[Paper Review] How colloidal suspensions that age are rejuvenated by strain application

Virgile Viasnoff, Stéphane Jurine+1 more|arXiv (Cornell University)|Oct 29, 2002

Material Dynamics and Properties3 citations

TL;DR

This study demonstrates that oscillatory strain can both rejuvenate and overage dense colloidal suspensions, depending on strain amplitude and duration. Using multispeckle diffusing wave spectroscopy, the authors show that high strain erases memory (rejuvenation), while moderate strain accelerates aging (overaging), with the Soft Glassy Rheology model explaining the dual behavior via a bimodal relaxation time distribution.

ABSTRACT

We present here a microscopic study of the effect of shear on a dense purely repulsive colloidal suspension. We use Multispeckle Diffusing Wave Spectroscopy to monitor the transient motions of colloidal particles after being submitted to an oscillatory strain. This technique proves efficient to record the time evolution of the relaxation times distribution. After a high oscillatory shear, we show that this distribution displays a full aging behavior. Oppositely, when a moderate shear is applied the distribution is modified in a non trivial way. Whereas high shear is able to erase all the sample history and rejuvenate it, a moderate shear helps it to age. We call this phenomena overaging. We demonstrate that overaging can be understood if the complete shape of the relaxation time distribution is taken into account. We finally report how the Soft Glassy Rheology model accounts for this effect.

Motivation & Objective

• To investigate the microscopic effects of oscillatory strain on the dynamic relaxation of aging colloidal suspensions.
• To determine whether strain can erase or accelerate aging in glassy colloidal systems.
• To reconcile experimental observations of non-monotonic relaxation dynamics with the Soft Glassy Rheology (SGR) model.
• To analyze how the full distribution of relaxation times governs the system's response to mechanical perturbations.

Proposed method

• Employed multispeckle diffusing wave spectroscopy (MSDWS) to monitor transient particle motions after strain application.
• Applied oscillatory strain histories with varying amplitudes (γ₀) and durations (du) to probe memory effects.
• Measured time evolution of the relaxation time distribution P(ε) to detect aging, rejuvenation, or overaging.
• Used the Soft Glassy Rheology (SGR) model with energy-dependent escape rates Γ_out(E) and entry rates Γ_in(E) to simulate strain effects.
• Modeled strain effects as a multiplicative factor exp[(1/2)kl²/x] on the escape rate, modifying the energy landscape.
• Incorporated strain-dependent elastic modulus k = k₀ + κE to assess the impact on rejuvenation completeness.

Experimental results

Research questions

• RQ1 How does oscillatory strain affect the relaxation time distribution in aging colloidal suspensions?
• RQ2 Can strain both rejuvenate and overage a system, and under what conditions does each dominate?
• RQ3 To what extent can the Soft Glassy Rheology model quantitatively explain the observed dual behavior?
• RQ4 What role does the complete shape of the relaxation time distribution play in determining macroscopic response?
• RQ5 Is complete rejuvenation possible under realistic strain histories, and what conditions enable it?

Key findings

• High oscillatory strain fully erases the system's history, leading to complete rejuvenation by resetting the relaxation time distribution.
• Moderate strain induces overaging, where the relaxation time distribution shifts toward longer times due to accelerated aging.
• The relaxation time distribution develops a bimodal structure after strain: one peak corresponds to rejuvenated short times, the other to overaged long times.
• Overaging arises because the entering rate Γ_in(E) increases due to overpopulation of low-energy states, while the escape rate Γ_out(E) remains unchanged.
• The SGR model predicts that complete rejuvenation is possible only if the elastic modulus depends on well depth (k = k₀ + κE), leading to a critical strain γ₀c = 2/κ.
• The model's prediction of logarithmic age dependence in instantaneous elastic modulus <k> ∝ log(t_w) matches experimental observations in pasty colloidal systems.