is robust and data obtained with various flow cessation protocols and different particle concentrations collapse on a master curve that could be useful for the design of colloidal-based materials.