Aging after shear rejuvenation in a soft glassy colloidal suspension: Evidence for two different regimes

F. Ianni, R. Di Leonardo, S. Gentilini, and G. Ruocco

Phys. Rev. E 75, 011408 – Published 19 January 2007

Abstract

The aging dynamics after shear rejuvenation in a glassy clay suspension have been investigated through dynamic light scattering (DLS). Two different aging regimes are observed: one is attained if the sample is rejuvenated before its gelation and one after the rejuvenation of the gelled sample. In the first regime, the application of shear fully rejuvenates the sample, as the system dynamics soon after shear cessation follow the same aging evolution characteristic of standard aging. In the second regime, aging proceeds very fast after shear rejuvenation, and classical DLS cannot be used. An original protocol to measure an ensemble-averaged intensity-correlation function is proposed and its consistency with classical DLS is verified. The fast aging dynamics of rejuvenated gelled samples exhibit a power-law dependence of the slow relaxation time on the waiting time.

Received 19 July 2006

DOI:https://doi.org/10.1103/PhysRevE.75.011408

Authors & Affiliations

F. Ianni^1,2,*, R. Di Leonardo², S. Gentilini¹, and G. Ruocco^1,2

¹Dipartimento di Fisica, Universitá di Roma “La Sapienza,” I-00185 Roma, Italy
²SOFT-INFM-CNR, c/o Universitá di Roma “La Sapienza,” I-00185 Roma, Italy

^*Electronic address: francesca.ianni@phys.uniroma1.it

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 75, Iss. 1 — January 2007

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Intensity-correlation function measured as an ensemble average over many intensity acquisitions after shear cessation (thin line) compared to the time-averaged correlation function measured through classical DLS (bold line). Measurements are performed on a Laponite sample aging under shear at ${\dot{γ}}_{1} = 100 s^{- 1}$ for $24 h$ . As the sample ages during this long acquisition time, the correlation function plotted in a bold line is an average of all the correlation functions acquired during the experiment through classical DLS. Inset: For 14 waiting times values between 1 and $80 s$ , we plot the histograms of $Δ_{t_{w}} = n_{i} (t_{w}) n_{i} (t_{w} + \bar{t}) ∕ {\bar{n}}^{2}$ (with $\bar{t}$ satisfying the condition $g^{(2)} (t_{w}, \bar{t}) = e^{- 1}$ ) calculated for each acquisition $i$ among $N = 950$ acquisitions.Reuse & Permissions
Figure 2
Average slow relaxation time $⟨ τ_{s} ⟩$ is plotted as a function of waiting time $t_{w}$ for a sample aging soon after filtration (엯) and for the same sample aging after the application of a shear rate of $100 s^{- 1}$ for $2 \min$ , $13.4 h$ after filtration (●). $t_{w}$ is shifted in order to superimpose the first $⟨ τ_{s} ⟩$ measured after the application of shear with the standard aging curve. The black line is a guide for the eye. The fast aging regime, observed after shear rejuvenation of a gelled sample, is also plotted for comparison for the same applied shear rate $(+)$ . The curve is shifted in $t_{w}$ through the above-described procedure. Inset: fast relaxation time $τ_{f}$ as a function of $t_{w}$ for the two aging evolutions, plotted through the same procedure.Reuse & Permissions
Figure 3
Normalized intensity-autocorrelation functions for two different aging regimes after shear rejuvenation. Left: a Laponite sample rejuvenated before entering the arrested phase. Correlation functions are obtained through an average on the time origin for 16 equally spaced waiting times $t_{w}^{0}$ between 0.2 and $3 hours$ (from left to right) after shear cessation. Right: a gelled Laponite sample for a set of $t_{w}^{0}$ between 0.3 and $40 s$ (from left to right) after shear cessation. Correlation functions are obtained through the ensemble-average procedure. In this last case, the fast decay is not accessible.Reuse & Permissions
Figure 4
Difference of the two aging regimes after shear rejuvenation as evidenced from the evolution of the $β$ parameter, deduced from a stretched exponential fit $\exp [{(- t ∕ τ_{s})}^{β}]$ of the intensity-autocorrelation function. Left: aging of a sample rejuvenated before entering the arrested phase. Right: aging of a rejuvenated gelled sample.Reuse & Permissions
Figure 5
Fast slowing down of the scattered intensity fluctuations with the waiting time for a rejuvenated gelled Laponite sample. Top: the evolution of the counts revealed by the photomultiplier in $10^{- 2} s$ soon after shear cessation is plotted, $t_{w} = 0$ corresponds to the shear stop. Bottom: log-linear plot of the counts evolution; a logarithmic binning of $t_{w}$ has been performed and the counts have been averaged in each bin.Reuse & Permissions
Figure 6
Aging after rejuvenation of a gelled Laponite sample. The evolution with $t_{w}$ of the slow relaxation time $τ_{s}$ is plotted for various applied shear rates ${\dot{γ}}_{1}$ : (◇) $6 s^{- 1}$ , (◻) $28 s^{- 1}$ , (▴) $66 s^{- 1}$ , (엯) $134 s^{- 1}$ . The curves do not show significant variations for the different ${\dot{γ}}_{1}$ . The bold line is a fit to a $t_{w}^{- 1.2}$ power law.Reuse & Permissions

Physical Review E

covering statistical, nonlinear, biological, and soft matter physics